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

[Chao Yu]

On 2021/9/8 2:12, Daeho Jeong wrote:
> On Fri, Sep 3, 2021 at 11:45 PM Chao Yu <chao@xxxxxxxxxx> 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.

Thanks,

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