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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 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.

>
> 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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