linux-kernel - Re: [PATCH] mm/page-writeback.c: fix bug caused by disable periodic writeback

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Message-ID: <20171009110332.GG17917@quack2.suse.cz>
Date:   Mon, 9 Oct 2017 13:03:32 +0200
From:   Jan Kara <jack@...e.cz>
To:     Yafang Shao <laoar.shao@...il.com>
Cc:     Jan Kara <jack@...e.cz>, Andrew Morton <akpm@...ux-foundation.org>,
        mhocko@...e.com, Johannes Weiner <hannes@...xchg.org>,
        vdavydov.dev@...il.com, jlayton@...hat.com, nborisov@...e.com,
        Theodore Ts'o <tytso@....edu>, mawilcox@...rosoft.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org, axboe@...nel.dk
Subject: Re: [PATCH] mm/page-writeback.c: fix bug caused by disable periodic
 writeback

On Mon 09-10-17 18:44:23, Yafang Shao wrote:
> 2017-10-09 17:56 GMT+08:00 Jan Kara <jack@...e.cz>:
> > On Sat 07-10-17 06:58:04, Yafang Shao wrote:
> >> After disable periodic writeback by writing 0 to
> >> dirty_writeback_centisecs, the handler wb_workfn() will not be
> >> entered again until the dirty background limit reaches or
> >> sync syscall is executed or no enough free memory available or
> >> vmscan is triggered.
> >> So the periodic writeback can't be enabled by writing a non-zero
> >> value to dirty_writeback_centisecs
> >> As it can be disabled by sysctl, it should be able to enable by
> >> sysctl as well.
> >>
> >> Signed-off-by: Yafang Shao <laoar.shao@...il.com>
> >> ---
> >>  mm/page-writeback.c | 8 +++++++-
> >>  1 file changed, 7 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> >> index 0b9c5cb..e202f37 100644
> >> --- a/mm/page-writeback.c
> >> +++ b/mm/page-writeback.c
> >> @@ -1972,7 +1972,13 @@ bool wb_over_bg_thresh(struct bdi_writeback *wb)
> >>  int dirty_writeback_centisecs_handler(struct ctl_table *table, int write,
> >>       void __user *buffer, size_t *length, loff_t *ppos)
> >>  {
> >> -     proc_dointvec(table, write, buffer, length, ppos);
> >> +     unsigned int old_interval = dirty_writeback_interval;
> >> +     int ret;
> >> +
> >> +     ret = proc_dointvec(table, write, buffer, length, ppos);
> >> +     if (!ret && !old_interval && dirty_writeback_interval)
> >> +             wakeup_flusher_threads(0, WB_REASON_PERIODIC);
> >> +
> >
> > I agree it is good to schedule some writeback. However Jens has some
> > changes queued in linux-block tree in this area so your change won't apply.
> > So please base your changes on his tree.
> >
> 
> Do you mean this tree
> git://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git ?
> 
> I have checked his tree and find nothing need to change on my patch.

Yes, I mean that tree. Check the wb_start_all branch.

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR