| Message ID | 20190530004906.261170-2-drosen@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | F2FS Checkpointing without GC, related fixes | expand |
On 2019/5/30 8:49, Daniel Rosenberg wrote: > The existing threshold for allowable holes at checkpoint=disable time is > too high. The OVP space contains reserved segments, which are always in > the form of free segments. These must be subtracted from the OVP value. > > The current threshold is meant to be the maximum value of holes of a > single type we can have and still guarantee that we can fill the disk > without failing to find space for a block of a given type. > > If the disk is full, ignoring current reserved, which only helps us, > the amount of unused blocks is equal to the OVP area. Of that, there > are reserved segments, which must be free segments, and the rest of the > ovp area, which can come from either free segments or holes. The maximum > possible amount of holes is OVP-reserved. > > Now, consider the disk when mounting with checkpoint=disable. > We must be able to fill all available free space with either data or > node blocks. When we start with checkpoint=disable, holes are locked to > their current type. Say we have H of one type of hole, and H+X of the > other. We can fill H of that space with arbitrary typed blocks via SSR. > For the remaining H+X blocks, we may not have any of a given block type > left at all. For instance, if we were to fill the disk entirely with > blocks of the type with fewer holes, the H+X blocks of the opposite type > would not be used. If H+X > OVP-reserved, there would be more holes than > could possibly exist, and we would have failed to find a suitable block > earlier on, leading to a crash in update_sit_entry. > > If H+X <= OVP-reserved, then the holes end up effectively masked by the OVP > region in this case. > > Signed-off-by: Daniel Rosenberg <drosen@google.com> Reviewed-by: Chao Yu <yuchao0@huawei.com> Thanks,
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c index 1a83115284b93..ec59cbd0e661d 100644 --- a/fs/f2fs/segment.c +++ b/fs/f2fs/segment.c @@ -876,7 +876,9 @@ void f2fs_dirty_to_prefree(struct f2fs_sb_info *sbi) int f2fs_disable_cp_again(struct f2fs_sb_info *sbi) { struct dirty_seglist_info *dirty_i = DIRTY_I(sbi); - block_t ovp = overprovision_segments(sbi) << sbi->log_blocks_per_seg; + int ovp_hole_segs = + (overprovision_segments(sbi) - reserved_segments(sbi)); + block_t ovp_holes = ovp_hole_segs << sbi->log_blocks_per_seg; block_t holes[2] = {0, 0}; /* DATA and NODE */ struct seg_entry *se; unsigned int segno; @@ -891,10 +893,10 @@ int f2fs_disable_cp_again(struct f2fs_sb_info *sbi) } mutex_unlock(&dirty_i->seglist_lock); - if (holes[DATA] > ovp || holes[NODE] > ovp) + if (holes[DATA] > ovp_holes || holes[NODE] > ovp_holes) return -EAGAIN; if (is_sbi_flag_set(sbi, SBI_CP_DISABLED_QUICK) && - dirty_segments(sbi) > overprovision_segments(sbi)) + dirty_segments(sbi) > ovp_hole_segs) return -EAGAIN; return 0; }
The existing threshold for allowable holes at checkpoint=disable time is too high. The OVP space contains reserved segments, which are always in the form of free segments. These must be subtracted from the OVP value. The current threshold is meant to be the maximum value of holes of a single type we can have and still guarantee that we can fill the disk without failing to find space for a block of a given type. If the disk is full, ignoring current reserved, which only helps us, the amount of unused blocks is equal to the OVP area. Of that, there are reserved segments, which must be free segments, and the rest of the ovp area, which can come from either free segments or holes. The maximum possible amount of holes is OVP-reserved. Now, consider the disk when mounting with checkpoint=disable. We must be able to fill all available free space with either data or node blocks. When we start with checkpoint=disable, holes are locked to their current type. Say we have H of one type of hole, and H+X of the other. We can fill H of that space with arbitrary typed blocks via SSR. For the remaining H+X blocks, we may not have any of a given block type left at all. For instance, if we were to fill the disk entirely with blocks of the type with fewer holes, the H+X blocks of the opposite type would not be used. If H+X > OVP-reserved, there would be more holes than could possibly exist, and we would have failed to find a suitable block earlier on, leading to a crash in update_sit_entry. If H+X <= OVP-reserved, then the holes end up effectively masked by the OVP region in this case. Signed-off-by: Daniel Rosenberg <drosen@google.com> --- fs/f2fs/segment.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-)