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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

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);
}
}