From: Chao Yu <chao@kernel.org>
To: Jaegeuk Kim <jaegeuk@kernel.org>, Chao Yu <yuchao0@huawei.com>
Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-f2fs-devel@lists.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH] f2fs: merge WRITE bio into previous WRITE_SYNC
Date: Wed, 7 Sep 2016 22:12:17 +0800 [thread overview]
Message-ID: <9c35b994-620f-b633-f3db-4e0622f09cd7@kernel.org> (raw)
In-Reply-To: <20160902183658.GA917@jaegeuk>
On 2016/9/3 2:36, Jaegeuk Kim wrote:
> On Fri, Sep 02, 2016 at 03:33:33PM +0800, Chao Yu wrote:
>> Hi Jaegeuk,
>>
>> On 2016/8/27 8:53, Jaegeuk Kim wrote:
>>> This can avoid bio splits due to different op_flags.
>>
>> I thought about this, but I think this is not a good idea to increase merging
>> ratio of pages in bio. It breaks the rule of SYNC/ASYNC IO defined by system
>> which indicate degree of IO emergency, finally, some/more non-emergent IO will
>> treated as emergent one by IO scheduler, it will interrupt SYNC IOs in block
>> layer, more seriously, it may make real SYNC IO starvation.
>
> I understand your concern.
> Originally, I tried to avoid breaking a big WRITE_SYNC by a small number of
Hmm.. I'm worry about the opposite case: user triggers small WRITE_SYNC IO
periodically, meanwhile there are big number of WRITE, with our new approach,
actually we will increase the number of synchronous WRITE IO obviously because
we will mix ASYNC/SYNC WRITE into bio cache intensively more than before since
we drop writepages mutexlock. So I'm afread the result is that it will mislead
scheduling of block layer.
> WRITE. And, I thought new WRITE can be piggybacked into previous WRITE_SYNC.
>
> IMO, this happens very occassionally since previous pending bio should be
> WRITE_SYNC while a new request is WRITE. Even if this happens, the piggybacked
> size would not exceed over bio's max pages.
> If lots of WRITE come, we won't change at all.
I thinks this is related to writeback / blocklayer / cgroup subsystem which use
this tag frequently, maybe we should Cc their's mailing list for more opinion...
What's your opinion? :)
thanks,
>
> Thanks,
>
>>
>> Thanks,
>>
>>>
>>> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
>>> ---
>>> fs/f2fs/data.c | 5 +++++
>>> 1 file changed, 5 insertions(+)
>>>
>>> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
>>> index 7c8e219..c7c2022 100644
>>> --- a/fs/f2fs/data.c
>>> +++ b/fs/f2fs/data.c
>>> @@ -267,6 +267,11 @@ void f2fs_submit_page_mbio(struct f2fs_io_info *fio)
>>>
>>> down_write(&io->io_rwsem);
>>>
>>> + /* WRITE can be merged into previous WRITE_SYNC */
>>> + if (io->bio && io->last_block_in_bio == fio->new_blkaddr - 1 &&
>>> + io->fio.op == fio->op && io->fio.op_flags == WRITE_SYNC)
>>> + fio->op_flags = WRITE_SYNC;
>>> +
>>> if (io->bio && (io->last_block_in_bio != fio->new_blkaddr - 1 ||
>>> (io->fio.op != fio->op || io->fio.op_flags != fio->op_flags)))
>>> __submit_merged_bio(io);
>>>
>
> ------------------------------------------------------------------------------
> _______________________________________________
> Linux-f2fs-devel mailing list
> Linux-f2fs-devel@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
>
next prev parent reply other threads:[~2016-09-07 14:12 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-27 0:53 [PATCH] f2fs: merge WRITE bio into previous WRITE_SYNC Jaegeuk Kim
2016-09-02 7:33 ` Chao Yu
2016-09-02 18:36 ` Jaegeuk Kim
2016-09-07 14:12 ` Chao Yu [this message]
2016-09-08 0:26 ` [f2fs-dev] " Jaegeuk Kim
2016-09-08 16:09 ` Chao Yu
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