linux-kernel - Re: [f2fs-dev] [PATCH v2] f2fs: introduce fragment allocation mode mount option

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Message-ID: <CACOAw_yhgo1_wrejKskSm=Rsw27ogx=TS_A=z=-NGLcecA-gYA@mail.gmail.com>
Date:   Fri, 27 Aug 2021 08:22:25 -0700
From:   Daeho Jeong <daeho43@...il.com>
To:     Chao Yu <chao@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net, kernel-team@...roid.com,
        Daeho Jeong <daehojeong@...gle.com>
Subject: Re: [f2fs-dev] [PATCH v2] f2fs: introduce fragment allocation mode
 mount option

> I'd like to add a fixed chunk/hole fragmentation mode in addition, then
> userspace can control the fragmented chunk/hole with fixed size.
>
> How do you think of renaming "fragment:block" to "fragment:rand_block", and
> then I can add "fragment:fixed_block" option and its logic in addition?
>

The reason I added the randomness on these values is the segment
selection in SSR mode.
If all the segments have the same free block counts, f2fs will
allocate a new segment sequentially in SSR.
This was what I didn't want. Plus, in the real world, the size of hole
and chunk will be different in different segments.

But, if you think we need this "fragment:fixed_block" mode, I am happy
to have it. :)

> Do we need to consider multiple thread scenario? in such case,
> .fragment_remained_chunk may update randomly.
>
> In addition, multiple log headers share one .fragment_remained_chunk,
> it may cause unexpected result, it means there may be continuous holes
> or chunks in locality due to swithing between different log headers.
>
> Thanks,
>

Oh, I overlooked that point. I am going to add the variable for each
segment as you said before.

Thanks,