Messages in this thread Patch in this message | | | Date | Tue, 28 Nov 2023 14:22:37 +0800 | Subject | Re: [PATCH 1/1] f2fs: fix fallocate failed under pinned block situation | From | Chao Yu <> |
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On 2023/11/17 7:34, Wu Bo wrote: > On 2023/11/11 12:49, Chao Yu wrote: >> On 2023/11/8 21:48, Wu Bo wrote: >>> On 2023/11/7 22:39, Chao Yu wrote: >>>> On 2023/10/30 17:40, Wu Bo wrote: >>>>> If GC victim has pinned block, it can't be recycled. >>>>> And if GC is foreground running, after many failure try, the pinned file >>>>> is expected to be clear pin flag. To enable the section be recycled. >>>>> >>>>> But when fallocate trigger FG_GC, GC can never recycle the pinned >>>>> section. Because GC will go to stop before the failure try meet the >>>>> threshold: >>>>> if (has_enough_free_secs(sbi, sec_freed, 0)) { >>>>> if (!gc_control->no_bg_gc && >>>>> total_sec_freed < gc_control->nr_free_secs) >>>>> goto go_gc_more; >>>>> goto stop; >>>>> } >>>>> >>>>> So when fallocate trigger FG_GC, at least recycle one. >>>> >>>> Hmm... it may break pinfile's semantics at least on one pinned file? >>>> In this case, I prefer to fail fallocate() rather than unpinning file, >>>> in order to avoid leaving invalid LBA references of unpinned file held >>>> by userspace. >>> >>> As f2fs designed now, FG_GC is able to unpin the pinned file. >>> >>> fallocate() triggered FG_GC, but can't recycle space. It breaks the >>> design logic of FG_GC. >> >> Yes, contradictoriness exists. >> >> IMO, unpin file by GC looks more dangerous, it may cause potential data >> corruption w/ below case: >> 1. app pins file & holds LBAs of data blocks. >> 2. GC unpins file and migrates its data to new LBAs. >> 3. other file reuses previous LBAs. >> 4. app read/write data via previous LBAs. >> >> So I suggest to normalize use of pinfile and do not add more unpin cases >> in filesystem inner processes. >> >>> >>> This issue is happened in Android OTA scenario. fallocate() always >>> return failure cause OTA fail. >> >> Can you please check why other pinned files were so fragmented that f2fs_gc() >> can not recycle one free section? >> > Not because pinned files were fragmented, but if the GC victim section has one block is pinned will cause this issue. > > If the section don't unpin the block, it can't be recycled. But there is high chance that the pinned section will be chosen next time under f2fs current victim selection strategy. > > So if we want to avoid unpin files, I think change victim selection to considering pinned blocks can fix this issue.
Oh, I get it.
How about this?
diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c index 325dab01a29d..3fb52dec5df8 100644 --- a/fs/f2fs/file.c +++ b/fs/f2fs/file.c @@ -1730,7 +1730,10 @@ next_alloc: f2fs_down_write(&sbi->gc_lock); stat_inc_gc_call_count(sbi, FOREGROUND); err = f2fs_gc(sbi, &gc_control); - if (err && err != -ENODATA) + + if (err == -EAGAIN) + f2fs_balance_fs(sbi, true); + else if (err && err != -ENODATA) goto out_err; }
However, the code won't fix contradictoriness issue, because the root cause is we left fragmented pinned data in filesystem, which should be avoided in GC-reliance LFS filesyetem as much as possible. Thanks,
> >> Thanks, >> >>> >>> And this commit changed previous behavior of fallocate(): >>> >>> Commit 2e42b7f817ac ("f2fs: stop allocating pinned sections if EAGAIN >>> happens") >>> >>> Before this commit, if fallocate() meet this situation, it will trigger >>> FG_GC to recycle pinned space finally. >>> >>> FG_GC is expected to recycle pinned space when there is no more free >>> space. And this is the right time to do it when fallocate() need free >>> space. >>> >>> It is weird when f2fs shows enough spare space but can't fallocate(). So >>> I think it should be fixed. >>> >>>> >>>> Thoughts? >>>> >>>> Thanks, >>>> >>>>> >>>>> This issue can be reproduced by filling f2fs space as following layout. >>>>> Every segment has one block is pinned: >>>>> +-+-+-+-+-+-+-----+-+ >>>>> | | |p| | | | ... | | seg_n >>>>> +-+-+-+-+-+-+-----+-+ >>>>> +-+-+-+-+-+-+-----+-+ >>>>> | | |p| | | | ... | | seg_n+1 >>>>> +-+-+-+-+-+-+-----+-+ >>>>> ... >>>>> +-+-+-+-+-+-+-----+-+ >>>>> | | |p| | | | ... | | seg_n+k >>>>> +-+-+-+-+-+-+-----+-+ >>>>> >>>>> And following are steps to reproduce this issue: >>>>> dd if=/dev/zero of=./f2fs_pin.img bs=2M count=1024 >>>>> mkfs.f2fs f2fs_pin.img >>>>> mkdir f2fs >>>>> mount f2fs_pin.img ./f2fs >>>>> cd f2fs >>>>> dd if=/dev/zero of=./large_padding bs=1M count=1760 >>>>> ./pin_filling.sh >>>>> rm padding* >>>>> sync >>>>> touch fallocate_40m >>>>> f2fs_io pinfile set fallocate_40m >>>>> fallocate -l 41943040 fallocate_40m >>>>> >>>>> fallocate always fail with EAGAIN even there has enough free space. >>>>> >>>>> 'pin_filling.sh' is: >>>>> count=1 >>>>> while : >>>>> do >>>>> # filling the seg space >>>>> for i in {1..511}: >>>>> do >>>>> name=padding_$count-$i >>>>> echo write $name >>>>> dd if=/dev/zero of=./$name bs=4K count=1 > /dev/null 2>&1 >>>>> if [ $? -ne 0 ]; then >>>>> exit 0 >>>>> fi >>>>> done >>>>> sync >>>>> >>>>> # pin one block in a segment >>>>> name=pin_file$count >>>>> dd if=/dev/zero of=./$name bs=4K count=1 > /dev/null 2>&1 >>>>> sync >>>>> f2fs_io pinfile set $name >>>>> count=$(($count + 1)) >>>>> done >>>>> >>>>> Signed-off-by: Wu Bo <bo.wu@vivo.com> >>>>> --- >>>>> fs/f2fs/file.c | 2 +- >>>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>>> >>>>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c >>>>> index ca5904129b16..e8a13616543f 100644 >>>>> --- a/fs/f2fs/file.c >>>>> +++ b/fs/f2fs/file.c >>>>> @@ -1690,7 +1690,7 @@ static int f2fs_expand_inode_data(struct inode >>>>> *inode, loff_t offset, >>>>> .init_gc_type = FG_GC, >>>>> .should_migrate_blocks = false, >>>>> .err_gc_skipped = true, >>>>> - .nr_free_secs = 0 }; >>>>> + .nr_free_secs = 1 }; >>>>> pgoff_t pg_start, pg_end; >>>>> loff_t new_size; >>>>> loff_t off_end;
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