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

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Date:   Fri, 10 Sep 2021 07:34:34 -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 Thu, Sep 9, 2021 at 4:50 PM Chao Yu <chao@...nel.org> wrote:
>
> On 2021/9/8 2:12, Daeho Jeong wrote:
> > 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?
>
> Daeho,
>
> I guess we can record left hole size in seg->fragment_remained_hole.
>

I understand we need a new fragment_remained_hole variable in segment structure.
But, I mean.. How can we pass over the left hole size from the
previous segment to the next segment?

Thanks,

> Thanks,
>
> >
> > Thanks,
> >
> >> Thanks,
> >>
> >>>