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authorHugh Dickins <hughd@google.com>2014-07-23 14:00:15 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2014-07-23 15:10:55 -0700
commit792ceaefe62189e3beea612ec0a052e42a81e993 (patch)
tree7935c92dde542169bc089f64627e09336785cf56 /mm/truncate.c
parentb1a366500bd537b50c3aad26dc7df083ec03a448 (diff)
mm/fs: fix pessimization in hole-punching pagecache
I wanted to revert my v3.1 commit d0823576bf4b ("mm: pincer in truncate_inode_pages_range"), to keep truncate_inode_pages_range() in synch with shmem_undo_range(); but have stepped back - a change to hole-punching in truncate_inode_pages_range() is a change to hole-punching in every filesystem (except tmpfs) that supports it. If there's a logical proof why no filesystem can depend for its own correctness on the pincer guarantee in truncate_inode_pages_range() - an instant when the entire hole is removed from pagecache - then let's revisit later. But the evidence is that only tmpfs suffered from the livelock, and we have no intention of extending hole-punch to ramfs. So for now just add a few comments (to match or differ from those in shmem_undo_range()), and fix one silliness noticed in d0823576bf4b... Its "index == start" addition to the hole-punch termination test was incomplete: it opened a way for the end condition to be missed, and the loop go on looking through the radix_tree, all the way to end of file. Fix that pessimization by resetting index when detected in inner loop. Note that it's actually hard to hit this case, without the obsessive concurrent faulting that trinity does: normally all pages are removed in the initial trylock_page() pass, and this loop finds nothing to do. I had to "#if 0" out the initial pass to reproduce bug and test fix. Signed-off-by: Hugh Dickins <hughd@google.com> Cc: Sasha Levin <sasha.levin@oracle.com> Cc: Konstantin Khlebnikov <koct9i@gmail.com> Cc: Lukas Czerner <lczerner@redhat.com> Cc: Dave Jones <davej@redhat.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/truncate.c')
-rw-r--r--mm/truncate.c11
1 files changed, 8 insertions, 3 deletions
diff --git a/mm/truncate.c b/mm/truncate.c
index 6a78c814bebf..eda247307164 100644
--- a/mm/truncate.c
+++ b/mm/truncate.c
@@ -355,14 +355,16 @@ void truncate_inode_pages_range(struct address_space *mapping,
for ( ; ; ) {
cond_resched();
if (!pagevec_lookup_entries(&pvec, mapping, index,
- min(end - index, (pgoff_t)PAGEVEC_SIZE),
- indices)) {
+ min(end - index, (pgoff_t)PAGEVEC_SIZE), indices)) {
+ /* If all gone from start onwards, we're done */
if (index == start)
break;
+ /* Otherwise restart to make sure all gone */
index = start;
continue;
}
if (index == start && indices[0] >= end) {
+ /* All gone out of hole to be punched, we're done */
pagevec_remove_exceptionals(&pvec);
pagevec_release(&pvec);
break;
@@ -373,8 +375,11 @@ void truncate_inode_pages_range(struct address_space *mapping,
/* We rely upon deletion not changing page->index */
index = indices[i];
- if (index >= end)
+ if (index >= end) {
+ /* Restart punch to make sure all gone */
+ index = start - 1;
break;
+ }
if (radix_tree_exceptional_entry(page)) {
clear_exceptional_entry(mapping, index, page);

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