On 01/04, Yunlong Song wrote:
> Hi Kim,
> Although the blocks of that file will finally be discarded when it is not current segment any more and almost fully invalidate,
> but the point is that the blocks of that file can only be discarded along with the whole segment now, which violates the meaning
> of small discard. Look at the case I said in last mail, if the segment which owns the deleted file has no more changing after the file
> deleting, and its validate blocks are perhaps over 95%, and it may not be easy to be selected as a gc victim. In this case, FTL can
> not know the "file delete" on time, and the invalidate blocks of that file can not be discarded in FTL layer on time.
Correction: current active segment is also treated as a candidate for small
discards in add_discard_addrs().
So, it seems you want to discard small invalid chunks in the current active
segments, right? If so, how do you think this change?
---
fs/f2fs/segment.c | 9 ++++-----
1 file changed, 4 insertions(+), 5 deletions(-)
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
index 82078734f379..394a6fef7f82 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -853,11 +853,10 @@ static bool add_discard_addrs(struct f2fs_sb_info *sbi, struct cp_control *cpc,
if (se->valid_blocks == max_blocks || !f2fs_discard_en(sbi))
return false;
- if (!force) {
- if (!test_opt(sbi, DISCARD) || !se->valid_blocks ||
- SM_I(sbi)->nr_discards >= SM_I(sbi)->max_discards)
- return false;
- }
+ if (!force && (!test_opt(sbi, DISCARD) ||
+ (!se->valid_blocks && !IS_CURSEG(sbi, cpc->trim_start)) ||
+ SM_I(sbi)->nr_discards >= SM_I(sbi)->max_discards))
+ return false;
/* SIT_VBLOCK_MAP_SIZE should be multiple of sizeof(unsigned long) */
for (i = 0; i < entries; i++)
--
2.11.0
>
> On 2017/1/4 9:55, Jaegeuk Kim wrote:
> > Hi Yunlong,
> >
> > On 01/03, Yunlong Song wrote:
> >> In the small discard case, when se->valid_blocks is zero, the add_discard_addrs
> >> will directly return without __add_discard_entry. This will cause the file
> >> delete have no small discard. The case is like this:
> >>
> >> 1. Allocate free 2M segment
> >> 2. Write a file (size n blocks < 512) in that 2M segment, se->valid_blocks = n
> >> 3. Delete that file, se->valid_blocks = 0, add_discard_addrs will return without
> >> sending any discard of that file, and forever due to cur_map[i] ^ ckpt_map[i] =
> >> 0 after that checkpoint
> > During this checkpoint, that'll be discarded as a prefree segment, no?
> > Note that, if this is a current segment, f2fs won't discard it until it is
> > fully allocated.
> >
> > Thanks,
> >
> >> Signed-off-by: Yunlong Song <yunlong.song@xxxxxxxxxx>
> >> ---
> >> fs/f2fs/segment.c | 2 +-
> >> 1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> >> index 0738f48..8610f14 100644
> >> --- a/fs/f2fs/segment.c
> >> +++ b/fs/f2fs/segment.c
> >> @@ -838,7 +838,7 @@ static void add_discard_addrs(struct f2fs_sb_info *sbi, struct cp_control *cpc)
> >> return;
> >>
> >> if (!force) {
> >> - if (!test_opt(sbi, DISCARD) || !se->valid_blocks ||
> >> + if (!test_opt(sbi, DISCARD) ||
> >> SM_I(sbi)->nr_discards >= SM_I(sbi)->max_discards)
> >> return;
> >> }
> >> --
> >> 1.8.5.2
> > .
> >
>
>
> --
> Thanks,
> Yunlong Song
>
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