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mm, numa: rework do_pages_move 

Patch series "unclutter thp migration"

Motivation:

THP migration is hacked into the generic migration with rather
surprising semantic.  The migration allocation callback is supposed to
check whether the THP can be migrated at once and if that is not the
case then it allocates a simple page to migrate.  unmap_and_move then
fixes that up by splitting the THP into small pages while moving the
head page to the newly allocated order-0 page.  Remaining pages are
moved to the LRU list by split_huge_page.  The same happens if the THP
allocation fails.  This is really ugly and error prone [2].

I also believe that split_huge_page to the LRU lists is inherently wrong
because all tail pages are not migrated.  Some callers will just work
around that by retrying (e.g.  memory hotplug).  There are other pfn
walkers which are simply broken though.  e.g. madvise_inject_error will
migrate head and then advances next pfn by the huge page size.
do_move_page_to_node_array, queue_pages_range (migrate_pages, mbind),
will simply split the THP before migration if the THP migration is not
supported then falls back to single page migration but it doesn't handle
tail pages if the THP migration path is not able to allocate a fresh THP
so we end up with ENOMEM and fail the whole migration which is a
questionable behavior.  Page compaction doesn't try to migrate large
pages so it should be immune.

The first patch reworks do_pages_move which relies on a very ugly
calling semantic when the return status is pushed to the migration path
via private pointer.  It uses pre allocated fixed size batching to
achieve that.  We simply cannot do the same if a THP is to be split
during the migration path which is done in the patch 3.  Patch 2 is
follow up cleanup which removes the mentioned return status calling
convention ugliness.

On a side note:

There are some semantic issues I have encountered on the way when
working on patch 1 but I am not addressing them here.  E.g. trying to
move THP tail pages will result in either success or EBUSY (the later
one more likely once we isolate head from the LRU list).  Hugetlb
reports EACCESS on tail pages.  Some errors are reported via status
parameter but migration failures are not even though the original
`reason' argument suggests there was an intention to do so.  From a
quick look into git history this never worked.  I have tried to keep the
semantic unchanged.

Then there is a relatively minor thing that the page isolation might
fail because of pages not being on the LRU - e.g. because they are
sitting on the per-cpu LRU caches.  Easily fixable.

This patch (of 3):

do_pages_move is supposed to move user defined memory (an array of
addresses) to the user defined numa nodes (an array of nodes one for
each address).  The user provided status array then contains resulting
numa node for each address or an error.  The semantic of this function
is little bit confusing because only some errors are reported back.
Notably migrate_pages error is only reported via the return value.  This
patch doesn't try to address these semantic nuances but rather change
the underlying implementation.

Currently we are processing user input (which can be really large) in
batches which are stored to a temporarily allocated page.  Each address
is resolved to its struct page and stored to page_to_node structure
along with the requested target numa node.  The array of these
structures is then conveyed down the page migration path via private
argument.  new_page_node then finds the corresponding structure and
allocates the proper target page.

What is the problem with the current implementation and why to change
it? Apart from being quite ugly it also doesn't cope with unexpected
pages showing up on the migration list inside migrate_pages path.  That
doesn't happen currently but the follow up patch would like to make the
thp migration code more clear and that would need to split a THP into
the list for some cases.

How does the new implementation work? Well, instead of batching into a
fixed size array we simply batch all pages that should be migrated to
the same node and isolate all of them into a linked list which doesn't
require any additional storage.  This should work reasonably well
because page migration usually migrates larger ranges of memory to a
specific node.  So the common case should work equally well as the
current implementation.  Even if somebody constructs an input where the
target numa nodes would be interleaved we shouldn't see a large
performance impact because page migration alone doesn't really benefit
from batching.  mmap_sem batching for the lookup is quite questionable
and isolate_lru_page which would benefit from batching is not using it
even in the current implementation.

Link: http://lkml.kernel.org/r/20180103082555.14592-2-mhocko@kernel.org
Signed-off-by: Michal Hocko <mhocko@suse.com>
Acked-by: Kirill A. Shutemov <kirill@shutemov.name>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Cc: Zi Yan <zi.yan@cs.rutgers.edu>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrea Reale <ar@linux.vnet.ibm.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
hifive-unleashed-5.1
Michal Hocko 2018-04-10 16:29:59 -07:00 committed by Linus Torvalds
parent bfc6b1cabc
commit a49bd4d716
3 changed files with 142 additions and 178 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
mm/internal.h
View File

@ -538,4 +538,5 @@ static inline bool is_migrate_highatomic_page(struct page *page)
} }
void setup_zone_pageset(struct zone *zone); void setup_zone_pageset(struct zone *zone);
extern struct page *alloc_new_node_page(struct page *page, unsigned long node, int **x);
#endif /* __MM_INTERNAL_H */ #endif /* __MM_INTERNAL_H */

5
mm/mempolicy.c
View File

@ -942,7 +942,8 @@ static void migrate_page_add(struct page *page, struct list_head *pagelist,
} }
} }
static struct page *new_node_page(struct page *page, unsigned long node, int **x) /* page allocation callback for NUMA node migration */
struct page *alloc_new_node_page(struct page *page, unsigned long node, int **x)
{ {
if (PageHuge(page)) if (PageHuge(page))
return alloc_huge_page_node(page_hstate(compound_head(page)), return alloc_huge_page_node(page_hstate(compound_head(page)),
@ -986,7 +987,7 @@ static int migrate_to_node(struct mm_struct *mm, int source, int dest,
flags | MPOL_MF_DISCONTIG_OK, &pagelist); flags | MPOL_MF_DISCONTIG_OK, &pagelist);
if (!list_empty(&pagelist)) { if (!list_empty(&pagelist)) {
err = migrate_pages(&pagelist, new_node_page, NULL, dest, err = migrate_pages(&pagelist, alloc_new_node_page, NULL, dest,
MIGRATE_SYNC, MR_SYSCALL); MIGRATE_SYNC, MR_SYSCALL);
if (err) if (err)
putback_movable_pages(&pagelist); putback_movable_pages(&pagelist);

314
mm/migrate.c
View File

@ -1444,141 +1444,103 @@ out:
} }
#ifdef CONFIG_NUMA #ifdef CONFIG_NUMA
/*
* Move a list of individual pages
*/
struct page_to_node {
unsigned long addr;
struct page *page;
int node;
int status;
};
static struct page *new_page_node(struct page *p, unsigned long private, static int store_status(int __user *status, int start, int value, int nr)
int **result)
{ {
struct page_to_node *pm = (struct page_to_node *)private; while (nr-- > 0) {
if (put_user(value, status + start))
return -EFAULT;
start++;
}
while (pm->node != MAX_NUMNODES && pm->page != p) return 0;
pm++; }
if (pm->node == MAX_NUMNODES) static int do_move_pages_to_node(struct mm_struct *mm,
return NULL; struct list_head *pagelist, int node)
{
int err;
*result = &pm->status; if (list_empty(pagelist))
return 0;
if (PageHuge(p)) err = migrate_pages(pagelist, alloc_new_node_page, NULL, node,
return alloc_huge_page_node(page_hstate(compound_head(p)), MIGRATE_SYNC, MR_SYSCALL);
pm->node); if (err)
else if (thp_migration_supported() && PageTransHuge(p)) { putback_movable_pages(pagelist);
struct page *thp; return err;
thp = alloc_pages_node(pm->node,
(GFP_TRANSHUGE | __GFP_THISNODE) & ~__GFP_RECLAIM,
HPAGE_PMD_ORDER);
if (!thp)
return NULL;
prep_transhuge_page(thp);
return thp;
} else
return __alloc_pages_node(pm->node,
GFP_HIGHUSER_MOVABLE | __GFP_THISNODE, 0);
} }
/* /*
* Move a set of pages as indicated in the pm array. The addr * Resolves the given address to a struct page, isolates it from the LRU and
* field must be set to the virtual address of the page to be moved * puts it to the given pagelist.
* and the node number must contain a valid target node. * Returns -errno if the page cannot be found/isolated or 0 when it has been
* The pm array ends with node = MAX_NUMNODES. * queued or the page doesn't need to be migrated because it is already on
* the target node
*/ */
static int do_move_page_to_node_array(struct mm_struct *mm, static int add_page_for_migration(struct mm_struct *mm, unsigned long addr,
struct page_to_node *pm, int node, struct list_head *pagelist, bool migrate_all)
int migrate_all)
{ {
struct vm_area_struct *vma;
struct page *page;
unsigned int follflags;
int err; int err;
struct page_to_node *pp;
LIST_HEAD(pagelist);
down_read(&mm->mmap_sem); down_read(&mm->mmap_sem);
err = -EFAULT;
vma = find_vma(mm, addr);
if (!vma || addr < vma->vm_start || !vma_migratable(vma))
goto out;
/* /* FOLL_DUMP to ignore special (like zero) pages */
* Build a list of pages to migrate follflags = FOLL_GET | FOLL_DUMP;
*/ if (!thp_migration_supported())
for (pp = pm; pp->node != MAX_NUMNODES; pp++) { follflags |= FOLL_SPLIT;
struct vm_area_struct *vma; page = follow_page(vma, addr, follflags);
struct page *page;
struct page *head;
unsigned int follflags;
err = -EFAULT; err = PTR_ERR(page);
vma = find_vma(mm, pp->addr); if (IS_ERR(page))
if (!vma || pp->addr < vma->vm_start || !vma_migratable(vma)) goto out;
goto set_status;
/* FOLL_DUMP to ignore special (like zero) pages */ err = -ENOENT;
follflags = FOLL_GET | FOLL_DUMP; if (!page)
if (!thp_migration_supported()) goto out;
follflags |= FOLL_SPLIT;
page = follow_page(vma, pp->addr, follflags);
err = PTR_ERR(page);
if (IS_ERR(page))
goto set_status;
err = -ENOENT;
if (!page)
goto set_status;
err = page_to_nid(page);
if (err == pp->node)
/*
* Node already in the right place
*/
goto put_and_set;
err = -EACCES;
if (page_mapcount(page) > 1 &&
!migrate_all)
goto put_and_set;
if (PageHuge(page)) {
if (PageHead(page)) {
isolate_huge_page(page, &pagelist);
err = 0;
pp->page = page;
}
goto put_and_set;
}
pp->page = compound_head(page);
head = compound_head(page);
err = isolate_lru_page(head);
if (!err) {
list_add_tail(&head->lru, &pagelist);
mod_node_page_state(page_pgdat(head),
NR_ISOLATED_ANON + page_is_file_cache(head),
hpage_nr_pages(head));
}
put_and_set:
/*
* Either remove the duplicate refcount from
* isolate_lru_page() or drop the page ref if it was
* not isolated.
*/
put_page(page);
set_status:
pp->status = err;
}
err = 0; err = 0;
if (!list_empty(&pagelist)) { if (page_to_nid(page) == node)
err = migrate_pages(&pagelist, new_page_node, NULL, goto out_putpage;
(unsigned long)pm, MIGRATE_SYNC, MR_SYSCALL);
if (err)
putback_movable_pages(&pagelist);
}
err = -EACCES;
if (page_mapcount(page) > 1 && !migrate_all)
goto out_putpage;
if (PageHuge(page)) {
if (PageHead(page)) {
isolate_huge_page(page, pagelist);
err = 0;
}
} else {
struct page *head;
head = compound_head(page);
err = isolate_lru_page(head);
if (err)
goto out_putpage;
err = 0;
list_add_tail(&head->lru, pagelist);
mod_node_page_state(page_pgdat(head),
NR_ISOLATED_ANON + page_is_file_cache(head),
hpage_nr_pages(head));
}
out_putpage:
/*
* Either remove the duplicate refcount from
* isolate_lru_page() or drop the page ref if it was
* not isolated.
*/
put_page(page);
out:
up_read(&mm->mmap_sem); up_read(&mm->mmap_sem);
return err; return err;
} }
@ -1593,79 +1555,79 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
const int __user *nodes, const int __user *nodes,
int __user *status, int flags) int __user *status, int flags)
{ {
struct page_to_node *pm; int current_node = NUMA_NO_NODE;
unsigned long chunk_nr_pages; LIST_HEAD(pagelist);
unsigned long chunk_start; int start, i;
int err; int err = 0, err1;
err = -ENOMEM;
pm = (struct page_to_node *)__get_free_page(GFP_KERNEL);
if (!pm)
goto out;
migrate_prep(); migrate_prep();
/* for (i = start = 0; i < nr_pages; i++) {
* Store a chunk of page_to_node array in a page, const void __user *p;
* but keep the last one as a marker unsigned long addr;
*/ int node;
chunk_nr_pages = (PAGE_SIZE / sizeof(struct page_to_node)) - 1;
for (chunk_start = 0; err = -EFAULT;
chunk_start < nr_pages; if (get_user(p, pages + i))
chunk_start += chunk_nr_pages) { goto out_flush;
int j; if (get_user(node, nodes + i))
goto out_flush;
addr = (unsigned long)p;
if (chunk_start + chunk_nr_pages > nr_pages) err = -ENODEV;
chunk_nr_pages = nr_pages - chunk_start; if (node < 0 || node >= MAX_NUMNODES)
goto out_flush;
if (!node_state(node, N_MEMORY))
goto out_flush;
/* fill the chunk pm with addrs and nodes from user-space */ err = -EACCES;
for (j = 0; j < chunk_nr_pages; j++) { if (!node_isset(node, task_nodes))
const void __user *p; goto out_flush;
int node;
err = -EFAULT; if (current_node == NUMA_NO_NODE) {
if (get_user(p, pages + j + chunk_start)) current_node = node;
goto out_pm; start = i;
pm[j].addr = (unsigned long) p; } else if (node != current_node) {
err = do_move_pages_to_node(mm, &pagelist, current_node);
if (get_user(node, nodes + j + chunk_start)) if (err)
goto out_pm; goto out;
err = store_status(status, start, current_node, i - start);
err = -ENODEV; if (err)
if (node < 0 || node >= MAX_NUMNODES) goto out;
goto out_pm; start = i;
current_node = node;
if (!node_state(node, N_MEMORY))
goto out_pm;
err = -EACCES;
if (!node_isset(node, task_nodes))
goto out_pm;
pm[j].node = node;
} }
/* End marker for this chunk */ /*
pm[chunk_nr_pages].node = MAX_NUMNODES; * Errors in the page lookup or isolation are not fatal and we simply
* report them via status
*/
err = add_page_for_migration(mm, addr, current_node,
&pagelist, flags & MPOL_MF_MOVE_ALL);
if (!err)
continue;
/* Migrate this chunk */ err = store_status(status, i, err, 1);
err = do_move_page_to_node_array(mm, pm, if (err)
flags & MPOL_MF_MOVE_ALL); goto out_flush;
if (err < 0)
goto out_pm;
/* Return status information */ err = do_move_pages_to_node(mm, &pagelist, current_node);
for (j = 0; j < chunk_nr_pages; j++) if (err)
if (put_user(pm[j].status, status + j + chunk_start)) { goto out;
err = -EFAULT; if (i > start) {
goto out_pm; err = store_status(status, start, current_node, i - start);
} if (err)
goto out;
}
current_node = NUMA_NO_NODE;
} }
err = 0; out_flush:
/* Make sure we do not overwrite the existing error */
out_pm: err1 = do_move_pages_to_node(mm, &pagelist, current_node);
free_page((unsigned long)pm); if (!err1)
err1 = store_status(status, start, current_node, i - start);
if (!err)
err = err1;
out: out:
return err; return err;
} }