Commit c10f778d authored Sep 06, 2017 by Jan Kara Committed by Linus Torvalds Sep 06, 2017

fs: fix performance regression in clean_bdev_aliases()

Commit e64855c6 ("fs: Add helper to clean bdev aliases under a bh
and use it") added a wrapper for clean_bdev_aliases() that invalidates
bdev aliases underlying a single buffer head.

However this has caused a performance regression for bonnie++ benchmark
on ext4 filesystem when delayed allocation is turned off (ext3 mode) -
average of 3 runs:

  Hmean SeqOut Char  164787.55 (  0.00%) 107189.06 (-34.95%)
  Hmean SeqOut Block 219883.89 (  0.00%) 168870.32 (-23.20%)

The reason for this regression is that clean_bdev_aliases() is slower
when called for a single block because pagevec_lookup() it uses will end
up iterating through the radix tree until it finds a page (which may
take a while) but we are only interested whether there's a page at a
particular index.

Fix the problem by using pagevec_lookup_range() instead which avoids the
needless iteration.

Fixes: e64855c6 ("fs: Add helper to clean bdev aliases under a bh and use it")
Link: http://lkml.kernel.org/r/20170726114704.7626-5-jack@suse.cz


Signed-off-by: Jan Kara <jack@suse.cz>
Cc: Jens Axboe <axboe@fb.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent b947cee4

fs/buffer.c

+8 −6

Original line number	Diff line number	Diff line
		@@ -1627,19 +1627,18 @@ void clean_bdev_aliases(struct block_device *bdev, sector_t block, sector_t len)
		struct pagevec pvec;
		pgoff_t index = block >> (PAGE_SHIFT - bd_inode->i_blkbits);
		pgoff_t end;
		int i;
		int i, count;
		struct buffer_head *bh;
		struct buffer_head *head;

		end = (block + len - 1) >> (PAGE_SHIFT - bd_inode->i_blkbits);
		pagevec_init(&pvec, 0);
		while (index <= end && pagevec_lookup(&pvec, bd_mapping, &index,
		min(end - index, (pgoff_t)PAGEVEC_SIZE - 1) + 1)) {
		for (i = 0; i < pagevec_count(&pvec); i++) {
		while (pagevec_lookup_range(&pvec, bd_mapping, &index, end,
		PAGEVEC_SIZE)) {
		count = pagevec_count(&pvec);
		for (i = 0; i < count; i++) {
		struct page *page = pvec.pages[i];

		if (page->index > end)
		break;
		if (!page_has_buffers(page))
		continue;
		/*
		@@ -1669,6 +1668,9 @@ unlock_page:
		}
		pagevec_release(&pvec);
		cond_resched();
		/* End of range already reached? */
		if (index > end \|\| !index)
		break;
		}
		}
		EXPORT_SYMBOL(clean_bdev_aliases);

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