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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
tools/testing/radix-tree/iteration_check.c
+6 -6
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();