Messages in this thread Patches in this message | | | Date | Fri, 12 Feb 2010 10:16:09 +0100 | From | Jens Axboe <> | Subject | [PATCH] writeback: Fix broken sync writeback |
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Hi,
There's currently a writeback bug in the 2.6.32 and 2.6.33-rc kernels that prevent proper writeback when sync(1) is being run. Instead of flushing everything older than the sync run, it will do chunks of normal MAX_WRITEBACK_PAGES writeback and restart over and over. This results in very suboptimal writeback for many files, see the initial report from Jan Engelhardt:
http://lkml.org/lkml/2010/1/22/382
This fixes it by using the passed in page writeback count, instead of doing MAX_WRITEBACK_PAGES batches, which gets us much better performance (Jan reports it's up from ~400KB/sec to 10MB/sec) and makes sync(1) finish properly even when new pages are being dirted.
Thanks to Jan Kara <jack@suse.cz> for spotting this problem!
Cc: stable@kernel.org Reported-by: Jan Engelhardt <jengelh@medozas.de> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
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I'm sending this out as a patch on the list instead since I'll be going away for a week skiing very shortly, a mail+patch is easier to discuss here.
Greg, I'm attaching a 2.6.32 based patch as well, since this one will not apply to 2.6.32.
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index 1a7c42c..55aeea9 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -749,6 +749,8 @@ static long wb_writeback(struct bdi_writeback *wb, } for (;;) { + long to_write = 0; + /* * Stop writeback when nr_pages has been consumed */ @@ -762,12 +764,17 @@ static long wb_writeback(struct bdi_writeback *wb, if (args->for_background && !over_bground_thresh()) break; + if (args->sync_mode == WB_SYNC_ALL) + to_write = args->nr_pages; + if (!to_write) + to_write = MAX_WRITEBACK_PAGES; + wbc.more_io = 0; - wbc.nr_to_write = MAX_WRITEBACK_PAGES; + wbc.nr_to_write = to_write; wbc.pages_skipped = 0; writeback_inodes_wb(wb, &wbc); - args->nr_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write; - wrote += MAX_WRITEBACK_PAGES - wbc.nr_to_write; + args->nr_pages -= to_write - wbc.nr_to_write; + wrote += to_write - wbc.nr_to_write; /* * If we consumed everything, see if we have more @@ -782,7 +789,7 @@ static long wb_writeback(struct bdi_writeback *wb, /* * Did we write something? Try for more */ - if (wbc.nr_to_write < MAX_WRITEBACK_PAGES) + if (wbc.nr_to_write < to_write) continue; /* * Nothing written. Wait for some inode to -- Jens Axboe
commit 057226ca7447880e4e766a82cf32197e492ba963 Author: Jens Axboe <jens.axboe@oracle.com> Date: Fri Feb 12 10:14:34 2010 +0100
writeback: Fix broken sync writeback
There's currently a writeback bug in the 2.6.32 and 2.6.33-rc kernels that prevent proper writeback when sync(1) is being run. Instead of flushing everything older than the sync run, it will do chunks of normal MAX_WRITEBACK_PAGES writeback and restart over and over. This results in very suboptimal writeback for many files, see the initial report from Jan Engelhardt:
http://lkml.org/lkml/2010/1/22/382
This fixes it by using the passed in page writeback count, instead of doing MAX_WRITEBACK_PAGES batches, which gets us much better performance (Jan reports it's up from ~400KB/sec to 10MB/sec) and makes sync(1) finish properly even when new pages are being dirted.
Thanks to Jan Kara <jack@suse.cz> for spotting this problem!
Cc: stable@kernel.org Reported-by: Jan Engelhardt <jengelh@medozas.de> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index 9d5360c..8a46c67 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -773,6 +773,8 @@ static long wb_writeback(struct bdi_writeback *wb, } for (;;) { + long to_write = 0; + /* * Stop writeback when nr_pages has been consumed */ @@ -786,13 +788,18 @@ static long wb_writeback(struct bdi_writeback *wb, if (args->for_background && !over_bground_thresh()) break; + if (args->sync_mode == WB_SYNC_ALL) + to_write = args->nr_pages; + if (!to_write) + to_write = MAX_WRITEBACK_PAGES; + wbc.more_io = 0; wbc.encountered_congestion = 0; - wbc.nr_to_write = MAX_WRITEBACK_PAGES; + wbc.nr_to_write = to_write; wbc.pages_skipped = 0; writeback_inodes_wb(wb, &wbc); - args->nr_pages -= MAX_WRITEBACK_PAGES - wbc.nr_to_write; - wrote += MAX_WRITEBACK_PAGES - wbc.nr_to_write; + args->nr_pages -= to_write - wbc.nr_to_write; + wrote += to_write - wbc.nr_to_write; /* * If we consumed everything, see if we have more @@ -807,7 +814,7 @@ static long wb_writeback(struct bdi_writeback *wb, /* * Did we write something? Try for more */ - if (wbc.nr_to_write < MAX_WRITEBACK_PAGES) + if (wbc.nr_to_write < to_write) continue; /* * Nothing written. Wait for some inode to | |