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radix-tree: improve multiorder iterators 

This fixes several interlinked problems with the iterators in the
presence of multiorder entries.

1. radix_tree_iter_next() would only advance by one slot, which would
   result in the iterators returning the same entry more than once if
   there were sibling entries.

2. radix_tree_next_slot() could return an internal pointer instead of
   a user pointer if a tagged multiorder entry was immediately followed by
   an entry of lower order.

3. radix_tree_next_slot() expanded to a lot more code than it used to
   when multiorder support was compiled in.  And I wasn't comfortable with
   entry_to_node() being in a header file.

Fixing radix_tree_iter_next() for the presence of sibling entries
necessarily involves examining the contents of the radix tree, so we now
need to pass 'slot' to radix_tree_iter_next(), and we need to change the
calling convention so it is called *before* dropping the lock which
protects the tree.  Also rename it to radix_tree_iter_resume(), as some
people thought it was necessary to call radix_tree_iter_next() each time
around the loop.

radix_tree_next_slot() becomes closer to how it looked before multiorder
support was introduced.  It only checks to see if the next entry in the
chunk is a sibling entry or a pointer to a node; this should be rare
enough that handling this case out of line is not a performance impact
(and such impact is amortised by the fact that the entry we just
processed was a multiorder entry).  Also, radix_tree_next_slot() used to
force a new chunk lookup for untagged entries, which is more expensive
than the out of line sibling entry skipping.

Link: http://lkml.kernel.org/r/1480369871-5271-55-git-send-email-mawilcox@linuxonhyperv.com
Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
Tested-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Matthew Wilcox <mawilcox@microsoft.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
zero-colors
Matthew Wilcox 2016-12-14 15:08:49 -08:00 committed by Linus Torvalds
parent b35df27a39
commit 148deab223
9 changed files with 188 additions and 85 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
fs/btrfs/tests/btrfs-tests.c
View File

@ -162,7 +162,7 @@ void btrfs_free_dummy_fs_info(struct btrfs_fs_info *fs_info)
slot = radix_tree_iter_retry(&iter);
continue;
}
slot = radix_tree_iter_next(&iter);
slot = radix_tree_iter_resume(slot, &iter);
spin_unlock(&fs_info->buffer_lock);
free_extent_buffer_stale(eb);
spin_lock(&fs_info->buffer_lock);

71
include/linux/radix-tree.h
View File

@ -403,20 +403,17 @@ __radix_tree_iter_add(struct radix_tree_iter *iter, unsigned long slots)
}
/**
* radix_tree_iter_next - resume iterating when the chunk may be invalid
* @iter: iterator state
* radix_tree_iter_resume - resume iterating when the chunk may be invalid
* @slot: pointer to current slot
* @iter: iterator state
* Returns: New slot pointer
*
* If the iterator needs to release then reacquire a lock, the chunk may
* have been invalidated by an insertion or deletion. Call this function
* to continue the iteration from the next index.
* before releasing the lock to continue the iteration from the next index.
*/
static inline __must_check
void **radix_tree_iter_next(struct radix_tree_iter *iter)
{
iter->next_index = __radix_tree_iter_add(iter, 1);
iter->tags = 0;
return NULL;
}
void **__must_check radix_tree_iter_resume(void **slot,
struct radix_tree_iter *iter);
/**
* radix_tree_chunk_size - get current chunk size
@ -430,10 +427,17 @@ radix_tree_chunk_size(struct radix_tree_iter *iter)
return (iter->next_index - iter->index) >> iter_shift(iter);
}
static inline struct radix_tree_node *entry_to_node(void *ptr)
#ifdef CONFIG_RADIX_TREE_MULTIORDER
void ** __radix_tree_next_slot(void **slot, struct radix_tree_iter *iter,
unsigned flags);
#else
/* Can't happen without sibling entries, but the compiler can't tell that */
static inline void ** __radix_tree_next_slot(void **slot,
struct radix_tree_iter *iter, unsigned flags)
{
return (void *)((unsigned long)ptr & ~RADIX_TREE_INTERNAL_NODE);
return slot;
}
#endif
/**
* radix_tree_next_slot - find next slot in chunk
@ -447,7 +451,7 @@ static inline struct radix_tree_node *entry_to_node(void *ptr)
* For tagged lookup it also eats @iter->tags.
*
* There are several cases where 'slot' can be passed in as NULL to this
* function. These cases result from the use of radix_tree_iter_next() or
* function. These cases result from the use of radix_tree_iter_resume() or
* radix_tree_iter_retry(). In these cases we don't end up dereferencing
* 'slot' because either:
* a) we are doing tagged iteration and iter->tags has been set to 0, or
@ -458,51 +462,31 @@ static __always_inline void **
radix_tree_next_slot(void **slot, struct radix_tree_iter *iter, unsigned flags)
{
if (flags & RADIX_TREE_ITER_TAGGED) {
void *canon = slot;
iter->tags >>= 1;
if (unlikely(!iter->tags))
return NULL;
while (IS_ENABLED(CONFIG_RADIX_TREE_MULTIORDER) &&
radix_tree_is_internal_node(slot[1])) {
if (entry_to_node(slot[1]) == canon) {
iter->tags >>= 1;
iter->index = __radix_tree_iter_add(iter, 1);
slot++;
continue;
}
iter->next_index = __radix_tree_iter_add(iter, 1);
return NULL;
}
if (likely(iter->tags & 1ul)) {
iter->index = __radix_tree_iter_add(iter, 1);
return slot + 1;
slot++;
goto found;
}
if (!(flags & RADIX_TREE_ITER_CONTIG)) {
unsigned offset = __ffs(iter->tags);
iter->tags >>= offset;
iter->index = __radix_tree_iter_add(iter, offset + 1);
return slot + offset + 1;
iter->tags >>= offset++;
iter->index = __radix_tree_iter_add(iter, offset);
slot += offset;
goto found;
}
} else {
long count = radix_tree_chunk_size(iter);
void *canon = slot;
while (--count > 0) {
slot++;
iter->index = __radix_tree_iter_add(iter, 1);
if (IS_ENABLED(CONFIG_RADIX_TREE_MULTIORDER) &&
radix_tree_is_internal_node(*slot)) {
if (entry_to_node(*slot) == canon)
continue;
iter->next_index = iter->index;
break;
}
if (likely(*slot))
return slot;
goto found;
if (flags & RADIX_TREE_ITER_CONTIG) {
/* forbid switching to the next chunk */
iter->next_index = 0;
@ -511,6 +495,11 @@ radix_tree_next_slot(void **slot, struct radix_tree_iter *iter, unsigned flags)
}
}
return NULL;
found:
if (unlikely(radix_tree_is_internal_node(*slot)))
return __radix_tree_next_slot(slot, iter, flags);
return slot;
}
/**
@ -561,6 +550,6 @@ radix_tree_next_slot(void **slot, struct radix_tree_iter *iter, unsigned flags)
slot || (slot = radix_tree_next_chunk(root, iter, \
RADIX_TREE_ITER_TAGGED | tag)) ; \
slot = radix_tree_next_slot(slot, iter, \
RADIX_TREE_ITER_TAGGED))
RADIX_TREE_ITER_TAGGED | tag))
#endif /* _LINUX_RADIX_TREE_H */

138
lib/radix-tree.c
View File

@ -69,6 +69,11 @@ struct radix_tree_preload {
};
static DEFINE_PER_CPU(struct radix_tree_preload, radix_tree_preloads) = { 0, };
static inline struct radix_tree_node *entry_to_node(void *ptr)
{
return (void *)((unsigned long)ptr & ~RADIX_TREE_INTERNAL_NODE);
}
static inline void *node_to_entry(void *ptr)
{
return (void *)((unsigned long)ptr | RADIX_TREE_INTERNAL_NODE);
@ -1104,6 +1109,120 @@ static inline void __set_iter_shift(struct radix_tree_iter *iter,
#endif
}
/* Construct iter->tags bit-mask from node->tags[tag] array */
static void set_iter_tags(struct radix_tree_iter *iter,
struct radix_tree_node *node, unsigned offset,
unsigned tag)
{
unsigned tag_long = offset / BITS_PER_LONG;
unsigned tag_bit = offset % BITS_PER_LONG;
iter->tags = node->tags[tag][tag_long] >> tag_bit;
/* This never happens if RADIX_TREE_TAG_LONGS == 1 */
if (tag_long < RADIX_TREE_TAG_LONGS - 1) {
/* Pick tags from next element */
if (tag_bit)
iter->tags |= node->tags[tag][tag_long + 1] <<
(BITS_PER_LONG - tag_bit);
/* Clip chunk size, here only BITS_PER_LONG tags */
iter->next_index = __radix_tree_iter_add(iter, BITS_PER_LONG);
}
}
#ifdef CONFIG_RADIX_TREE_MULTIORDER
static void **skip_siblings(struct radix_tree_node **nodep,
void **slot, struct radix_tree_iter *iter)
{
void *sib = node_to_entry(slot - 1);
while (iter->index < iter->next_index) {
*nodep = rcu_dereference_raw(*slot);
if (*nodep && *nodep != sib)
return slot;
slot++;
iter->index = __radix_tree_iter_add(iter, 1);
iter->tags >>= 1;
}
*nodep = NULL;
return NULL;
}
void ** __radix_tree_next_slot(void **slot, struct radix_tree_iter *iter,
unsigned flags)
{
unsigned tag = flags & RADIX_TREE_ITER_TAG_MASK;
struct radix_tree_node *node = rcu_dereference_raw(*slot);
slot = skip_siblings(&node, slot, iter);
while (radix_tree_is_internal_node(node)) {
unsigned offset;
unsigned long next_index;
if (node == RADIX_TREE_RETRY)
return slot;
node = entry_to_node(node);
iter->shift = node->shift;
if (flags & RADIX_TREE_ITER_TAGGED) {
offset = radix_tree_find_next_bit(node, tag, 0);
if (offset == RADIX_TREE_MAP_SIZE)
return NULL;
slot = &node->slots[offset];
iter->index = __radix_tree_iter_add(iter, offset);
set_iter_tags(iter, node, offset, tag);
node = rcu_dereference_raw(*slot);
} else {
offset = 0;
slot = &node->slots[0];
for (;;) {
node = rcu_dereference_raw(*slot);
if (node)
break;
slot++;
offset++;
if (offset == RADIX_TREE_MAP_SIZE)
return NULL;
}
iter->index = __radix_tree_iter_add(iter, offset);
}
if ((flags & RADIX_TREE_ITER_CONTIG) && (offset > 0))
goto none;
next_index = (iter->index | shift_maxindex(iter->shift)) + 1;
if (next_index < iter->next_index)
iter->next_index = next_index;
}
return slot;
none:
iter->next_index = 0;
return NULL;
}
EXPORT_SYMBOL(__radix_tree_next_slot);
#else
static void **skip_siblings(struct radix_tree_node **nodep,
void **slot, struct radix_tree_iter *iter)
{
return slot;
}
#endif
void **radix_tree_iter_resume(void **slot, struct radix_tree_iter *iter)
{
struct radix_tree_node *node;
slot++;
iter->index = __radix_tree_iter_add(iter, 1);
node = rcu_dereference_raw(*slot);
skip_siblings(&node, slot, iter);
iter->next_index = iter->index;
iter->tags = 0;
return NULL;
}
EXPORT_SYMBOL(radix_tree_iter_resume);
/**
* radix_tree_next_chunk - find next chunk of slots for iteration
*
@ -1191,23 +1310,8 @@ void **radix_tree_next_chunk(struct radix_tree_root *root,
iter->next_index = (index | node_maxindex(node)) + 1;
__set_iter_shift(iter, node->shift);
/* Construct iter->tags bit-mask from node->tags[tag] array */
if (flags & RADIX_TREE_ITER_TAGGED) {
unsigned tag_long, tag_bit;
tag_long = offset / BITS_PER_LONG;
tag_bit = offset % BITS_PER_LONG;
iter->tags = node->tags[tag][tag_long] >> tag_bit;
/* This never happens if RADIX_TREE_TAG_LONGS == 1 */
if (tag_long < RADIX_TREE_TAG_LONGS - 1) {
/* Pick tags from next element */
if (tag_bit)
iter->tags |= node->tags[tag][tag_long + 1] <<
(BITS_PER_LONG - tag_bit);
/* Clip chunk size, here only BITS_PER_LONG tags */
iter->next_index = index + BITS_PER_LONG;
}
}
if (flags & RADIX_TREE_ITER_TAGGED)
set_iter_tags(iter, node, offset, tag);
return node->slots + offset;
}

7
mm/khugepaged.c
View File

@ -1446,7 +1446,7 @@ static void collapse_shmem(struct mm_struct *mm,
radix_tree_replace_slot(&mapping->page_tree, slot,
new_page + (index % HPAGE_PMD_NR));
slot = radix_tree_iter_next(&iter);
slot = radix_tree_iter_resume(slot, &iter);
index++;
continue;
out_lru:
@ -1546,7 +1546,6 @@ tree_unlocked:
/* Put holes back where they were */
radix_tree_delete(&mapping->page_tree,
iter.index);
slot = radix_tree_iter_next(&iter);
continue;
}
@ -1557,11 +1556,11 @@ tree_unlocked:
page_ref_unfreeze(page, 2);
radix_tree_replace_slot(&mapping->page_tree,
slot, page);
slot = radix_tree_iter_resume(slot, &iter);
spin_unlock_irq(&mapping->tree_lock);
putback_lru_page(page);
unlock_page(page);
spin_lock_irq(&mapping->tree_lock);
slot = radix_tree_iter_next(&iter);
}
VM_BUG_ON(nr_none);
spin_unlock_irq(&mapping->tree_lock);
@ -1641,8 +1640,8 @@ static void khugepaged_scan_shmem(struct mm_struct *mm,
present++;
if (need_resched()) {
slot = radix_tree_iter_resume(slot, &iter);
cond_resched_rcu();
slot = radix_tree_iter_next(&iter);
}
}
rcu_read_unlock();

6
mm/shmem.c
View File

@ -661,8 +661,8 @@ unsigned long shmem_partial_swap_usage(struct address_space *mapping,
swapped++;
if (need_resched()) {
slot = radix_tree_iter_resume(slot, &iter);
cond_resched_rcu();
slot = radix_tree_iter_next(&iter);
}
}
@ -2447,8 +2447,8 @@ static void shmem_tag_pins(struct address_space *mapping)
}
if (need_resched()) {
slot = radix_tree_iter_resume(slot, &iter);
cond_resched_rcu();
slot = radix_tree_iter_next(&iter);
}
}
rcu_read_unlock();
@ -2517,8 +2517,8 @@ static int shmem_wait_for_pins(struct address_space *mapping)
spin_unlock_irq(&mapping->tree_lock);
continue_resched:
if (need_resched()) {
slot = radix_tree_iter_resume(slot, &iter);
cond_resched_rcu();
slot = radix_tree_iter_next(&iter);
}
}
rcu_read_unlock();

12
tools/testing/radix-tree/iteration_check.c
View File

@ -48,8 +48,8 @@ static void *add_entries_fn(void *arg)
/*
* Iterate over the tagged entries, doing a radix_tree_iter_retry() as we find
* things that have been removed and randomly resetting our iteration to the
* next chunk with radix_tree_iter_next(). Both radix_tree_iter_retry() and
* radix_tree_iter_next() cause radix_tree_next_slot() to be called with a
* next chunk with radix_tree_iter_resume(). Both radix_tree_iter_retry() and
* radix_tree_iter_resume() cause radix_tree_next_slot() to be called with a
* NULL 'slot' variable.
*/
static void *tagged_iteration_fn(void *arg)
@ -79,7 +79,7 @@ static void *tagged_iteration_fn(void *arg)
}
if (rand_r(&seeds[0]) % 50 == 0) {
slot = radix_tree_iter_next(&iter);
slot = radix_tree_iter_resume(slot, &iter);
rcu_read_unlock();
rcu_barrier();
rcu_read_lock();
@ -96,8 +96,8 @@ static void *tagged_iteration_fn(void *arg)
/*
* Iterate over the entries, doing a radix_tree_iter_retry() as we find things
* that have been removed and randomly resetting our iteration to the next
* chunk with radix_tree_iter_next(). Both radix_tree_iter_retry() and
* radix_tree_iter_next() cause radix_tree_next_slot() to be called with a
* chunk with radix_tree_iter_resume(). Both radix_tree_iter_retry() and
* radix_tree_iter_resume() cause radix_tree_next_slot() to be called with a
* NULL 'slot' variable.
*/
static void *untagged_iteration_fn(void *arg)
@ -127,7 +127,7 @@ static void *untagged_iteration_fn(void *arg)
}
if (rand_r(&seeds[1]) % 50 == 0) {
slot = radix_tree_iter_next(&iter);
slot = radix_tree_iter_resume(slot, &iter);
rcu_read_unlock();
rcu_barrier();
rcu_read_lock();

28
tools/testing/radix-tree/multiorder.c
View File

@ -231,11 +231,14 @@ void multiorder_iteration(void)
radix_tree_for_each_slot(slot, &tree, &iter, j) {
int height = order[i] / RADIX_TREE_MAP_SHIFT;
int shift = height * RADIX_TREE_MAP_SHIFT;
int mask = (1 << order[i]) - 1;
unsigned long mask = (1UL << order[i]) - 1;
struct item *item = *slot;
assert(iter.index >= (index[i] &~ mask));
assert(iter.index <= (index[i] | mask));
assert((iter.index | mask) == (index[i] | mask));
assert(iter.shift == shift);
assert(!radix_tree_is_internal_node(item));
assert((item->index | mask) == (index[i] | mask));
assert(item->order == order[i]);
i++;
}
}
@ -269,7 +272,7 @@ void multiorder_tagged_iteration(void)
assert(radix_tree_tag_set(&tree, tag_index[i], 1));
for (j = 0; j < 256; j++) {
int mask, k;
int k;
for (i = 0; i < TAG_ENTRIES; i++) {
for (k = i; index[k] < tag_index[i]; k++)
@ -279,12 +282,16 @@ void multiorder_tagged_iteration(void)
}
radix_tree_for_each_tagged(slot, &tree, &iter, j, 1) {
unsigned long mask;
struct item *item = *slot;
for (k = i; index[k] < tag_index[i]; k++)
;
mask = (1 << order[k]) - 1;
mask = (1UL << order[k]) - 1;
assert(iter.index >= (tag_index[i] &~ mask));
assert(iter.index <= (tag_index[i] | mask));
assert((iter.index | mask) == (tag_index[i] | mask));
assert(!radix_tree_is_internal_node(item));
assert((item->index | mask) == (tag_index[i] | mask));
assert(item->order == order[k]);
i++;
}
}
@ -303,12 +310,15 @@ void multiorder_tagged_iteration(void)
}
radix_tree_for_each_tagged(slot, &tree, &iter, j, 2) {
struct item *item = *slot;
for (k = i; index[k] < tag_index[i]; k++)
;
mask = (1 << order[k]) - 1;
assert(iter.index >= (tag_index[i] &~ mask));
assert(iter.index <= (tag_index[i] | mask));
assert((iter.index | mask) == (tag_index[i] | mask));
assert(!radix_tree_is_internal_node(item));
assert((item->index | mask) == (tag_index[i] | mask));
assert(item->order == order[k]);
i++;
}
}

8
tools/testing/radix-tree/regression3.c
View File

@ -5,7 +5,7 @@
* In following radix_tree_next_slot current chunk size becomes zero.
* This isn't checked and it tries to dereference null pointer in slot.
*
* Helper radix_tree_iter_next reset slot to NULL and next_index to index + 1,
* Helper radix_tree_iter_resume reset slot to NULL and next_index to index + 1,
* for tagger iteraction it also must reset cached tags in iterator to abort
* next radix_tree_next_slot and go to slow-path into radix_tree_next_chunk.
*
@ -88,7 +88,7 @@ void regression3_test(void)
printf("slot %ld %p\n", iter.index, *slot);
if (!iter.index) {
printf("next at %ld\n", iter.index);
slot = radix_tree_iter_next(&iter);
slot = radix_tree_iter_resume(slot, &iter);
}
}
@ -96,7 +96,7 @@ void regression3_test(void)
printf("contig %ld %p\n", iter.index, *slot);
if (!iter.index) {
printf("next at %ld\n", iter.index);
slot = radix_tree_iter_next(&iter);
slot = radix_tree_iter_resume(slot, &iter);
}
}
@ -106,7 +106,7 @@ void regression3_test(void)
printf("tagged %ld %p\n", iter.index, *slot);
if (!iter.index) {
printf("next at %ld\n", iter.index);
slot = radix_tree_iter_next(&iter);
slot = radix_tree_iter_resume(slot, &iter);
}
}

1
tools/testing/radix-tree/test.h
View File

@ -41,6 +41,7 @@ void verify_tag_consistency(struct radix_tree_root *root, unsigned int tag);
extern int nr_allocated;
/* Normally private parts of lib/radix-tree.c */
struct radix_tree_node *entry_to_node(void *ptr);
void radix_tree_dump(struct radix_tree_root *root);
int root_tag_get(struct radix_tree_root *root, unsigned int tag);
unsigned long node_maxindex(struct radix_tree_node *);