Messages in this thread | | | Subject | Re: [f2fs-dev] [PATCH v4] f2fs: introduce fragment allocation mode mount option | From | Chao Yu <> | Date | Sat, 4 Sep 2021 11:33:20 +0800 |
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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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