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Date: Sat, 28 Oct 2017 20:02:54 +0800 From: Chao Yu <chao@...nel.org> To: Yunlong Song <yunlong.song@...wei.com>, yunlong.song@...oud.com Cc: Chao Yu <yuchao0@...wei.com>, jaegeuk@...nel.org, linux-fsdevel@...r.kernel.org, miaoxie@...wei.com, linux-kernel@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net Subject: Re: [f2fs-dev] [PATCH v2] f2fs: update dirty status for CURSEG as well Hi Yunlong, I think you're so busy, I just help to refactor your patch, and send it out authored with you, please check that patch, if you have different opinion, let me know. Thanks, On 2017/10/16 11:43, Chao Yu wrote: > On 2017/10/14 20:53, Yunlong Song wrote: >> Oh, yes it is. I found that problem in a kernel tree which does not have >> commit >> c6f82fe90d7458e5fa190a6820bfc24f96b0de4e (Revert "f2fs: put allocate_segment >> after refresh_sit_entry"). In that kernel, the allocate_segment is still >> behind >> refresh_sit_entry. Now I understand the commit message: >> "This makes a leak to register dirty segments. I reproduced the issue by >> modified postmark which injects a lot of file create/delete/update and >> finally triggers huge number of SSR allocations." >> >> The reason is that if refresh_sit_entry is before allocate_segment, then the >> dirty status of CURSEG is not updated, as a result, the count of dirty >> segments >> is wrong, which is much smaller than its real value. Then the f2fs_gc >> can not >> do its work since it can not even get one victim, then the free segments are >> used up and then triggers much SSR. So Jay reverts the patch. >> >> It seems there are two options: >> (1) keep this patch ([PATCH v2] f2fs: update dirty status for CURSEG as >> well) >> and we can recover commit 3436c4bdb30de421d46f58c9174669fbcfd40ce0 >> (f2fs: put allocate_segment after refresh_sit_entry) >> (2) remove this patch at all >> >> It seems (1) is robust, but (2) avoids unnecessary check. > > What about reverting 5e443818fa0b ("f2fs: handle dirty segments inside > refresh_sit_entry") to keep the original order: > > 1. update sit info > 2. allocate new segment > 3. update dirty status of segment > > Thanks, > >> >> On 2017/10/14 8:14, Chao Yu wrote: >>> On 2017/10/13 21:21, Yunlong Song wrote: >>>> Without this patch, it will cause all the free segments using up in some >>>> corner case. For example, there are 100 segments, and 20 of them are >>>> reserved for ovp. If 79 segments are full of data, segment 80 becomes >>>> CURSEG segment, write 512 blocks and then delete 511 blocks. Since it is >>>> CURSEG segment, the __locate_dirty_segment will not update its dirty >>>> status. Then the dirty_segments(sbi) is 0, f2fs_gc will fail to >>>> get_victim, and f2fs_balance_fs will fail to trigger gc action. After >>>> f2fs_balance_fs returns, f2fs can continue to write data to segment 81. >>>> Again, segment 81 becomes CURSEG segment, write 512 blocks and delete >>>> 511 blocks, the dirty_segments(sbi) is 0 and f2fs_gc fail again. This >>>> can finally use up all the free segments and cause panic. >>> Look into this patch again, I found refresh_sit_entry is called after >>> ->allocate_segment, so if all 512 blocks were allocated, log header should >>> have been moved to another segment, so locate_dirty_segment in >>> refresh_sit_entry should update dirty status of previous segment correctly, >>> anything I'm missing? >>> >>> Thanks, >>> >>>> Signed-off-by: Yunlong Song <yunlong.song@...wei.com> >>>> --- >>>> fs/f2fs/segment.c | 4 ++-- >>>> 1 file changed, 2 insertions(+), 2 deletions(-) >>>> >>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c >>>> index bfbcff8..0fce076 100644 >>>> --- a/fs/f2fs/segment.c >>>> +++ b/fs/f2fs/segment.c >>>> @@ -687,7 +687,7 @@ static void __locate_dirty_segment(struct f2fs_sb_info *sbi, unsigned int segno, >>>> struct dirty_seglist_info *dirty_i = DIRTY_I(sbi); >>>> >>>> /* need not be added */ >>>> - if (IS_CURSEG(sbi, segno)) >>>> + if (IS_CURSEG(sbi, segno) && dirty_type == PRE) >>>> return; >>>> >>>> if (!test_and_set_bit(segno, dirty_i->dirty_segmap[dirty_type])) >>>> @@ -737,7 +737,7 @@ static void locate_dirty_segment(struct f2fs_sb_info *sbi, unsigned int segno) >>>> struct dirty_seglist_info *dirty_i = DIRTY_I(sbi); >>>> unsigned short valid_blocks; >>>> >>>> - if (segno == NULL_SEGNO || IS_CURSEG(sbi, segno)) >>>> + if (segno == NULL_SEGNO) >>>> return; >>>> >>>> mutex_lock(&dirty_i->seglist_lock); >>>> >>> . >>> >> >
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