From 5b41d92437f1ae19b3f3ffa3b16589fd5df50ac0 Mon Sep 17 00:00:00 2001 From: Eric Sandeen Date: Wed, 27 Oct 2010 21:30:13 -0400 Subject: [PATCH] ext4: implement writeback livelock avoidance using page tagging This is analogous to Jan Kara's commit, f446daaea9d4a420d16c606f755f3689dcb2d0ce mm: implement writeback livelock avoidance using page tagging but since we forked write_cache_pages, we need to reimplement it there (and in ext4_da_writepages, since range_cyclic handling was moved to there) If you start a large buffered IO to a file, and then set fsync after it, you'll find that fsync does not complete until the other IO stops. If you continue re-dirtying the file (say, putting dd with conv=notrunc in a loop), when fsync finally completes (after all IO is done), it reports via tracing that it has written many more pages than the file contains; in other words it has synced and re-synced pages in the file multiple times. This then leads to problems with our writeback_index update, since it advances it by pages written, and essentially sets writeback_index off the end of the file... With the following patch, we only sync as much as was dirty at the time of the sync. Signed-off-by: Eric Sandeen Signed-off-by: "Theodore Ts'o" --- fs/ext4/inode.c | 18 +++++++++++++++--- include/linux/writeback.h | 2 ++ 2 files changed, 17 insertions(+), 3 deletions(-) diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c index 6671fcbb5293..c9ea95ba5fde 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c @@ -2809,16 +2809,21 @@ static int write_cache_pages_da(struct address_space *mapping, pgoff_t index; pgoff_t end; /* Inclusive */ long nr_to_write = wbc->nr_to_write; + int tag; pagevec_init(&pvec, 0); index = wbc->range_start >> PAGE_CACHE_SHIFT; end = wbc->range_end >> PAGE_CACHE_SHIFT; + if (wbc->sync_mode == WB_SYNC_ALL) + tag = PAGECACHE_TAG_TOWRITE; + else + tag = PAGECACHE_TAG_DIRTY; + while (!done && (index <= end)) { int i; - nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, - PAGECACHE_TAG_DIRTY, + nr_pages = pagevec_lookup_tag(&pvec, mapping, &index, tag, min(end - index, (pgoff_t)PAGEVEC_SIZE-1) + 1); if (nr_pages == 0) break; @@ -2923,6 +2928,7 @@ static int ext4_da_writepages(struct address_space *mapping, long desired_nr_to_write, nr_to_writebump = 0; loff_t range_start = wbc->range_start; struct ext4_sb_info *sbi = EXT4_SB(mapping->host->i_sb); + pgoff_t end; trace_ext4_da_writepages(inode, wbc); @@ -2958,8 +2964,11 @@ static int ext4_da_writepages(struct address_space *mapping, wbc->range_start = index << PAGE_CACHE_SHIFT; wbc->range_end = LLONG_MAX; wbc->range_cyclic = 0; - } else + end = -1; + } else { index = wbc->range_start >> PAGE_CACHE_SHIFT; + end = wbc->range_end >> PAGE_CACHE_SHIFT; + } /* * This works around two forms of stupidity. The first is in @@ -3000,6 +3009,9 @@ static int ext4_da_writepages(struct address_space *mapping, pages_skipped = wbc->pages_skipped; retry: + if (wbc->sync_mode == WB_SYNC_ALL) + tag_pages_for_writeback(mapping, index, end); + while (!ret && wbc->nr_to_write > 0) { /* diff --git a/include/linux/writeback.h b/include/linux/writeback.h index 72a5d647a5f2..3d132bfb4f3d 100644 --- a/include/linux/writeback.h +++ b/include/linux/writeback.h @@ -143,6 +143,8 @@ typedef int (*writepage_t)(struct page *page, struct writeback_control *wbc, int generic_writepages(struct address_space *mapping, struct writeback_control *wbc); +void tag_pages_for_writeback(struct address_space *mapping, + pgoff_t start, pgoff_t end); int write_cache_pages(struct address_space *mapping, struct writeback_control *wbc, writepage_t writepage, void *data); -- 2.20.1