From 148deab223b23734069abcacb5c7118b0e7deadc Mon Sep 17 00:00:00 2001 From: Matthew Wilcox Date: Wed, 14 Dec 2016 15:08:49 -0800 Subject: 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 Tested-by: Kirill A. Shutemov Cc: Konstantin Khlebnikov Cc: Ross Zwisler Cc: Matthew Wilcox Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- tools/testing/radix-tree/regression3.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) (limited to 'tools/testing/radix-tree/regression3.c') diff --git a/tools/testing/radix-tree/regression3.c b/tools/testing/radix-tree/regression3.c index 1f06ed73d0a8..b594841fae85 100644 --- a/tools/testing/radix-tree/regression3.c +++ b/tools/testing/radix-tree/regression3.c @@ -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); } } -- cgit v1.2.3-70-g09d2