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remarkable-linux/mm/rmap.c
Andrea Arcangeli 71e3aac072 thp: transparent hugepage core 
Lately I've been working to make KVM use hugepages transparently without
the usual restrictions of hugetlbfs.  Some of the restrictions I'd like to
see removed:

1) hugepages have to be swappable or the guest physical memory remains
   locked in RAM and can't be paged out to swap

2) if a hugepage allocation fails, regular pages should be allocated
   instead and mixed in the same vma without any failure and without
   userland noticing

3) if some task quits and more hugepages become available in the
   buddy, guest physical memory backed by regular pages should be
   relocated on hugepages automatically in regions under
   madvise(MADV_HUGEPAGE) (ideally event driven by waking up the
   kernel deamon if the order=HPAGE_PMD_SHIFT-PAGE_SHIFT list becomes
   not null)

4) avoidance of reservation and maximization of use of hugepages whenever
   possible. Reservation (needed to avoid runtime fatal faliures) may be ok for
   1 machine with 1 database with 1 database cache with 1 database cache size
   known at boot time. It's definitely not feasible with a virtualization
   hypervisor usage like RHEV-H that runs an unknown number of virtual machines
   with an unknown size of each virtual machine with an unknown amount of
   pagecache that could be potentially useful in the host for guest not using
   O_DIRECT (aka cache=off).

hugepages in the virtualization hypervisor (and also in the guest!) are
much more important than in a regular host not using virtualization,
becasue with NPT/EPT they decrease the tlb-miss cacheline accesses from 24
to 19 in case only the hypervisor uses transparent hugepages, and they
decrease the tlb-miss cacheline accesses from 19 to 15 in case both the
linux hypervisor and the linux guest both uses this patch (though the
guest will limit the addition speedup to anonymous regions only for
now...).  Even more important is that the tlb miss handler is much slower
on a NPT/EPT guest than for a regular shadow paging or no-virtualization
scenario.  So maximizing the amount of virtual memory cached by the TLB
pays off significantly more with NPT/EPT than without (even if there would
be no significant speedup in the tlb-miss runtime).

The first (and more tedious) part of this work requires allowing the VM to
handle anonymous hugepages mixed with regular pages transparently on
regular anonymous vmas.  This is what this patch tries to achieve in the
least intrusive possible way.  We want hugepages and hugetlb to be used in
a way so that all applications can benefit without changes (as usual we
leverage the KVM virtualization design: by improving the Linux VM at
large, KVM gets the performance boost too).

The most important design choice is: always fallback to 4k allocation if
the hugepage allocation fails!  This is the _very_ opposite of some large
pagecache patches that failed with -EIO back then if a 64k (or similar)
allocation failed...

Second important decision (to reduce the impact of the feature on the
existing pagetable handling code) is that at any time we can split an
hugepage into 512 regular pages and it has to be done with an operation
that can't fail.  This way the reliability of the swapping isn't decreased
(no need to allocate memory when we are short on memory to swap) and it's
trivial to plug a split_huge_page* one-liner where needed without
polluting the VM.  Over time we can teach mprotect, mremap and friends to
handle pmd_trans_huge natively without calling split_huge_page*.  The fact
it can't fail isn't just for swap: if split_huge_page would return -ENOMEM
(instead of the current void) we'd need to rollback the mprotect from the
middle of it (ideally including undoing the split_vma) which would be a
big change and in the very wrong direction (it'd likely be simpler not to
call split_huge_page at all and to teach mprotect and friends to handle
hugepages instead of rolling them back from the middle).  In short the
very value of split_huge_page is that it can't fail.

The collapsing and madvise(MADV_HUGEPAGE) part will remain separated and
incremental and it'll just be an "harmless" addition later if this initial
part is agreed upon.  It also should be noted that locking-wise replacing
regular pages with hugepages is going to be very easy if compared to what
I'm doing below in split_huge_page, as it will only happen when
page_count(page) matches page_mapcount(page) if we can take the PG_lock
and mmap_sem in write mode.  collapse_huge_page will be a "best effort"
that (unlike split_huge_page) can fail at the minimal sign of trouble and
we can try again later.  collapse_huge_page will be similar to how KSM
works and the madvise(MADV_HUGEPAGE) will work similar to
madvise(MADV_MERGEABLE).

The default I like is that transparent hugepages are used at page fault
time.  This can be changed with
/sys/kernel/mm/transparent_hugepage/enabled.  The control knob can be set
to three values "always", "madvise", "never" which mean respectively that
hugepages are always used, or only inside madvise(MADV_HUGEPAGE) regions,
or never used.  /sys/kernel/mm/transparent_hugepage/defrag instead
controls if the hugepage allocation should defrag memory aggressively
"always", only inside "madvise" regions, or "never".

The pmd_trans_splitting/pmd_trans_huge locking is very solid.  The
put_page (from get_user_page users that can't use mmu notifier like
O_DIRECT) that runs against a __split_huge_page_refcount instead was a
pain to serialize in a way that would result always in a coherent page
count for both tail and head.  I think my locking solution with a
compound_lock taken only after the page_first is valid and is still a
PageHead should be safe but it surely needs review from SMP race point of
view.  In short there is no current existing way to serialize the O_DIRECT
final put_page against split_huge_page_refcount so I had to invent a new
one (O_DIRECT loses knowledge on the mapping status by the time gup_fast
returns so...).  And I didn't want to impact all gup/gup_fast users for
now, maybe if we change the gup interface substantially we can avoid this
locking, I admit I didn't think too much about it because changing the gup
unpinning interface would be invasive.

If we ignored O_DIRECT we could stick to the existing compound refcounting
code, by simply adding a get_user_pages_fast_flags(foll_flags) where KVM
(and any other mmu notifier user) would call it without FOLL_GET (and if
FOLL_GET isn't set we'd just BUG_ON if nobody registered itself in the
current task mmu notifier list yet).  But O_DIRECT is fundamental for
decent performance of virtualized I/O on fast storage so we can't avoid it
to solve the race of put_page against split_huge_page_refcount to achieve
a complete hugepage feature for KVM.

Swap and oom works fine (well just like with regular pages ;).  MMU
notifier is handled transparently too, with the exception of the young bit
on the pmd, that didn't have a range check but I think KVM will be fine
because the whole point of hugepages is that EPT/NPT will also use a huge
pmd when they notice gup returns pages with PageCompound set, so they
won't care of a range and there's just the pmd young bit to check in that
case.

NOTE: in some cases if the L2 cache is small, this may slowdown and waste
memory during COWs because 4M of memory are accessed in a single fault
instead of 8k (the payoff is that after COW the program can run faster).
So we might want to switch the copy_huge_page (and clear_huge_page too) to
not temporal stores.  I also extensively researched ways to avoid this
cache trashing with a full prefault logic that would cow in 8k/16k/32k/64k
up to 1M (I can send those patches that fully implemented prefault) but I
concluded they're not worth it and they add an huge additional complexity
and they remove all tlb benefits until the full hugepage has been faulted
in, to save a little bit of memory and some cache during app startup, but
they still don't improve substantially the cache-trashing during startup
if the prefault happens in >4k chunks.  One reason is that those 4k pte
entries copied are still mapped on a perfectly cache-colored hugepage, so
the trashing is the worst one can generate in those copies (cow of 4k page
copies aren't so well colored so they trashes less, but again this results
in software running faster after the page fault).  Those prefault patches
allowed things like a pte where post-cow pages were local 4k regular anon
pages and the not-yet-cowed pte entries were pointing in the middle of
some hugepage mapped read-only.  If it doesn't payoff substantially with
todays hardware it will payoff even less in the future with larger l2
caches, and the prefault logic would blot the VM a lot.  If one is
emebdded transparent_hugepage can be disabled during boot with sysfs or
with the boot commandline parameter transparent_hugepage=0 (or
transparent_hugepage=2 to restrict hugepages inside madvise regions) that
will ensure not a single hugepage is allocated at boot time.  It is simple
enough to just disable transparent hugepage globally and let transparent
hugepages be allocated selectively by applications in the MADV_HUGEPAGE
region (both at page fault time, and if enabled with the
collapse_huge_page too through the kernel daemon).

This patch supports only hugepages mapped in the pmd, archs that have
smaller hugepages will not fit in this patch alone.  Also some archs like
power have certain tlb limits that prevents mixing different page size in
the same regions so they will not fit in this framework that requires
"graceful fallback" to basic PAGE_SIZE in case of physical memory
fragmentation.  hugetlbfs remains a perfect fit for those because its
software limits happen to match the hardware limits.  hugetlbfs also
remains a perfect fit for hugepage sizes like 1GByte that cannot be hoped
to be found not fragmented after a certain system uptime and that would be
very expensive to defragment with relocation, so requiring reservation.
hugetlbfs is the "reservation way", the point of transparent hugepages is
not to have any reservation at all and maximizing the use of cache and
hugepages at all times automatically.

Some performance result:

vmx andrea # LD_PRELOAD=/usr/lib64/libhugetlbfs.so HUGETLB_MORECORE=yes HUGETLB_PATH=/mnt/huge/ ./largep
ages3
memset page fault 1566023
memset tlb miss 453854
memset second tlb miss 453321
random access tlb miss 41635
random access second tlb miss 41658
vmx andrea # LD_PRELOAD=/usr/lib64/libhugetlbfs.so HUGETLB_MORECORE=yes HUGETLB_PATH=/mnt/huge/ ./largepages3
memset page fault 1566471
memset tlb miss 453375
memset second tlb miss 453320
random access tlb miss 41636
random access second tlb miss 41637
vmx andrea # ./largepages3
memset page fault 1566642
memset tlb miss 453417
memset second tlb miss 453313
random access tlb miss 41630
random access second tlb miss 41647
vmx andrea # ./largepages3
memset page fault 1566872
memset tlb miss 453418
memset second tlb miss 453315
random access tlb miss 41618
random access second tlb miss 41659
vmx andrea # echo 0 > /proc/sys/vm/transparent_hugepage
vmx andrea # ./largepages3
memset page fault 2182476
memset tlb miss 460305
memset second tlb miss 460179
random access tlb miss 44483
random access second tlb miss 44186
vmx andrea # ./largepages3
memset page fault 2182791
memset tlb miss 460742
memset second tlb miss 459962
random access tlb miss 43981
random access second tlb miss 43988

============
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/time.h>

#define SIZE (3UL*1024*1024*1024)

int main()
{
	char *p = malloc(SIZE), *p2;
	struct timeval before, after;

	gettimeofday(&before, NULL);
	memset(p, 0, SIZE);
	gettimeofday(&after, NULL);
	printf("memset page fault %Lu\n",
	       (after.tv_sec-before.tv_sec)*1000000UL +
	       after.tv_usec-before.tv_usec);

	gettimeofday(&before, NULL);
	memset(p, 0, SIZE);
	gettimeofday(&after, NULL);
	printf("memset tlb miss %Lu\n",
	       (after.tv_sec-before.tv_sec)*1000000UL +
	       after.tv_usec-before.tv_usec);

	gettimeofday(&before, NULL);
	memset(p, 0, SIZE);
	gettimeofday(&after, NULL);
	printf("memset second tlb miss %Lu\n",
	       (after.tv_sec-before.tv_sec)*1000000UL +
	       after.tv_usec-before.tv_usec);

	gettimeofday(&before, NULL);
	for (p2 = p; p2 < p+SIZE; p2 += 4096)
		*p2 = 0;
	gettimeofday(&after, NULL);
	printf("random access tlb miss %Lu\n",
	       (after.tv_sec-before.tv_sec)*1000000UL +
	       after.tv_usec-before.tv_usec);

	gettimeofday(&before, NULL);
	for (p2 = p; p2 < p+SIZE; p2 += 4096)
		*p2 = 0;
	gettimeofday(&after, NULL);
	printf("random access second tlb miss %Lu\n",
	       (after.tv_sec-before.tv_sec)*1000000UL +
	       after.tv_usec-before.tv_usec);

	return 0;
}
============

Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Acked-by: Rik van Riel <riel@redhat.com>
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-01-13 17:32:42 -08:00

1616 lines
46 KiB
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/*
* mm/rmap.c - physical to virtual reverse mappings
*
* Copyright 2001, Rik van Riel <riel@conectiva.com.br>
* Released under the General Public License (GPL).
*
* Simple, low overhead reverse mapping scheme.
* Please try to keep this thing as modular as possible.
*
* Provides methods for unmapping each kind of mapped page:
* the anon methods track anonymous pages, and
* the file methods track pages belonging to an inode.
*
* Original design by Rik van Riel <riel@conectiva.com.br> 2001
* File methods by Dave McCracken <dmccr@us.ibm.com> 2003, 2004
* Anonymous methods by Andrea Arcangeli <andrea@suse.de> 2004
* Contributions by Hugh Dickins 2003, 2004
*/
/*
* Lock ordering in mm:
*
* inode->i_mutex (while writing or truncating, not reading or faulting)
* inode->i_alloc_sem (vmtruncate_range)
* mm->mmap_sem
* page->flags PG_locked (lock_page)
* mapping->i_mmap_lock
* anon_vma->lock
* mm->page_table_lock or pte_lock
* zone->lru_lock (in mark_page_accessed, isolate_lru_page)
* swap_lock (in swap_duplicate, swap_info_get)
* mmlist_lock (in mmput, drain_mmlist and others)
* mapping->private_lock (in __set_page_dirty_buffers)
* inode_lock (in set_page_dirty's __mark_inode_dirty)
* sb_lock (within inode_lock in fs/fs-writeback.c)
* mapping->tree_lock (widely used, in set_page_dirty,
* in arch-dependent flush_dcache_mmap_lock,
* within inode_lock in __sync_single_inode)
*
* (code doesn't rely on that order so it could be switched around)
* ->tasklist_lock
* anon_vma->lock (memory_failure, collect_procs_anon)
* pte map lock
*/
#include <linux/mm.h>
#include <linux/pagemap.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/ksm.h>
#include <linux/rmap.h>
#include <linux/rcupdate.h>
#include <linux/module.h>
#include <linux/memcontrol.h>
#include <linux/mmu_notifier.h>
#include <linux/migrate.h>
#include <linux/hugetlb.h>
#include <asm/tlbflush.h>
#include "internal.h"
static struct kmem_cache *anon_vma_cachep;
static struct kmem_cache *anon_vma_chain_cachep;
static inline struct anon_vma *anon_vma_alloc(void)
{
return kmem_cache_alloc(anon_vma_cachep, GFP_KERNEL);
}
void anon_vma_free(struct anon_vma *anon_vma)
{
kmem_cache_free(anon_vma_cachep, anon_vma);
}
static inline struct anon_vma_chain *anon_vma_chain_alloc(void)
{
return kmem_cache_alloc(anon_vma_chain_cachep, GFP_KERNEL);
}
static void anon_vma_chain_free(struct anon_vma_chain *anon_vma_chain)
{
kmem_cache_free(anon_vma_chain_cachep, anon_vma_chain);
}
/**
* anon_vma_prepare - attach an anon_vma to a memory region
* @vma: the memory region in question
*
* This makes sure the memory mapping described by 'vma' has
* an 'anon_vma' attached to it, so that we can associate the
* anonymous pages mapped into it with that anon_vma.
*
* The common case will be that we already have one, but if
* not we either need to find an adjacent mapping that we
* can re-use the anon_vma from (very common when the only
* reason for splitting a vma has been mprotect()), or we
* allocate a new one.
*
* Anon-vma allocations are very subtle, because we may have
* optimistically looked up an anon_vma in page_lock_anon_vma()
* and that may actually touch the spinlock even in the newly
* allocated vma (it depends on RCU to make sure that the
* anon_vma isn't actually destroyed).
*
* As a result, we need to do proper anon_vma locking even
* for the new allocation. At the same time, we do not want
* to do any locking for the common case of already having
* an anon_vma.
*
* This must be called with the mmap_sem held for reading.
*/
int anon_vma_prepare(struct vm_area_struct *vma)
{
struct anon_vma *anon_vma = vma->anon_vma;
struct anon_vma_chain *avc;
might_sleep();
if (unlikely(!anon_vma)) {
struct mm_struct *mm = vma->vm_mm;
struct anon_vma *allocated;
avc = anon_vma_chain_alloc();
if (!avc)
goto out_enomem;
anon_vma = find_mergeable_anon_vma(vma);
allocated = NULL;
if (!anon_vma) {
anon_vma = anon_vma_alloc();
if (unlikely(!anon_vma))
goto out_enomem_free_avc;
allocated = anon_vma;
/*
* This VMA had no anon_vma yet. This anon_vma is
* the root of any anon_vma tree that might form.
*/
anon_vma->root = anon_vma;
}
anon_vma_lock(anon_vma);
/* page_table_lock to protect against threads */
spin_lock(&mm->page_table_lock);
if (likely(!vma->anon_vma)) {
vma->anon_vma = anon_vma;
avc->anon_vma = anon_vma;
avc->vma = vma;
list_add(&avc->same_vma, &vma->anon_vma_chain);
list_add_tail(&avc->same_anon_vma, &anon_vma->head);
allocated = NULL;
avc = NULL;
}
spin_unlock(&mm->page_table_lock);
anon_vma_unlock(anon_vma);
if (unlikely(allocated))
anon_vma_free(allocated);
if (unlikely(avc))
anon_vma_chain_free(avc);
}
return 0;
out_enomem_free_avc:
anon_vma_chain_free(avc);
out_enomem:
return -ENOMEM;
}
static void anon_vma_chain_link(struct vm_area_struct *vma,
struct anon_vma_chain *avc,
struct anon_vma *anon_vma)
{
avc->vma = vma;
avc->anon_vma = anon_vma;
list_add(&avc->same_vma, &vma->anon_vma_chain);
anon_vma_lock(anon_vma);
list_add_tail(&avc->same_anon_vma, &anon_vma->head);
anon_vma_unlock(anon_vma);
}
/*
* Attach the anon_vmas from src to dst.
* Returns 0 on success, -ENOMEM on failure.
*/
int anon_vma_clone(struct vm_area_struct *dst, struct vm_area_struct *src)
{
struct anon_vma_chain *avc, *pavc;
list_for_each_entry_reverse(pavc, &src->anon_vma_chain, same_vma) {
avc = anon_vma_chain_alloc();
if (!avc)
goto enomem_failure;
anon_vma_chain_link(dst, avc, pavc->anon_vma);
}
return 0;
enomem_failure:
unlink_anon_vmas(dst);
return -ENOMEM;
}
/*
* Attach vma to its own anon_vma, as well as to the anon_vmas that
* the corresponding VMA in the parent process is attached to.
* Returns 0 on success, non-zero on failure.
*/
int anon_vma_fork(struct vm_area_struct *vma, struct vm_area_struct *pvma)
{
struct anon_vma_chain *avc;
struct anon_vma *anon_vma;
/* Don't bother if the parent process has no anon_vma here. */
if (!pvma->anon_vma)
return 0;
/*
* First, attach the new VMA to the parent VMA's anon_vmas,
* so rmap can find non-COWed pages in child processes.
*/
if (anon_vma_clone(vma, pvma))
return -ENOMEM;
/* Then add our own anon_vma. */
anon_vma = anon_vma_alloc();
if (!anon_vma)
goto out_error;
avc = anon_vma_chain_alloc();
if (!avc)
goto out_error_free_anon_vma;
/*
* The root anon_vma's spinlock is the lock actually used when we
* lock any of the anon_vmas in this anon_vma tree.
*/
anon_vma->root = pvma->anon_vma->root;
/*
* With KSM refcounts, an anon_vma can stay around longer than the
* process it belongs to. The root anon_vma needs to be pinned
* until this anon_vma is freed, because the lock lives in the root.
*/
get_anon_vma(anon_vma->root);
/* Mark this anon_vma as the one where our new (COWed) pages go. */
vma->anon_vma = anon_vma;
anon_vma_chain_link(vma, avc, anon_vma);
return 0;
out_error_free_anon_vma:
anon_vma_free(anon_vma);
out_error:
unlink_anon_vmas(vma);
return -ENOMEM;
}
static void anon_vma_unlink(struct anon_vma_chain *anon_vma_chain)
{
struct anon_vma *anon_vma = anon_vma_chain->anon_vma;
int empty;
/* If anon_vma_fork fails, we can get an empty anon_vma_chain. */
if (!anon_vma)
return;
anon_vma_lock(anon_vma);
list_del(&anon_vma_chain->same_anon_vma);
/* We must garbage collect the anon_vma if it's empty */
empty = list_empty(&anon_vma->head) && !anonvma_external_refcount(anon_vma);
anon_vma_unlock(anon_vma);
if (empty) {
/* We no longer need the root anon_vma */
if (anon_vma->root != anon_vma)
drop_anon_vma(anon_vma->root);
anon_vma_free(anon_vma);
}
}
void unlink_anon_vmas(struct vm_area_struct *vma)
{
struct anon_vma_chain *avc, *next;
/*
* Unlink each anon_vma chained to the VMA. This list is ordered
* from newest to oldest, ensuring the root anon_vma gets freed last.
*/
list_for_each_entry_safe(avc, next, &vma->anon_vma_chain, same_vma) {
anon_vma_unlink(avc);
list_del(&avc->same_vma);
anon_vma_chain_free(avc);
}
}
static void anon_vma_ctor(void *data)
{
struct anon_vma *anon_vma = data;
spin_lock_init(&anon_vma->lock);
anonvma_external_refcount_init(anon_vma);
INIT_LIST_HEAD(&anon_vma->head);
}
void __init anon_vma_init(void)
{
anon_vma_cachep = kmem_cache_create("anon_vma", sizeof(struct anon_vma),
0, SLAB_DESTROY_BY_RCU|SLAB_PANIC, anon_vma_ctor);
anon_vma_chain_cachep = KMEM_CACHE(anon_vma_chain, SLAB_PANIC);
}
/*
* Getting a lock on a stable anon_vma from a page off the LRU is
* tricky: page_lock_anon_vma rely on RCU to guard against the races.
*/
struct anon_vma *__page_lock_anon_vma(struct page *page)
{
struct anon_vma *anon_vma, *root_anon_vma;
unsigned long anon_mapping;
rcu_read_lock();
anon_mapping = (unsigned long) ACCESS_ONCE(page->mapping);
if ((anon_mapping & PAGE_MAPPING_FLAGS) != PAGE_MAPPING_ANON)
goto out;
if (!page_mapped(page))
goto out;
anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON);
root_anon_vma = ACCESS_ONCE(anon_vma->root);
spin_lock(&root_anon_vma->lock);
/*
* If this page is still mapped, then its anon_vma cannot have been
* freed. But if it has been unmapped, we have no security against
* the anon_vma structure being freed and reused (for another anon_vma:
* SLAB_DESTROY_BY_RCU guarantees that - so the spin_lock above cannot
* corrupt): with anon_vma_prepare() or anon_vma_fork() redirecting
* anon_vma->root before page_unlock_anon_vma() is called to unlock.
*/
if (page_mapped(page))
return anon_vma;
spin_unlock(&root_anon_vma->lock);
out:
rcu_read_unlock();
return NULL;
}
void page_unlock_anon_vma(struct anon_vma *anon_vma)
__releases(&anon_vma->root->lock)
__releases(RCU)
{
anon_vma_unlock(anon_vma);
rcu_read_unlock();
}
/*
* At what user virtual address is page expected in @vma?
* Returns virtual address or -EFAULT if page's index/offset is not
* within the range mapped the @vma.
*/
inline unsigned long
vma_address(struct page *page, struct vm_area_struct *vma)
{
pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
unsigned long address;
if (unlikely(is_vm_hugetlb_page(vma)))
pgoff = page->index << huge_page_order(page_hstate(page));
address = vma->vm_start + ((pgoff - vma->vm_pgoff) << PAGE_SHIFT);
if (unlikely(address < vma->vm_start || address >= vma->vm_end)) {
/* page should be within @vma mapping range */
return -EFAULT;
}
return address;
}
/*
* At what user virtual address is page expected in vma?
* Caller should check the page is actually part of the vma.
*/
unsigned long page_address_in_vma(struct page *page, struct vm_area_struct *vma)
{
if (PageAnon(page)) {
struct anon_vma *page__anon_vma = page_anon_vma(page);
/*
* Note: swapoff's unuse_vma() is more efficient with this
* check, and needs it to match anon_vma when KSM is active.
*/
if (!vma->anon_vma || !page__anon_vma ||
vma->anon_vma->root != page__anon_vma->root)
return -EFAULT;
} else if (page->mapping && !(vma->vm_flags & VM_NONLINEAR)) {
if (!vma->vm_file ||
vma->vm_file->f_mapping != page->mapping)
return -EFAULT;
} else
return -EFAULT;
return vma_address(page, vma);
}
/*
* Check that @page is mapped at @address into @mm.
*
* If @sync is false, page_check_address may perform a racy check to avoid
* the page table lock when the pte is not present (helpful when reclaiming
* highly shared pages).
*
* On success returns with pte mapped and locked.
*/
pte_t *__page_check_address(struct page *page, struct mm_struct *mm,
unsigned long address, spinlock_t **ptlp, int sync)
{
pgd_t *pgd;
pud_t *pud;
pmd_t *pmd;
pte_t *pte;
spinlock_t *ptl;
if (unlikely(PageHuge(page))) {
pte = huge_pte_offset(mm, address);
ptl = &mm->page_table_lock;
goto check;
}
pgd = pgd_offset(mm, address);
if (!pgd_present(*pgd))
return NULL;
pud = pud_offset(pgd, address);
if (!pud_present(*pud))
return NULL;
pmd = pmd_offset(pud, address);
if (!pmd_present(*pmd))
return NULL;
if (pmd_trans_huge(*pmd))
return NULL;
pte = pte_offset_map(pmd, address);
/* Make a quick check before getting the lock */
if (!sync && !pte_present(*pte)) {
pte_unmap(pte);
return NULL;
}
ptl = pte_lockptr(mm, pmd);
check:
spin_lock(ptl);
if (pte_present(*pte) && page_to_pfn(page) == pte_pfn(*pte)) {
*ptlp = ptl;
return pte;
}
pte_unmap_unlock(pte, ptl);
return NULL;
}
/**
* page_mapped_in_vma - check whether a page is really mapped in a VMA
* @page: the page to test
* @vma: the VMA to test
*
* Returns 1 if the page is mapped into the page tables of the VMA, 0
* if the page is not mapped into the page tables of this VMA. Only
* valid for normal file or anonymous VMAs.
*/
int page_mapped_in_vma(struct page *page, struct vm_area_struct *vma)
{
unsigned long address;
pte_t *pte;
spinlock_t *ptl;
address = vma_address(page, vma);
if (address == -EFAULT) /* out of vma range */
return 0;
pte = page_check_address(page, vma->vm_mm, address, &ptl, 1);
if (!pte) /* the page is not in this mm */
return 0;
pte_unmap_unlock(pte, ptl);
return 1;
}
/*
* Subfunctions of page_referenced: page_referenced_one called
* repeatedly from either page_referenced_anon or page_referenced_file.
*/
int page_referenced_one(struct page *page, struct vm_area_struct *vma,
unsigned long address, unsigned int *mapcount,
unsigned long *vm_flags)
{
struct mm_struct *mm = vma->vm_mm;
int referenced = 0;
/*
* Don't want to elevate referenced for mlocked page that gets this far,
* in order that it progresses to try_to_unmap and is moved to the
* unevictable list.
*/
if (vma->vm_flags & VM_LOCKED) {
*mapcount = 0; /* break early from loop */
*vm_flags |= VM_LOCKED;
goto out;
}
/* Pretend the page is referenced if the task has the
swap token and is in the middle of a page fault. */
if (mm != current->mm && has_swap_token(mm) &&
rwsem_is_locked(&mm->mmap_sem))
referenced++;
if (unlikely(PageTransHuge(page))) {
pmd_t *pmd;
spin_lock(&mm->page_table_lock);
pmd = page_check_address_pmd(page, mm, address,
PAGE_CHECK_ADDRESS_PMD_FLAG);
if (pmd && !pmd_trans_splitting(*pmd) &&
pmdp_clear_flush_young_notify(vma, address, pmd))
referenced++;
spin_unlock(&mm->page_table_lock);
} else {
pte_t *pte;
spinlock_t *ptl;
pte = page_check_address(page, mm, address, &ptl, 0);
if (!pte)
goto out;
if (ptep_clear_flush_young_notify(vma, address, pte)) {
/*
* Don't treat a reference through a sequentially read
* mapping as such. If the page has been used in
* another mapping, we will catch it; if this other
* mapping is already gone, the unmap path will have
* set PG_referenced or activated the page.
*/
if (likely(!VM_SequentialReadHint(vma)))
referenced++;
}
pte_unmap_unlock(pte, ptl);
}
(*mapcount)--;
if (referenced)
*vm_flags |= vma->vm_flags;
out:
return referenced;
}
static int page_referenced_anon(struct page *page,
struct mem_cgroup *mem_cont,
unsigned long *vm_flags)
{
unsigned int mapcount;
struct anon_vma *anon_vma;
struct anon_vma_chain *avc;
int referenced = 0;
anon_vma = page_lock_anon_vma(page);
if (!anon_vma)
return referenced;
mapcount = page_mapcount(page);
list_for_each_entry(avc, &anon_vma->head, same_anon_vma) {
struct vm_area_struct *vma = avc->vma;
unsigned long address = vma_address(page, vma);
if (address == -EFAULT)
continue;
/*
* If we are reclaiming on behalf of a cgroup, skip
* counting on behalf of references from different
* cgroups
*/
if (mem_cont && !mm_match_cgroup(vma->vm_mm, mem_cont))
continue;
referenced += page_referenced_one(page, vma, address,
&mapcount, vm_flags);
if (!mapcount)
break;
}
page_unlock_anon_vma(anon_vma);
return referenced;
}
/**
* page_referenced_file - referenced check for object-based rmap
* @page: the page we're checking references on.
* @mem_cont: target memory controller
* @vm_flags: collect encountered vma->vm_flags who actually referenced the page
*
* For an object-based mapped page, find all the places it is mapped and
* check/clear the referenced flag. This is done by following the page->mapping
* pointer, then walking the chain of vmas it holds. It returns the number
* of references it found.
*
* This function is only called from page_referenced for object-based pages.
*/
static int page_referenced_file(struct page *page,
struct mem_cgroup *mem_cont,
unsigned long *vm_flags)
{
unsigned int mapcount;
struct address_space *mapping = page->mapping;
pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
struct vm_area_struct *vma;
struct prio_tree_iter iter;
int referenced = 0;
/*
* The caller's checks on page->mapping and !PageAnon have made
* sure that this is a file page: the check for page->mapping
* excludes the case just before it gets set on an anon page.
*/
BUG_ON(PageAnon(page));
/*
* The page lock not only makes sure that page->mapping cannot
* suddenly be NULLified by truncation, it makes sure that the
* structure at mapping cannot be freed and reused yet,
* so we can safely take mapping->i_mmap_lock.
*/
BUG_ON(!PageLocked(page));
spin_lock(&mapping->i_mmap_lock);
/*
* i_mmap_lock does not stabilize mapcount at all, but mapcount
* is more likely to be accurate if we note it after spinning.
*/
mapcount = page_mapcount(page);
vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
unsigned long address = vma_address(page, vma);
if (address == -EFAULT)
continue;
/*
* If we are reclaiming on behalf of a cgroup, skip
* counting on behalf of references from different
* cgroups
*/
if (mem_cont && !mm_match_cgroup(vma->vm_mm, mem_cont))
continue;
referenced += page_referenced_one(page, vma, address,
&mapcount, vm_flags);
if (!mapcount)
break;
}
spin_unlock(&mapping->i_mmap_lock);
return referenced;
}
/**
* page_referenced - test if the page was referenced
* @page: the page to test
* @is_locked: caller holds lock on the page
* @mem_cont: target memory controller
* @vm_flags: collect encountered vma->vm_flags who actually referenced the page
*
* Quick test_and_clear_referenced for all mappings to a page,
* returns the number of ptes which referenced the page.
*/
int page_referenced(struct page *page,
int is_locked,
struct mem_cgroup *mem_cont,
unsigned long *vm_flags)
{
int referenced = 0;
int we_locked = 0;
*vm_flags = 0;
if (page_mapped(page) && page_rmapping(page)) {
if (!is_locked && (!PageAnon(page) || PageKsm(page))) {
we_locked = trylock_page(page);
if (!we_locked) {
referenced++;
goto out;
}
}
if (unlikely(PageKsm(page)))
referenced += page_referenced_ksm(page, mem_cont,
vm_flags);
else if (PageAnon(page))
referenced += page_referenced_anon(page, mem_cont,
vm_flags);
else if (page->mapping)
referenced += page_referenced_file(page, mem_cont,
vm_flags);
if (we_locked)
unlock_page(page);
}
out:
if (page_test_and_clear_young(page))
referenced++;
return referenced;
}
static int page_mkclean_one(struct page *page, struct vm_area_struct *vma,
unsigned long address)
{
struct mm_struct *mm = vma->vm_mm;
pte_t *pte;
spinlock_t *ptl;
int ret = 0;
pte = page_check_address(page, mm, address, &ptl, 1);
if (!pte)
goto out;
if (pte_dirty(*pte) || pte_write(*pte)) {
pte_t entry;
flush_cache_page(vma, address, pte_pfn(*pte));
entry = ptep_clear_flush_notify(vma, address, pte);
entry = pte_wrprotect(entry);
entry = pte_mkclean(entry);
set_pte_at(mm, address, pte, entry);
ret = 1;
}
pte_unmap_unlock(pte, ptl);
out:
return ret;
}
static int page_mkclean_file(struct address_space *mapping, struct page *page)
{
pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
struct vm_area_struct *vma;
struct prio_tree_iter iter;
int ret = 0;
BUG_ON(PageAnon(page));
spin_lock(&mapping->i_mmap_lock);
vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
if (vma->vm_flags & VM_SHARED) {
unsigned long address = vma_address(page, vma);
if (address == -EFAULT)
continue;
ret += page_mkclean_one(page, vma, address);
}
}
spin_unlock(&mapping->i_mmap_lock);
return ret;
}
int page_mkclean(struct page *page)
{
int ret = 0;
BUG_ON(!PageLocked(page));
if (page_mapped(page)) {
struct address_space *mapping = page_mapping(page);
if (mapping) {
ret = page_mkclean_file(mapping, page);
if (page_test_dirty(page)) {
page_clear_dirty(page, 1);
ret = 1;
}
}
}
return ret;
}
EXPORT_SYMBOL_GPL(page_mkclean);
/**
* page_move_anon_rmap - move a page to our anon_vma
* @page: the page to move to our anon_vma
* @vma: the vma the page belongs to
* @address: the user virtual address mapped
*
* When a page belongs exclusively to one process after a COW event,
* that page can be moved into the anon_vma that belongs to just that
* process, so the rmap code will not search the parent or sibling
* processes.
*/
void page_move_anon_rmap(struct page *page,
struct vm_area_struct *vma, unsigned long address)
{
struct anon_vma *anon_vma = vma->anon_vma;
VM_BUG_ON(!PageLocked(page));
VM_BUG_ON(!anon_vma);
VM_BUG_ON(page->index != linear_page_index(vma, address));
anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
page->mapping = (struct address_space *) anon_vma;
}
/**
* __page_set_anon_rmap - set up new anonymous rmap
* @page: Page to add to rmap
* @vma: VM area to add page to.
* @address: User virtual address of the mapping
* @exclusive: the page is exclusively owned by the current process
*/
static void __page_set_anon_rmap(struct page *page,
struct vm_area_struct *vma, unsigned long address, int exclusive)
{
struct anon_vma *anon_vma = vma->anon_vma;
BUG_ON(!anon_vma);
if (PageAnon(page))
return;
/*
* If the page isn't exclusively mapped into this vma,
* we must use the _oldest_ possible anon_vma for the
* page mapping!
*/
if (!exclusive)
anon_vma = anon_vma->root;
anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
page->mapping = (struct address_space *) anon_vma;
page->index = linear_page_index(vma, address);
}
/**
* __page_check_anon_rmap - sanity check anonymous rmap addition
* @page: the page to add the mapping to
* @vma: the vm area in which the mapping is added
* @address: the user virtual address mapped
*/
static void __page_check_anon_rmap(struct page *page,
struct vm_area_struct *vma, unsigned long address)
{
#ifdef CONFIG_DEBUG_VM
/*
* The page's anon-rmap details (mapping and index) are guaranteed to
* be set up correctly at this point.
*
* We have exclusion against page_add_anon_rmap because the caller
* always holds the page locked, except if called from page_dup_rmap,
* in which case the page is already known to be setup.
*
* We have exclusion against page_add_new_anon_rmap because those pages
* are initially only visible via the pagetables, and the pte is locked
* over the call to page_add_new_anon_rmap.
*/
BUG_ON(page_anon_vma(page)->root != vma->anon_vma->root);
BUG_ON(page->index != linear_page_index(vma, address));
#endif
}
/**
* page_add_anon_rmap - add pte mapping to an anonymous page
* @page: the page to add the mapping to
* @vma: the vm area in which the mapping is added
* @address: the user virtual address mapped
*
* The caller needs to hold the pte lock, and the page must be locked in
* the anon_vma case: to serialize mapping,index checking after setting,
* and to ensure that PageAnon is not being upgraded racily to PageKsm
* (but PageKsm is never downgraded to PageAnon).
*/
void page_add_anon_rmap(struct page *page,
struct vm_area_struct *vma, unsigned long address)
{
do_page_add_anon_rmap(page, vma, address, 0);
}
/*
* Special version of the above for do_swap_page, which often runs
* into pages that are exclusively owned by the current process.
* Everybody else should continue to use page_add_anon_rmap above.
*/
void do_page_add_anon_rmap(struct page *page,
struct vm_area_struct *vma, unsigned long address, int exclusive)
{
int first = atomic_inc_and_test(&page->_mapcount);
if (first)
__inc_zone_page_state(page, NR_ANON_PAGES);
if (unlikely(PageKsm(page)))
return;
VM_BUG_ON(!PageLocked(page));
VM_BUG_ON(address < vma->vm_start || address >= vma->vm_end);
if (first)
__page_set_anon_rmap(page, vma, address, exclusive);
else
__page_check_anon_rmap(page, vma, address);
}
/**
* page_add_new_anon_rmap - add pte mapping to a new anonymous page
* @page: the page to add the mapping to
* @vma: the vm area in which the mapping is added
* @address: the user virtual address mapped
*
* Same as page_add_anon_rmap but must only be called on *new* pages.
* This means the inc-and-test can be bypassed.
* Page does not have to be locked.
*/
void page_add_new_anon_rmap(struct page *page,
struct vm_area_struct *vma, unsigned long address)
{
VM_BUG_ON(address < vma->vm_start || address >= vma->vm_end);
SetPageSwapBacked(page);
atomic_set(&page->_mapcount, 0); /* increment count (starts at -1) */
__inc_zone_page_state(page, NR_ANON_PAGES);
__page_set_anon_rmap(page, vma, address, 1);
if (page_evictable(page, vma))
lru_cache_add_lru(page, LRU_ACTIVE_ANON);
else
add_page_to_unevictable_list(page);
}
/**
* page_add_file_rmap - add pte mapping to a file page
* @page: the page to add the mapping to
*
* The caller needs to hold the pte lock.
*/
void page_add_file_rmap(struct page *page)
{
if (atomic_inc_and_test(&page->_mapcount)) {
__inc_zone_page_state(page, NR_FILE_MAPPED);
mem_cgroup_update_file_mapped(page, 1);
}
}
/**
* page_remove_rmap - take down pte mapping from a page
* @page: page to remove mapping from
*
* The caller needs to hold the pte lock.
*/
void page_remove_rmap(struct page *page)
{
/* page still mapped by someone else? */
if (!atomic_add_negative(-1, &page->_mapcount))
return;
/*
* Now that the last pte has gone, s390 must transfer dirty
* flag from storage key to struct page. We can usually skip
* this if the page is anon, so about to be freed; but perhaps
* not if it's in swapcache - there might be another pte slot
* containing the swap entry, but page not yet written to swap.
*/
if ((!PageAnon(page) || PageSwapCache(page)) && page_test_dirty(page)) {
page_clear_dirty(page, 1);
set_page_dirty(page);
}
/*
* Hugepages are not counted in NR_ANON_PAGES nor NR_FILE_MAPPED
* and not charged by memcg for now.
*/
if (unlikely(PageHuge(page)))
return;
if (PageAnon(page)) {
mem_cgroup_uncharge_page(page);
__dec_zone_page_state(page, NR_ANON_PAGES);
} else {
__dec_zone_page_state(page, NR_FILE_MAPPED);
mem_cgroup_update_file_mapped(page, -1);
}
/*
* It would be tidy to reset the PageAnon mapping here,
* but that might overwrite a racing page_add_anon_rmap
* which increments mapcount after us but sets mapping
* before us: so leave the reset to free_hot_cold_page,
* and remember that it's only reliable while mapped.
* Leaving it set also helps swapoff to reinstate ptes
* faster for those pages still in swapcache.
*/
}
/*
* Subfunctions of try_to_unmap: try_to_unmap_one called
* repeatedly from either try_to_unmap_anon or try_to_unmap_file.
*/
int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
unsigned long address, enum ttu_flags flags)
{
struct mm_struct *mm = vma->vm_mm;
pte_t *pte;
pte_t pteval;
spinlock_t *ptl;
int ret = SWAP_AGAIN;
pte = page_check_address(page, mm, address, &ptl, 0);
if (!pte)
goto out;
/*
* If the page is mlock()d, we cannot swap it out.
* If it's recently referenced (perhaps page_referenced
* skipped over this mm) then we should reactivate it.
*/
if (!(flags & TTU_IGNORE_MLOCK)) {
if (vma->vm_flags & VM_LOCKED)
goto out_mlock;
if (TTU_ACTION(flags) == TTU_MUNLOCK)
goto out_unmap;
}
if (!(flags & TTU_IGNORE_ACCESS)) {
if (ptep_clear_flush_young_notify(vma, address, pte)) {
ret = SWAP_FAIL;
goto out_unmap;
}
}
/* Nuke the page table entry. */
flush_cache_page(vma, address, page_to_pfn(page));
pteval = ptep_clear_flush_notify(vma, address, pte);
/* Move the dirty bit to the physical page now the pte is gone. */
if (pte_dirty(pteval))
set_page_dirty(page);
/* Update high watermark before we lower rss */
update_hiwater_rss(mm);
if (PageHWPoison(page) && !(flags & TTU_IGNORE_HWPOISON)) {
if (PageAnon(page))
dec_mm_counter(mm, MM_ANONPAGES);
else
dec_mm_counter(mm, MM_FILEPAGES);
set_pte_at(mm, address, pte,
swp_entry_to_pte(make_hwpoison_entry(page)));
} else if (PageAnon(page)) {
swp_entry_t entry = { .val = page_private(page) };
if (PageSwapCache(page)) {
/*
* Store the swap location in the pte.
* See handle_pte_fault() ...
*/
if (swap_duplicate(entry) < 0) {
set_pte_at(mm, address, pte, pteval);
ret = SWAP_FAIL;
goto out_unmap;
}
if (list_empty(&mm->mmlist)) {
spin_lock(&mmlist_lock);
if (list_empty(&mm->mmlist))
list_add(&mm->mmlist, &init_mm.mmlist);
spin_unlock(&mmlist_lock);
}
dec_mm_counter(mm, MM_ANONPAGES);
inc_mm_counter(mm, MM_SWAPENTS);
} else if (PAGE_MIGRATION) {
/*
* Store the pfn of the page in a special migration
* pte. do_swap_page() will wait until the migration
* pte is removed and then restart fault handling.
*/
BUG_ON(TTU_ACTION(flags) != TTU_MIGRATION);
entry = make_migration_entry(page, pte_write(pteval));
}
set_pte_at(mm, address, pte, swp_entry_to_pte(entry));
BUG_ON(pte_file(*pte));
} else if (PAGE_MIGRATION && (TTU_ACTION(flags) == TTU_MIGRATION)) {
/* Establish migration entry for a file page */
swp_entry_t entry;
entry = make_migration_entry(page, pte_write(pteval));
set_pte_at(mm, address, pte, swp_entry_to_pte(entry));
} else
dec_mm_counter(mm, MM_FILEPAGES);
page_remove_rmap(page);
page_cache_release(page);
out_unmap:
pte_unmap_unlock(pte, ptl);
out:
return ret;
out_mlock:
pte_unmap_unlock(pte, ptl);
/*
* We need mmap_sem locking, Otherwise VM_LOCKED check makes
* unstable result and race. Plus, We can't wait here because
* we now hold anon_vma->lock or mapping->i_mmap_lock.
* if trylock failed, the page remain in evictable lru and later
* vmscan could retry to move the page to unevictable lru if the
* page is actually mlocked.
*/
if (down_read_trylock(&vma->vm_mm->mmap_sem)) {
if (vma->vm_flags & VM_LOCKED) {
mlock_vma_page(page);
ret = SWAP_MLOCK;
}
up_read(&vma->vm_mm->mmap_sem);
}
return ret;
}
/*
* objrmap doesn't work for nonlinear VMAs because the assumption that
* offset-into-file correlates with offset-into-virtual-addresses does not hold.
* Consequently, given a particular page and its ->index, we cannot locate the
* ptes which are mapping that page without an exhaustive linear search.
*
* So what this code does is a mini "virtual scan" of each nonlinear VMA which
* maps the file to which the target page belongs. The ->vm_private_data field
* holds the current cursor into that scan. Successive searches will circulate
* around the vma's virtual address space.
*
* So as more replacement pressure is applied to the pages in a nonlinear VMA,
* more scanning pressure is placed against them as well. Eventually pages
* will become fully unmapped and are eligible for eviction.
*
* For very sparsely populated VMAs this is a little inefficient - chances are
* there there won't be many ptes located within the scan cluster. In this case
* maybe we could scan further - to the end of the pte page, perhaps.
*
* Mlocked pages: check VM_LOCKED under mmap_sem held for read, if we can
* acquire it without blocking. If vma locked, mlock the pages in the cluster,
* rather than unmapping them. If we encounter the "check_page" that vmscan is
* trying to unmap, return SWAP_MLOCK, else default SWAP_AGAIN.
*/
#define CLUSTER_SIZE min(32*PAGE_SIZE, PMD_SIZE)
#define CLUSTER_MASK (~(CLUSTER_SIZE - 1))
static int try_to_unmap_cluster(unsigned long cursor, unsigned int *mapcount,
struct vm_area_struct *vma, struct page *check_page)
{
struct mm_struct *mm = vma->vm_mm;
pgd_t *pgd;
pud_t *pud;
pmd_t *pmd;
pte_t *pte;
pte_t pteval;
spinlock_t *ptl;
struct page *page;
unsigned long address;
unsigned long end;
int ret = SWAP_AGAIN;
int locked_vma = 0;
address = (vma->vm_start + cursor) & CLUSTER_MASK;
end = address + CLUSTER_SIZE;
if (address < vma->vm_start)
address = vma->vm_start;
if (end > vma->vm_end)
end = vma->vm_end;
pgd = pgd_offset(mm, address);
if (!pgd_present(*pgd))
return ret;
pud = pud_offset(pgd, address);
if (!pud_present(*pud))
return ret;
pmd = pmd_offset(pud, address);
if (!pmd_present(*pmd))
return ret;
/*
* If we can acquire the mmap_sem for read, and vma is VM_LOCKED,
* keep the sem while scanning the cluster for mlocking pages.
*/
if (down_read_trylock(&vma->vm_mm->mmap_sem)) {
locked_vma = (vma->vm_flags & VM_LOCKED);
if (!locked_vma)
up_read(&vma->vm_mm->mmap_sem); /* don't need it */
}
pte = pte_offset_map_lock(mm, pmd, address, &ptl);
/* Update high watermark before we lower rss */
update_hiwater_rss(mm);
for (; address < end; pte++, address += PAGE_SIZE) {
if (!pte_present(*pte))
continue;
page = vm_normal_page(vma, address, *pte);
BUG_ON(!page || PageAnon(page));
if (locked_vma) {
mlock_vma_page(page); /* no-op if already mlocked */
if (page == check_page)
ret = SWAP_MLOCK;
continue; /* don't unmap */
}
if (ptep_clear_flush_young_notify(vma, address, pte))
continue;
/* Nuke the page table entry. */
flush_cache_page(vma, address, pte_pfn(*pte));
pteval = ptep_clear_flush_notify(vma, address, pte);
/* If nonlinear, store the file page offset in the pte. */
if (page->index != linear_page_index(vma, address))
set_pte_at(mm, address, pte, pgoff_to_pte(page->index));
/* Move the dirty bit to the physical page now the pte is gone. */
if (pte_dirty(pteval))
set_page_dirty(page);
page_remove_rmap(page);
page_cache_release(page);
dec_mm_counter(mm, MM_FILEPAGES);
(*mapcount)--;
}
pte_unmap_unlock(pte - 1, ptl);
if (locked_vma)
up_read(&vma->vm_mm->mmap_sem);
return ret;
}
bool is_vma_temporary_stack(struct vm_area_struct *vma)
{
int maybe_stack = vma->vm_flags & (VM_GROWSDOWN | VM_GROWSUP);
if (!maybe_stack)
return false;
if ((vma->vm_flags & VM_STACK_INCOMPLETE_SETUP) ==
VM_STACK_INCOMPLETE_SETUP)
return true;
return false;
}
/**
* try_to_unmap_anon - unmap or unlock anonymous page using the object-based
* rmap method
* @page: the page to unmap/unlock
* @flags: action and flags
*
* Find all the mappings of a page using the mapping pointer and the vma chains
* contained in the anon_vma struct it points to.
*
* This function is only called from try_to_unmap/try_to_munlock for
* anonymous pages.
* When called from try_to_munlock(), the mmap_sem of the mm containing the vma
* where the page was found will be held for write. So, we won't recheck
* vm_flags for that VMA. That should be OK, because that vma shouldn't be
* 'LOCKED.
*/
static int try_to_unmap_anon(struct page *page, enum ttu_flags flags)
{
struct anon_vma *anon_vma;
struct anon_vma_chain *avc;
int ret = SWAP_AGAIN;
anon_vma = page_lock_anon_vma(page);
if (!anon_vma)
return ret;
list_for_each_entry(avc, &anon_vma->head, same_anon_vma) {
struct vm_area_struct *vma = avc->vma;
unsigned long address;
/*
* During exec, a temporary VMA is setup and later moved.
* The VMA is moved under the anon_vma lock but not the
* page tables leading to a race where migration cannot
* find the migration ptes. Rather than increasing the
* locking requirements of exec(), migration skips
* temporary VMAs until after exec() completes.
*/
if (PAGE_MIGRATION && (flags & TTU_MIGRATION) &&
is_vma_temporary_stack(vma))
continue;
address = vma_address(page, vma);
if (address == -EFAULT)
continue;
ret = try_to_unmap_one(page, vma, address, flags);
if (ret != SWAP_AGAIN || !page_mapped(page))
break;
}
page_unlock_anon_vma(anon_vma);
return ret;
}
/**
* try_to_unmap_file - unmap/unlock file page using the object-based rmap method
* @page: the page to unmap/unlock
* @flags: action and flags
*
* Find all the mappings of a page using the mapping pointer and the vma chains
* contained in the address_space struct it points to.
*
* This function is only called from try_to_unmap/try_to_munlock for
* object-based pages.
* When called from try_to_munlock(), the mmap_sem of the mm containing the vma
* where the page was found will be held for write. So, we won't recheck
* vm_flags for that VMA. That should be OK, because that vma shouldn't be
* 'LOCKED.
*/
static int try_to_unmap_file(struct page *page, enum ttu_flags flags)
{
struct address_space *mapping = page->mapping;
pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
struct vm_area_struct *vma;
struct prio_tree_iter iter;
int ret = SWAP_AGAIN;
unsigned long cursor;
unsigned long max_nl_cursor = 0;
unsigned long max_nl_size = 0;
unsigned int mapcount;
spin_lock(&mapping->i_mmap_lock);
vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
unsigned long address = vma_address(page, vma);
if (address == -EFAULT)
continue;
ret = try_to_unmap_one(page, vma, address, flags);
if (ret != SWAP_AGAIN || !page_mapped(page))
goto out;
}
if (list_empty(&mapping->i_mmap_nonlinear))
goto out;
/*
* We don't bother to try to find the munlocked page in nonlinears.
* It's costly. Instead, later, page reclaim logic may call
* try_to_unmap(TTU_MUNLOCK) and recover PG_mlocked lazily.
*/
if (TTU_ACTION(flags) == TTU_MUNLOCK)
goto out;
list_for_each_entry(vma, &mapping->i_mmap_nonlinear,
shared.vm_set.list) {
cursor = (unsigned long) vma->vm_private_data;
if (cursor > max_nl_cursor)
max_nl_cursor = cursor;
cursor = vma->vm_end - vma->vm_start;
if (cursor > max_nl_size)
max_nl_size = cursor;
}
if (max_nl_size == 0) { /* all nonlinears locked or reserved ? */
ret = SWAP_FAIL;
goto out;
}
/*
* We don't try to search for this page in the nonlinear vmas,
* and page_referenced wouldn't have found it anyway. Instead
* just walk the nonlinear vmas trying to age and unmap some.
* The mapcount of the page we came in with is irrelevant,
* but even so use it as a guide to how hard we should try?
*/
mapcount = page_mapcount(page);
if (!mapcount)
goto out;
cond_resched_lock(&mapping->i_mmap_lock);
max_nl_size = (max_nl_size + CLUSTER_SIZE - 1) & CLUSTER_MASK;
if (max_nl_cursor == 0)
max_nl_cursor = CLUSTER_SIZE;
do {
list_for_each_entry(vma, &mapping->i_mmap_nonlinear,
shared.vm_set.list) {
cursor = (unsigned long) vma->vm_private_data;
while ( cursor < max_nl_cursor &&
cursor < vma->vm_end - vma->vm_start) {
if (try_to_unmap_cluster(cursor, &mapcount,
vma, page) == SWAP_MLOCK)
ret = SWAP_MLOCK;
cursor += CLUSTER_SIZE;
vma->vm_private_data = (void *) cursor;
if ((int)mapcount <= 0)
goto out;
}
vma->vm_private_data = (void *) max_nl_cursor;
}
cond_resched_lock(&mapping->i_mmap_lock);
max_nl_cursor += CLUSTER_SIZE;
} while (max_nl_cursor <= max_nl_size);
/*
* Don't loop forever (perhaps all the remaining pages are
* in locked vmas). Reset cursor on all unreserved nonlinear
* vmas, now forgetting on which ones it had fallen behind.
*/
list_for_each_entry(vma, &mapping->i_mmap_nonlinear, shared.vm_set.list)
vma->vm_private_data = NULL;
out:
spin_unlock(&mapping->i_mmap_lock);
return ret;
}
/**
* try_to_unmap - try to remove all page table mappings to a page
* @page: the page to get unmapped
* @flags: action and flags
*
* Tries to remove all the page table entries which are mapping this
* page, used in the pageout path. Caller must hold the page lock.
* Return values are:
*
* SWAP_SUCCESS - we succeeded in removing all mappings
* SWAP_AGAIN - we missed a mapping, try again later
* SWAP_FAIL - the page is unswappable
* SWAP_MLOCK - page is mlocked.
*/
int try_to_unmap(struct page *page, enum ttu_flags flags)
{
int ret;
BUG_ON(!PageLocked(page));
BUG_ON(PageTransHuge(page));
if (unlikely(PageKsm(page)))
ret = try_to_unmap_ksm(page, flags);
else if (PageAnon(page))
ret = try_to_unmap_anon(page, flags);
else
ret = try_to_unmap_file(page, flags);
if (ret != SWAP_MLOCK && !page_mapped(page))
ret = SWAP_SUCCESS;
return ret;
}
/**
* try_to_munlock - try to munlock a page
* @page: the page to be munlocked
*
* Called from munlock code. Checks all of the VMAs mapping the page
* to make sure nobody else has this page mlocked. The page will be
* returned with PG_mlocked cleared if no other vmas have it mlocked.
*
* Return values are:
*
* SWAP_AGAIN - no vma is holding page mlocked, or,
* SWAP_AGAIN - page mapped in mlocked vma -- couldn't acquire mmap sem
* SWAP_FAIL - page cannot be located at present
* SWAP_MLOCK - page is now mlocked.
*/
int try_to_munlock(struct page *page)
{
VM_BUG_ON(!PageLocked(page) || PageLRU(page));
if (unlikely(PageKsm(page)))
return try_to_unmap_ksm(page, TTU_MUNLOCK);
else if (PageAnon(page))
return try_to_unmap_anon(page, TTU_MUNLOCK);
else
return try_to_unmap_file(page, TTU_MUNLOCK);
}
#if defined(CONFIG_KSM) || defined(CONFIG_MIGRATION)
/*
* Drop an anon_vma refcount, freeing the anon_vma and anon_vma->root
* if necessary. Be careful to do all the tests under the lock. Once
* we know we are the last user, nobody else can get a reference and we
* can do the freeing without the lock.
*/
void drop_anon_vma(struct anon_vma *anon_vma)
{
BUG_ON(atomic_read(&anon_vma->external_refcount) <= 0);
if (atomic_dec_and_lock(&anon_vma->external_refcount, &anon_vma->root->lock)) {
struct anon_vma *root = anon_vma->root;
int empty = list_empty(&anon_vma->head);
int last_root_user = 0;
int root_empty = 0;
/*
* The refcount on a non-root anon_vma got dropped. Drop
* the refcount on the root and check if we need to free it.
*/
if (empty && anon_vma != root) {
BUG_ON(atomic_read(&root->external_refcount) <= 0);
last_root_user = atomic_dec_and_test(&root->external_refcount);
root_empty = list_empty(&root->head);
}
anon_vma_unlock(anon_vma);
if (empty) {
anon_vma_free(anon_vma);
if (root_empty && last_root_user)
anon_vma_free(root);
}
}
}
#endif
#ifdef CONFIG_MIGRATION
/*
* rmap_walk() and its helpers rmap_walk_anon() and rmap_walk_file():
* Called by migrate.c to remove migration ptes, but might be used more later.
*/
static int rmap_walk_anon(struct page *page, int (*rmap_one)(struct page *,
struct vm_area_struct *, unsigned long, void *), void *arg)
{
struct anon_vma *anon_vma;
struct anon_vma_chain *avc;
int ret = SWAP_AGAIN;
/*
* Note: remove_migration_ptes() cannot use page_lock_anon_vma()
* because that depends on page_mapped(); but not all its usages
* are holding mmap_sem. Users without mmap_sem are required to
* take a reference count to prevent the anon_vma disappearing
*/
anon_vma = page_anon_vma(page);
if (!anon_vma)
return ret;
anon_vma_lock(anon_vma);
list_for_each_entry(avc, &anon_vma->head, same_anon_vma) {
struct vm_area_struct *vma = avc->vma;
unsigned long address = vma_address(page, vma);
if (address == -EFAULT)
continue;
ret = rmap_one(page, vma, address, arg);
if (ret != SWAP_AGAIN)
break;
}
anon_vma_unlock(anon_vma);
return ret;
}
static int rmap_walk_file(struct page *page, int (*rmap_one)(struct page *,
struct vm_area_struct *, unsigned long, void *), void *arg)
{
struct address_space *mapping = page->mapping;
pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
struct vm_area_struct *vma;
struct prio_tree_iter iter;
int ret = SWAP_AGAIN;
if (!mapping)
return ret;
spin_lock(&mapping->i_mmap_lock);
vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
unsigned long address = vma_address(page, vma);
if (address == -EFAULT)
continue;
ret = rmap_one(page, vma, address, arg);
if (ret != SWAP_AGAIN)
break;
}
/*
* No nonlinear handling: being always shared, nonlinear vmas
* never contain migration ptes. Decide what to do about this
* limitation to linear when we need rmap_walk() on nonlinear.
*/
spin_unlock(&mapping->i_mmap_lock);
return ret;
}
int rmap_walk(struct page *page, int (*rmap_one)(struct page *,
struct vm_area_struct *, unsigned long, void *), void *arg)
{
VM_BUG_ON(!PageLocked(page));
if (unlikely(PageKsm(page)))
return rmap_walk_ksm(page, rmap_one, arg);
else if (PageAnon(page))
return rmap_walk_anon(page, rmap_one, arg);
else
return rmap_walk_file(page, rmap_one, arg);
}
#endif /* CONFIG_MIGRATION */
#ifdef CONFIG_HUGETLB_PAGE
/*
* The following three functions are for anonymous (private mapped) hugepages.
* Unlike common anonymous pages, anonymous hugepages have no accounting code
* and no lru code, because we handle hugepages differently from common pages.
*/
static void __hugepage_set_anon_rmap(struct page *page,
struct vm_area_struct *vma, unsigned long address, int exclusive)
{
struct anon_vma *anon_vma = vma->anon_vma;
BUG_ON(!anon_vma);
if (PageAnon(page))
return;
if (!exclusive)
anon_vma = anon_vma->root;
anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
page->mapping = (struct address_space *) anon_vma;
page->index = linear_page_index(vma, address);
}
void hugepage_add_anon_rmap(struct page *page,
struct vm_area_struct *vma, unsigned long address)
{
struct anon_vma *anon_vma = vma->anon_vma;
int first;
BUG_ON(!PageLocked(page));
BUG_ON(!anon_vma);
BUG_ON(address < vma->vm_start || address >= vma->vm_end);
first = atomic_inc_and_test(&page->_mapcount);
if (first)
__hugepage_set_anon_rmap(page, vma, address, 0);
}
void hugepage_add_new_anon_rmap(struct page *page,
struct vm_area_struct *vma, unsigned long address)
{
BUG_ON(address < vma->vm_start || address >= vma->vm_end);
atomic_set(&page->_mapcount, 0);
__hugepage_set_anon_rmap(page, vma, address, 1);
}
#endif /* CONFIG_HUGETLB_PAGE */
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