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SubjectRe: [f2fs-dev] [PATCH 2/2] f2fs: avoid infinite GC loop due to stale atomic files
On 09/09, Chao Yu wrote:
> On 2019/9/9 16:21, Jaegeuk Kim wrote:
> > On 09/09, Chao Yu wrote:
> >> On 2019/9/9 16:01, Jaegeuk Kim wrote:
> >>> On 09/09, Chao Yu wrote:
> >>>> On 2019/9/9 15:30, Jaegeuk Kim wrote:
> >>>>> On 09/09, Chao Yu wrote:
> >>>>>> On 2019/9/9 9:25, Jaegeuk Kim wrote:
> >>>>>>> If committing atomic pages is failed when doing f2fs_do_sync_file(), we can
> >>>>>>> get commited pages but atomic_file being still set like:
> >>>>>>>
> >>>>>>> - inmem: 0, atomic IO: 4 (Max. 10), volatile IO: 0 (Max. 0)
> >>>>>>>
> >>>>>>> If GC selects this block, we can get an infinite loop like this:
> >>>>>>>
> >>>>>>> f2fs_submit_page_bio: dev = (253,7), ino = 2, page_index = 0x2359a8, oldaddr = 0x2359a8, newaddr = 0x2359a8, rw = READ(), type = COLD_DATA
> >>>>>>> f2fs_submit_read_bio: dev = (253,7)/(253,7), rw = READ(), DATA, sector = 18533696, size = 4096
> >>>>>>> f2fs_get_victim: dev = (253,7), type = No TYPE, policy = (Foreground GC, LFS-mode, Greedy), victim = 4355, cost = 1, ofs_unit = 1, pre_victim_secno = 4355, prefree = 0, free = 234
> >>>>>>> f2fs_iget: dev = (253,7), ino = 6247, pino = 5845, i_mode = 0x81b0, i_size = 319488, i_nlink = 1, i_blocks = 624, i_advise = 0x2c
> >>>>>>> f2fs_submit_page_bio: dev = (253,7), ino = 2, page_index = 0x2359a8, oldaddr = 0x2359a8, newaddr = 0x2359a8, rw = READ(), type = COLD_DATA
> >>>>>>> f2fs_submit_read_bio: dev = (253,7)/(253,7), rw = READ(), DATA, sector = 18533696, size = 4096
> >>>>>>> f2fs_get_victim: dev = (253,7), type = No TYPE, policy = (Foreground GC, LFS-mode, Greedy), victim = 4355, cost = 1, ofs_unit = 1, pre_victim_secno = 4355, prefree = 0, free = 234
> >>>>>>> f2fs_iget: dev = (253,7), ino = 6247, pino = 5845, i_mode = 0x81b0, i_size = 319488, i_nlink = 1, i_blocks = 624, i_advise = 0x2c
> >>>>>>>
> >>>>>>> In that moment, we can observe:
> >>>>>>>
> >>>>>>> [Before]
> >>>>>>> Try to move 5084219 blocks (BG: 384508)
> >>>>>>> - data blocks : 4962373 (274483)
> >>>>>>> - node blocks : 121846 (110025)
> >>>>>>> Skipped : atomic write 4534686 (10)
> >>>>>>>
> >>>>>>> [After]
> >>>>>>> Try to move 5088973 blocks (BG: 384508)
> >>>>>>> - data blocks : 4967127 (274483)
> >>>>>>> - node blocks : 121846 (110025)
> >>>>>>> Skipped : atomic write 4539440 (10)
> >>>>>>>
> >>>>>>> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
> >>>>>>> ---
> >>>>>>> fs/f2fs/file.c | 10 +++++-----
> >>>>>>> 1 file changed, 5 insertions(+), 5 deletions(-)
> >>>>>>>
> >>>>>>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> >>>>>>> index 7ae2f3bd8c2f..68b6da734e5f 100644
> >>>>>>> --- a/fs/f2fs/file.c
> >>>>>>> +++ b/fs/f2fs/file.c
> >>>>>>> @@ -1997,11 +1997,11 @@ static int f2fs_ioc_commit_atomic_write(struct file *filp)
> >>>>>>> goto err_out;
> >>>>>>>
> >>>>>>> ret = f2fs_do_sync_file(filp, 0, LLONG_MAX, 0, true);
> >>>>>>> - if (!ret) {
> >>>>>>> - clear_inode_flag(inode, FI_ATOMIC_FILE);
> >>>>>>> - F2FS_I(inode)->i_gc_failures[GC_FAILURE_ATOMIC] = 0;
> >>>>>>> - stat_dec_atomic_write(inode);
> >>>>>>> - }
> >>>>>>> +
> >>>>>>> + /* doesn't need to check error */
> >>>>>>> + clear_inode_flag(inode, FI_ATOMIC_FILE);
> >>>>>>> + F2FS_I(inode)->i_gc_failures[GC_FAILURE_ATOMIC] = 0;
> >>>>>>> + stat_dec_atomic_write(inode);
> >>>>>>
> >>>>>> If there are still valid atomic write pages linked in .inmem_pages, it may cause
> >>>>>> memory leak when we just clear FI_ATOMIC_FILE flag.
> >>>>>
> >>>>> f2fs_commit_inmem_pages() should have flushed them.
> >>>>
> >>>> Oh, we failed to flush its nodes.
> >>>>
> >>>> However we won't clear such info if we failed to flush inmen pages, it looks
> >>>> inconsistent.
> >>>>
> >>>> Any interface needed to drop inmem pages or clear ATOMIC_FILE flag in that two
> >>>> error path? I'm not very clear how sqlite handle such error.
> >>>
> >>> f2fs_drop_inmem_pages() did that, but not in this case.
> >>
> >> What I mean is, for any error returned from atomic_commit() interface, should
> >> userspace application handle it with consistent way, like trigger
> >> f2fs_drop_inmem_pages(), so we don't need to handle it inside atomic_commit().
> >
> > f2fs_ioc_abort_volatile_write() will be triggered.
>
> If userspace can do this, we can get rid of this patch, or am I missing sth?

We don't know when that will come. And, other threads are waiting for GC here.

>
> - f2fs_ioc_abort_volatile_write
> - f2fs_drop_inmem_pages
> - clear_inode_flag(inode, FI_ATOMIC_FILE);
> - fi->i_gc_failures[GC_FAILURE_ATOMIC] = 0;
> - stat_dec_atomic_write(inode);
>
> >
> >>
> >>>
> >>>>
> >>>> Thanks,
> >>>>
> >>>>>
> >>>>>>
> >>>>>> So my question is why below logic didn't handle such condition well?
> >>>>>>
> >>>>>> f2fs_gc()
> >>>>>>
> >>>>>> if (has_not_enough_free_secs(sbi, sec_freed, 0)) {
> >>>>>> if (skipped_round <= MAX_SKIP_GC_COUNT ||
> >>>>>> skipped_round * 2 < round) {
> >>>>>> segno = NULL_SEGNO;
> >>>>>> goto gc_more;
> >>>>>> }
> >>>>>>
> >>>>>> if (first_skipped < last_skipped &&
> >>>>>> (last_skipped - first_skipped) >
> >>>>>> sbi->skipped_gc_rwsem) {
> >>>>>> f2fs_drop_inmem_pages_all(sbi, true);
> >>>>>
> >>>>> This is doing nothing, since f2fs_commit_inmem_pages() removed the inode
> >>>>> from inmem list.
> >>>>>
> >>>>>> segno = NULL_SEGNO;
> >>>>>> goto gc_more;
> >>>>>> }
> >>>>>> if (gc_type == FG_GC && !is_sbi_flag_set(sbi, SBI_CP_DISABLED))
> >>>>>> ret = f2fs_write_checkpoint(sbi, &cpc);
> >>>>>> }
> >>>>>>
> >>>>>>> } else {
> >>>>>>> ret = f2fs_do_sync_file(filp, 0, LLONG_MAX, 1, false);
> >>>>>>> }
> >>>>>>>
> >>>>> .
> >>>>>
> >>> .
> >>>
> > .
> >

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