Messages in this thread | | | Date | Sun, 27 Sep 2009 18:44:32 +0200 | From | Jens Axboe <> | Subject | Re: [PATCH] bdi_sync_writeback should WB_SYNC_NONE first |
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On Sun, Sep 27 2009, Andrew Morton wrote: > On Fri, 25 Sep 2009 10:10:14 -0400 Chris Mason <chris.mason@oracle.com> wrote: > > > diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c > > index 8e1e5e1..27f8e0e 100644 > > --- a/fs/fs-writeback.c > > +++ b/fs/fs-writeback.c > > @@ -225,7 +225,7 @@ static void bdi_sync_writeback(struct backing_dev_info *bdi, > > { > > struct wb_writeback_args args = { > > .sb = sb, > > - .sync_mode = WB_SYNC_ALL, > > + .sync_mode = WB_SYNC_NONE, > > .nr_pages = LONG_MAX, > > .range_cyclic = 0, > > }; > > @@ -236,6 +236,13 @@ static void bdi_sync_writeback(struct backing_dev_info *bdi, > > > > bdi_queue_work(bdi, &work); > > bdi_wait_on_work_clear(&work); > > + > > + args.sync_mode = WB_SYNC_ALL; > > + args.nr_pages = LONG_MAX; > > + > > + work.state = WS_USED | WS_ONSTACK; > > + bdi_queue_work(bdi, &work); > > + bdi_wait_on_work_clear(&work); > > } > > Those LONG_MAX's are a worry. What prevents a very long > almost-livelock from occurring if userspace is concurrently dirtying > pagecache at a high rate?
Not sure whether Chris' system is back up again, but I discussed this with him on irc. Since the WB_SYNC_ALL writeback should be queued behind the WB_SYNC_NONE that the non-wait sync already issued, not sure why this patch makes a difference. It's definitely not the right approach.
I'll debug this when I get back.
-- Jens Axboe
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