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

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Date:   Tue, 7 Sep 2021 11:12:21 -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

On Fri, Sep 3, 2021 at 11:45 PM Chao Yu <chao@...nel.org> wrote:
>
> On 2021/9/4 12:40, Daeho Jeong wrote:
> >> 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.
>
> Oh, correct.
>
> > 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?
>
> Yes, the left 256 block-sized hole should be created before next chunk
> in next opened segment.
>

Chao,

Do you have any decent idea to pass the left hole size to the next
segment which will be allocated?

Thanks,

> Thanks,
>
> >