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

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Date:   Mon, 9 Oct 2017 18:44:23 +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 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.

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

Thanks
Yafang