linux-kernel - Re: [f2fs-dev] [PATCH] f2fs: use bio count instead of F2FS

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Message-ID: <3a7e2bf6-fc6e-db09-9b3d-7cdd717d4560@kernel.org>
Date:	Sun, 22 May 2016 21:10:01 +0800
From:	Chao Yu <chao@...nel.org>
To:	Jaegeuk Kim <jaegeuk@...nel.org>, Chao Yu <yuchao0@...wei.com>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH] f2fs: use bio count instead of F2FS_WRITEBACK
 page count

On 2016/5/18 9:31, Jaegeuk Kim wrote:
> On Wed, May 18, 2016 at 09:17:00AM +0800, Chao Yu wrote:
>> Hi Jaegeuk,
>>
>> On 2016/5/18 8:44, Jaegeuk Kim wrote:
>>> This can reduce page counting overhead.
>>
>> We change to increase one reference for one bio, but block layer can split or
>> merge bios by itself, and write_end will be called per bio, so the reference may
>> be maintained incorrectly?
> 
> Well, block layer will merge bios in a same request, and then finally call
> end_io for each original bios, no?

Sorry for the delay, I agree with you that end_io will be called for each bios
in the merging case, and for the spliting case, IIUC, splited bio will chain to
its parent bio, the real parent's end_io won't be called until both parent bio
and bio have completed, so I think it's safe here. :)

> So far I've seen no error in any test cases.

I haven't seen any hungtask so far too.

Thanks,