On 2021/9/4 4:33, Daeho Jeong wrote:
if (f2fs_need_seq_seg(sbi))
return 0;
static inline bool f2fs_need_seq_seg(struct f2fs_sb_info *sbi)
{
return F2FS_OPTION(sbi).fs_mode == FS_MODE_FRAGMENT_FIXED_BLK;
}
Do you need this in select_policy(), either?
IMO, for this mode, I prefer to disable background GC and just use newly
written userdata to fragment image, so I think it's fine to keep it as it is
here.
Like,
if (f2fs_need_rand_seg(sbi))
p->offset = prandom_u32() % (MAIN_SECS(sbi) *
sbi->segs_per_sec);
else if (f2fs_need_seq_seg(sbi))
p->offset = 0;
One more concern... we'd better to save fragment_remained_hole as well
as fragment_remained_chunk, otherwise, if fragment_chunk_size +
fragment_hole_size > 512, fragment hole will be truncated to 512 -
fragment_chunk_size due to we won't create hole with enough size as
seg->next_blkoff has crossed end of current segment.
Sorry, I don't get it. You mean making fragment_remained_hole as a
global variable?
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.
Thanks,
Thanks,
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