linux-kernel - Re: [f2fs-dev] [PATCH v4] f2fs: introduce fragment allocation mode mount option

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Date:   Fri, 3 Sep 2021 21:40:13 -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 v4] f2fs: introduce fragment allocation mode
 mount option

> As a per curseg field.
>
> > Maybe, we run into the same race condition issue you told before for
> > fragment_remained_chunk.
> > Could you clarify this more?
>
> e.g.
>
> F2FS_OPTION(sbi).fs_mode = FS_MODE_FRAGMENT_FIXED_BLK
> fragment_chunk_size = 384
> fragment_hole_size = 384
>
> When creating hole:
>
> - f2fs_allocate_data_block
>   - __refresh_next_blkoff
>     chunk locates in [0, 383] of current segment
>     seg->next_blkoff = 384
>     sbi->fragment_remained_chunk = 0
>     then we will reset sbi->fragment_remained_chunk to 384
>     and move seg->next_blkoff forward to 768 (384 + 384)
>   - __has_curseg_space() returns false
>   - allocate_segment() allocates new current segment
>
> So, for such case that hole may cross two segments, hole size may be truncated
> to left size of previous segment.

First, sbi->fragment_remained_chunk should be seg->fragment_remained_chunk.
I understand what you mean, so you mean we need to take the leftover
"hole" size over to the next segment?
In the example, the leftover hole size will be (384 - (512-384)). Do
you want to take this over to the next segment?