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

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Date:   Mon, 9 Oct 2017 19:36:48 +0800
From:   Yafang Shao <laoar.shao@...il.com>
To:     Jan Kara <jack@...e.cz>
Cc:     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

2017-10-09 19:03 GMT+08:00 Jan Kara <jack@...e.cz>:
> 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.
>

Got it!
I will implement it base on this branch.

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

Thanks
Yafang