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radix-tree: improve multiorder iterators

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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>
This commit is contained in:
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
Download patch file Download diff file Expand all files Collapse all files

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 */