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

[Chao Yu]

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.

Thanks,

>