The patch titled writeback: avoid livelocking WB_SYNC_ALL writeback has been removed from the -mm tree. Its filename was writeback-avoid-livelocking-wb_sync_all-writeback.patch This patch was dropped because it was merged into mainline or a subsystem tree The current -mm tree may be found at http://userweb.kernel.org/~akpm/mmotm/ ------------------------------------------------------ Subject: writeback: avoid livelocking WB_SYNC_ALL writeback From: Jan Kara <jack@xxxxxxx> When wb_writeback() is called in WB_SYNC_ALL mode, work->nr_to_write is usually set to LONG_MAX. The logic in wb_writeback() then calls __writeback_inodes_sb() with nr_to_write == MAX_WRITEBACK_PAGES and we easily end up with non-positive nr_to_write after the function returns, if the inode has more than MAX_WRITEBACK_PAGES dirty pages at the moment. When nr_to_write is <= 0 wb_writeback() decides we need another round of writeback but this is wrong in some cases! For example when a single large file is continuously dirtied, we would never finish syncing it because each pass would be able to write MAX_WRITEBACK_PAGES and inode dirty timestamp never gets updated (as inode is never completely clean). Thus __writeback_inodes_sb() would write the redirtied inode again and again. Fix the issue by setting nr_to_write to LONG_MAX in WB_SYNC_ALL mode. We do not need nr_to_write in WB_SYNC_ALL mode anyway since write_cache_pages() does livelock avoidance using page tagging in WB_SYNC_ALL mode. This makes wb_writeback() call __writeback_inodes_sb() only once on WB_SYNC_ALL. The latter function won't livelock because it works on - a finite set of files by doing queue_io() once at the beginning - a finite set of pages by PAGECACHE_TAG_TOWRITE page tagging After this patch, program from http://lkml.org/lkml/2010/10/24/154 is no longer able to stall sync forever. [fengguang.wu@xxxxxxxxx: fix locking comment] Signed-off-by: Jan Kara <jack@xxxxxxx> Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx> Cc: Johannes Weiner <hannes@xxxxxxxxxxx> Cc: Dave Chinner <david@xxxxxxxxxxxxx> Cc: Christoph Hellwig <hch@xxxxxx> Cc: Jan Engelhardt <jengelh@xxxxxxxxxx> Cc: Jens Axboe <axboe@xxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- fs/fs-writeback.c | 27 +++++++++++++++++++++++---- 1 file changed, 23 insertions(+), 4 deletions(-) diff -puN fs/fs-writeback.c~writeback-avoid-livelocking-wb_sync_all-writeback fs/fs-writeback.c --- a/fs/fs-writeback.c~writeback-avoid-livelocking-wb_sync_all-writeback +++ a/fs/fs-writeback.c @@ -630,6 +630,7 @@ static long wb_writeback(struct bdi_writ }; unsigned long oldest_jif; long wrote = 0; + long write_chunk; struct inode *inode; if (wbc.for_kupdate) { @@ -642,6 +643,24 @@ static long wb_writeback(struct bdi_writ wbc.range_end = LLONG_MAX; } + /* + * WB_SYNC_ALL mode does livelock avoidance by syncing dirty + * inodes/pages in one big loop. Setting wbc.nr_to_write=LONG_MAX + * here avoids calling into writeback_inodes_wb() more than once. + * + * The intended call sequence for WB_SYNC_ALL writeback is: + * + * wb_writeback() + * __writeback_inodes_sb() <== called only once + * write_cache_pages() <== called once for each inode + * (quickly) tag currently dirty pages + * (maybe slowly) sync all tagged pages + */ + if (wbc.sync_mode == WB_SYNC_NONE) + write_chunk = MAX_WRITEBACK_PAGES; + else + write_chunk = LONG_MAX; + wbc.wb_start = jiffies; /* livelock avoidance */ for (;;) { /* @@ -668,7 +687,7 @@ static long wb_writeback(struct bdi_writ break; wbc.more_io = 0; - wbc.nr_to_write = MAX_WRITEBACK_PAGES; + wbc.nr_to_write = write_chunk; wbc.pages_skipped = 0; trace_wbc_writeback_start(&wbc, wb->bdi); @@ -678,8 +697,8 @@ static long wb_writeback(struct bdi_writ writeback_inodes_wb(wb, &wbc); trace_wbc_writeback_written(&wbc, wb->bdi); - work->nr_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write; - wrote += MAX_WRITEBACK_PAGES - wbc.nr_to_write; + work->nr_pages -= write_chunk - wbc.nr_to_write; + wrote += write_chunk - wbc.nr_to_write; /* * If we consumed everything, see if we have more @@ -694,7 +713,7 @@ static long wb_writeback(struct bdi_writ /* * Did we write something? Try for more */ - if (wbc.nr_to_write < MAX_WRITEBACK_PAGES) + if (wbc.nr_to_write < write_chunk) continue; /* * Nothing written. Wait for some inode to _ Patches currently in -mm which might be from jack@xxxxxxx are origin.patch linux-next.patch writeback-check-skipped-pages-on-wb_sync_all.patch writeback-check-skipped-pages-on-wb_sync_all-update.patch writeback-check-skipped-pages-on-wb_sync_all-update-fix.patch writeback-io-less-balance_dirty_pages.patch writeback-consolidate-variable-names-in-balance_dirty_pages.patch writeback-per-task-rate-limit-on-balance_dirty_pages.patch writeback-per-task-rate-limit-on-balance_dirty_pages-fix.patch writeback-prevent-duplicate-balance_dirty_pages_ratelimited-calls.patch writeback-account-per-bdi-accumulated-written-pages.patch writeback-bdi-write-bandwidth-estimation.patch writeback-bdi-write-bandwidth-estimation-fix.patch writeback-show-bdi-write-bandwidth-in-debugfs.patch writeback-quit-throttling-when-bdi-dirty-pages-dropped-low.patch writeback-reduce-per-bdi-dirty-threshold-ramp-up-time.patch writeback-make-reasonable-gap-between-the-dirty-background-thresholds.patch writeback-scale-down-max-throttle-bandwidth-on-concurrent-dirtiers.patch writeback-add-trace-event-for-balance_dirty_pages.patch writeback-make-nr_to_write-a-per-file-limit.patch writeback-make-nr_to_write-a-per-file-limit-fix.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html