Re: [PATCH] f2fs: avoid fi->i_gc_rwsem[WRITE] lock in f2fs_gc

From: Jaegeuk Kim
Date: Mon Jul 30 2018 - 05:08:54 EST

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In reply to: Chao Yu: "Re: [PATCH] f2fs: avoid fi->i_gc_rwsem[WRITE] lock in f2fs_gc"
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On 07/30, Chao Yu wrote:
> On 2018/7/30 12:18, Jaegeuk Kim wrote:
> > On 07/30, Chao Yu wrote:
> >> On 2018/7/30 9:32, Jaegeuk Kim wrote:
> >>> The f2fs_gc() called by f2fs_balance_fs() requires to be called outside of
> >>> fi->i_gc_rwsem[WRITE], since f2fs_gc() can try to grab it in a loop.
> >>>
> >>> If it hits the miximum retrials in GC, let's give a chance to release
> >>> gc_mutex for a short time in order not to go into live lock in the worst
> >>> case.
> >>>
> >>> Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
> >>> ---
> >>> fs/f2fs/f2fs.h | 1 +
> >>> fs/f2fs/file.c | 62 ++++++++++++++++++++++-------------------------
> >>> fs/f2fs/gc.c | 22 ++++++++++++-----
> >>> fs/f2fs/segment.c | 5 +++-
> >>> fs/f2fs/segment.h | 2 +-
> >>> 5 files changed, 51 insertions(+), 41 deletions(-)
> >>>
> >>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> >>> index a9447c7d6570..50349780001b 100644
> >>> --- a/fs/f2fs/f2fs.h
> >>> +++ b/fs/f2fs/f2fs.h
> >>> @@ -1223,6 +1223,7 @@ struct f2fs_sb_info {
> >>> unsigned int gc_mode; /* current GC state */
> >>> /* for skip statistic */
> >>> unsigned long long skipped_atomic_files[2]; /* FG_GC and BG_GC */
> >>> + unsigned long long skipped_gc_rwsem; /* FG_GC only */
> >>>
> >>> /* threshold for gc trials on pinned files */
> >>> u64 gc_pin_file_threshold;
> >>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
> >>> index 78c1bd6b8497..2b7d26ebb294 100644
> >>> --- a/fs/f2fs/file.c
> >>> +++ b/fs/f2fs/file.c
> >>> @@ -1179,10 +1179,12 @@ static int __exchange_data_block(struct inode *src_inode,
> >>> return ret;
> >>> }
> >>>
> >>> -static int f2fs_do_collapse(struct inode *inode, pgoff_t start, pgoff_t end)
> >>> +static int f2fs_do_collapse(struct inode *inode, loff_t offset, loff_t len)
> >>> {
> >>> struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
> >>> pgoff_t nrpages = (i_size_read(inode) + PAGE_SIZE - 1) / PAGE_SIZE;
> >>> + pgoff_t start = offset >> PAGE_SHIFT;
> >>> + pgoff_t end = (offset + len) >> PAGE_SHIFT;
> >>> int ret;
> >>>
> >>> f2fs_balance_fs(sbi, true);
> >>> @@ -1190,14 +1192,18 @@ static int f2fs_do_collapse(struct inode *inode, pgoff_t start, pgoff_t end)
> >>>
> >>> f2fs_drop_extent_tree(inode);
> >>>
> >>> + /* avoid gc operation during block exchange */
> >>> + down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> >>> + truncate_pagecache(inode, offset);
> >>> ret = __exchange_data_block(inode, inode, end, start, nrpages - end, true);
> >>> + up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> >>> +
> >>> f2fs_unlock_op(sbi);
> >>> return ret;
> >>> }
> >>>
> >>> static int f2fs_collapse_range(struct inode *inode, loff_t offset, loff_t len)
> >>> {
> >>> - pgoff_t pg_start, pg_end;
> >>> loff_t new_size;
> >>> int ret;
> >>>
> >>> @@ -1212,21 +1218,13 @@ static int f2fs_collapse_range(struct inode *inode, loff_t offset, loff_t len)
> >>> if (ret)
> >>> return ret;
> >>>
> >>> - pg_start = offset >> PAGE_SHIFT;
> >>> - pg_end = (offset + len) >> PAGE_SHIFT;
> >>> -
> >>> - /* avoid gc operation during block exchange */
> >>> - down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> >>> -
> >>> down_write(&F2FS_I(inode)->i_mmap_sem);
> >>> /* write out all dirty pages from offset */
> >>> ret = filemap_write_and_wait_range(inode->i_mapping, offset, LLONG_MAX);
> >>> if (ret)
> >>> goto out_unlock;
> >>>
> >>> - truncate_pagecache(inode, offset);
> >>> -
> >>> - ret = f2fs_do_collapse(inode, pg_start, pg_end);
> >>> + ret = f2fs_do_collapse(inode, offset, len);
> >>> if (ret)
> >>> goto out_unlock;
> >>>
> >>> @@ -1242,7 +1240,6 @@ static int f2fs_collapse_range(struct inode *inode, loff_t offset, loff_t len)
> >>> f2fs_i_size_write(inode, new_size);
> >>> out_unlock:
> >>> up_write(&F2FS_I(inode)->i_mmap_sem);
> >>> - up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> >>> return ret;
> >>> }
> >>>
> >>> @@ -1417,9 +1414,6 @@ static int f2fs_insert_range(struct inode *inode, loff_t offset, loff_t len)
> >>>
> >>> f2fs_balance_fs(sbi, true);
> >>>
> >>> - /* avoid gc operation during block exchange */
> >>> - down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> >>> -
> >>> down_write(&F2FS_I(inode)->i_mmap_sem);
> >>> ret = f2fs_truncate_blocks(inode, i_size_read(inode), true);
> >>> if (ret)
> >>> @@ -1430,13 +1424,15 @@ static int f2fs_insert_range(struct inode *inode, loff_t offset, loff_t len)
> >>> if (ret)
> >>> goto out;
> >>>
> >>> - truncate_pagecache(inode, offset);
> >>> -
> >>> pg_start = offset >> PAGE_SHIFT;
> >>> pg_end = (offset + len) >> PAGE_SHIFT;
> >>> delta = pg_end - pg_start;
> >>> idx = (i_size_read(inode) + PAGE_SIZE - 1) / PAGE_SIZE;
> >>>
> >>> + /* avoid gc operation during block exchange */
> >>> + down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> >>> + truncate_pagecache(inode, offset);
> >>> +
> >>> while (!ret && idx > pg_start) {
> >>> nr = idx - pg_start;
> >>> if (nr > delta)
> >>> @@ -1450,6 +1446,7 @@ static int f2fs_insert_range(struct inode *inode, loff_t offset, loff_t len)
> >>> idx + delta, nr, false);
> >>> f2fs_unlock_op(sbi);
> >>> }
> >>> + up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> >>>
> >>> /* write out all moved pages, if possible */
> >>> filemap_write_and_wait_range(inode->i_mapping, offset, LLONG_MAX);
> >>> @@ -1459,7 +1456,6 @@ static int f2fs_insert_range(struct inode *inode, loff_t offset, loff_t len)
> >>> f2fs_i_size_write(inode, new_size);
> >>> out:
> >>> up_write(&F2FS_I(inode)->i_mmap_sem);
> >>> - up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> >>> return ret;
> >>> }
> >>>
> >>> @@ -1706,8 +1702,6 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
> >>>
> >>> inode_lock(inode);
> >>>
> >>> - down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> >>
> >> After removing lock here, how can we handle below condition:
> >>
> >> commit 27319ba4044c0c67d62ae39e53c0118c89f0a029
> >> Author: Chao Yu <yuchao0@xxxxxxxxxx>
> >> Date: Tue Apr 17 17:51:28 2018 +0800
> >>
> >> f2fs: fix race in between GC and atomic open
> >>
> >> Thread GC thread
> >> - f2fs_ioc_start_atomic_write
> >> - get_dirty_pages
> >> - filemap_write_and_wait_range
> >> - f2fs_gc
> >> - do_garbage_collect
> >> - gc_data_segment
> >> - move_data_page
> >> - f2fs_is_atomic_file
> >> - set_page_dirty
> >> - set_inode_flag(, FI_ATOMIC_FILE)
> >>
> >> Dirty data page can still be generated by GC in race condition as
> >> above call stack.
> >>
> >> This patch adds fi->dio_rwsem[WRITE] in f2fs_ioc_start_atomic_write
> >> to avoid such race.
> >
> > "f2fs: don't allow any writes on aborted atomic writes" disallows any writes
> > on atomic file which has the revoking flag. So, this won't happen. In GC,
>
> Hmmm... In above condition, it's not related to FI_ATOMIC_REVOKE_REQUEST flag
> since we do not drop any inmem pages for atomic file.
>
> That patch was trying to eliminate a hole which exists in between
> filemap_write_and_wait_range and set_inode_flag(, FI_ATOMIC_FILE), where GC can
> still dirty page in the inode, it can pollute isolation of database transaction,
> so that is why we need this lock.

Ah, GC can generate any dirty pages of atomic_written data before starting
another transaction, right?

I think we can do
- set_inode_flag() first, followed by
- filemap_write_and_wait_range().

Thoughts?

>
> Thanks,
>
> > f2fs_is_atomic_file won't make the page dirty. WDYT?
> >
> > Thanks,
> >
> >
> >>
> >> Thanks,
> >>
> >>> -
> >>> if (f2fs_is_atomic_file(inode)) {
> >>> if (is_inode_flag_set(inode, FI_ATOMIC_REVOKE_REQUEST))
> >>> ret = -EINVAL;
> >>> @@ -1736,7 +1730,6 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
> >>> stat_inc_atomic_write(inode);
> >>> stat_update_max_atomic_write(inode);
> >>> out:
> >>> - up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> >>> inode_unlock(inode);
> >>> mnt_drop_write_file(filp);
> >>> return ret;
> >>> @@ -1754,9 +1747,9 @@ static int f2fs_ioc_commit_atomic_write(struct file *filp)
> >>> if (ret)
> >>> return ret;
> >>>
> >>> - inode_lock(inode);
> >>> + f2fs_balance_fs(F2FS_I_SB(inode), true);
> >>>
> >>> - down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> >>> + inode_lock(inode);
> >>>
> >>> if (f2fs_is_volatile_file(inode)) {
> >>> ret = -EINVAL;
> >>> @@ -1782,7 +1775,6 @@ static int f2fs_ioc_commit_atomic_write(struct file *filp)
> >>> clear_inode_flag(inode, FI_ATOMIC_REVOKE_REQUEST);
> >>> ret = -EINVAL;
> >>> }
> >>> - up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> >>> inode_unlock(inode);
> >>> mnt_drop_write_file(filp);
> >>> return ret;
> >>> @@ -2378,15 +2370,10 @@ static int f2fs_move_file_range(struct file *file_in, loff_t pos_in,
> >>> }
> >>>
> >>> inode_lock(src);
> >>> - down_write(&F2FS_I(src)->i_gc_rwsem[WRITE]);
> >>> if (src != dst) {
> >>> ret = -EBUSY;
> >>> if (!inode_trylock(dst))
> >>> goto out;
> >>> - if (!down_write_trylock(&F2FS_I(dst)->i_gc_rwsem[WRITE])) {
> >>> - inode_unlock(dst);
> >>> - goto out;
> >>> - }
> >>> }
> >>>
> >>> ret = -EINVAL;
> >>> @@ -2432,6 +2419,14 @@ static int f2fs_move_file_range(struct file *file_in, loff_t pos_in,
> >>>
> >>> f2fs_balance_fs(sbi, true);
> >>> f2fs_lock_op(sbi);
> >>> +
> >>> + down_write(&F2FS_I(src)->i_gc_rwsem[WRITE]);
> >>> + if (src != dst) {
> >>> + ret = -EBUSY;
> >>> + if (!down_write_trylock(&F2FS_I(dst)->i_gc_rwsem[WRITE]))
> >>> + goto out_src;
> >>> + }
> >>> +
> >>> ret = __exchange_data_block(src, dst, pos_in >> F2FS_BLKSIZE_BITS,
> >>> pos_out >> F2FS_BLKSIZE_BITS,
> >>> len >> F2FS_BLKSIZE_BITS, false);
> >>> @@ -2442,14 +2437,15 @@ static int f2fs_move_file_range(struct file *file_in, loff_t pos_in,
> >>> else if (dst_osize != dst->i_size)
> >>> f2fs_i_size_write(dst, dst_osize);
> >>> }
> >>> + if (src != dst)
> >>> + up_write(&F2FS_I(dst)->i_gc_rwsem[WRITE]);
> >>> +out_src:
> >>> + up_write(&F2FS_I(src)->i_gc_rwsem[WRITE]);
> >>> f2fs_unlock_op(sbi);
> >>> out_unlock:
> >>> - if (src != dst) {
> >>> - up_write(&F2FS_I(dst)->i_gc_rwsem[WRITE]);
> >>> + if (src != dst)
> >>> inode_unlock(dst);
> >>> - }
> >>> out:
> >>> - up_write(&F2FS_I(src)->i_gc_rwsem[WRITE]);
> >>> inode_unlock(src);
> >>> return ret;
> >>> }
> >>> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> >>> index e352fbd33848..cac317e37306 100644
> >>> --- a/fs/f2fs/gc.c
> >>> +++ b/fs/f2fs/gc.c
> >>> @@ -884,6 +884,7 @@ static void gc_data_segment(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
> >>> if (!down_write_trylock(
> >>> &F2FS_I(inode)->i_gc_rwsem[WRITE])) {
> >>> iput(inode);
> >>> + sbi->skipped_gc_rwsem++;
> >>> continue;
> >>> }
> >>>
> >>> @@ -913,6 +914,7 @@ static void gc_data_segment(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
> >>> continue;
> >>> if (!down_write_trylock(
> >>> &fi->i_gc_rwsem[WRITE])) {
> >>> + sbi->skipped_gc_rwsem++;
> >>> up_write(&fi->i_gc_rwsem[READ]);
> >>> continue;
> >>> }
> >>> @@ -1062,6 +1064,7 @@ int f2fs_gc(struct f2fs_sb_info *sbi, bool sync,
> >>> prefree_segments(sbi));
> >>>
> >>> cpc.reason = __get_cp_reason(sbi);
> >>> + sbi->skipped_gc_rwsem = 0;
> >>> gc_more:
> >>> if (unlikely(!(sbi->sb->s_flags & SB_ACTIVE))) {
> >>> ret = -EINVAL;
> >>> @@ -1103,7 +1106,8 @@ int f2fs_gc(struct f2fs_sb_info *sbi, bool sync,
> >>> total_freed += seg_freed;
> >>>
> >>> if (gc_type == FG_GC) {
> >>> - if (sbi->skipped_atomic_files[FG_GC] > last_skipped)
> >>> + if (sbi->skipped_atomic_files[FG_GC] > last_skipped ||
> >>> + sbi->skipped_gc_rwsem)
> >>> skipped_round++;
> >>> last_skipped = sbi->skipped_atomic_files[FG_GC];
> >>> round++;
> >>> @@ -1112,15 +1116,21 @@ int f2fs_gc(struct f2fs_sb_info *sbi, bool sync,
> >>> if (gc_type == FG_GC)
> >>> sbi->cur_victim_sec = NULL_SEGNO;
> >>>
> >>> - if (!sync) {
> >>> - if (has_not_enough_free_secs(sbi, sec_freed, 0)) {
> >>> - if (skipped_round > MAX_SKIP_ATOMIC_COUNT &&
> >>> - skipped_round * 2 >= round)
> >>> - f2fs_drop_inmem_pages_all(sbi, true);
> >>> + if (sync)
> >>> + goto stop;
> >>> +
> >>> + 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 (sbi->skipped_atomic_files[FG_GC] == last_skipped) {
> >>> + f2fs_drop_inmem_pages_all(sbi, true);
> >>> + segno = NULL_SEGNO;
> >>> + goto gc_more;
> >>> + }
> >>> if (gc_type == FG_GC)
> >>> ret = f2fs_write_checkpoint(sbi, &cpc);
> >>> }
> >>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> >>> index 3662e1f429b4..15b3b095fd58 100644
> >>> --- a/fs/f2fs/segment.c
> >>> +++ b/fs/f2fs/segment.c
> >>> @@ -444,10 +444,12 @@ int f2fs_commit_inmem_pages(struct inode *inode)
> >>> struct f2fs_inode_info *fi = F2FS_I(inode);
> >>> int err;
> >>>
> >>> - f2fs_balance_fs(sbi, true);
> >>> + f2fs_balance_fs(F2FS_I_SB(inode), true);
> >>> +
> >>> f2fs_lock_op(sbi);
> >>>
> >>> set_inode_flag(inode, FI_ATOMIC_COMMIT);
> >>> + down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> >>>
> >>> mutex_lock(&fi->inmem_lock);
> >>> err = __f2fs_commit_inmem_pages(inode);
> >>> @@ -458,6 +460,7 @@ int f2fs_commit_inmem_pages(struct inode *inode)
> >>> spin_unlock(&sbi->inode_lock[ATOMIC_FILE]);
> >>> mutex_unlock(&fi->inmem_lock);
> >>>
> >>> + up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> >>> clear_inode_flag(inode, FI_ATOMIC_COMMIT);
> >>>
> >>> f2fs_unlock_op(sbi);
> >>> diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
> >>> index 50495515f0a0..b3d9e317ff0c 100644
> >>> --- a/fs/f2fs/segment.h
> >>> +++ b/fs/f2fs/segment.h
> >>> @@ -215,7 +215,7 @@ struct segment_allocation {
> >>> #define IS_DUMMY_WRITTEN_PAGE(page) \
> >>> (page_private(page) == (unsigned long)DUMMY_WRITTEN_PAGE)
> >>>
> >>> -#define MAX_SKIP_ATOMIC_COUNT 16
> >>> +#define MAX_SKIP_GC_COUNT 16
> >>>
> >>> struct inmem_pages {
> >>> struct list_head list;
> >>>
> >
> > .
> >

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In reply to: Chao Yu: "Re: [PATCH] f2fs: avoid fi->i_gc_rwsem[WRITE] lock in f2fs_gc"
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