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Date: Thu, 9 Aug 2018 12:59:17 -0700
From: Jaegeuk Kim <jaegeuk@...nel.org>
To: Chao Yu <yuchao0@...wei.com>
Cc: linux-kernel@...r.kernel.org,
linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH v3] f2fs: avoid fi->i_gc_rwsem[WRITE] lock in
f2fs_gc
On 08/09, Chao Yu wrote:
> On 2018/8/6 0:34, 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@...nel.org>
> > ---
> > v3
> > - don't revoke atomic_writes all the time due to gc_rwsem
> > - keep lock order in f2fs_commit_inmem_pages
> >
> > fs/f2fs/f2fs.h | 1 +
> > fs/f2fs/file.c | 76 ++++++++++++++++++++++++-----------------------
> > fs/f2fs/gc.c | 24 +++++++++++----
> > fs/f2fs/segment.c | 6 +++-
> > fs/f2fs/segment.h | 2 +-
> > 5 files changed, 64 insertions(+), 45 deletions(-)
> >
> > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> > index 1647a13be7f9..0c65c3146ead 100644
> > --- a/fs/f2fs/f2fs.h
> > +++ b/fs/f2fs/f2fs.h
> > @@ -1234,6 +1234,7 @@ 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 67c9c2d4e2d9..4e2e3938f474 100644
> > --- a/fs/f2fs/file.c
> > +++ b/fs/f2fs/file.c
> > @@ -1180,25 +1180,31 @@ 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);
> > - f2fs_lock_op(sbi);
> >
> > - f2fs_drop_extent_tree(inode);
> > + /* avoid gc operation during block exchange */
> > + down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> >
> > + f2fs_lock_op(sbi);
> > + f2fs_drop_extent_tree(inode);
> > + truncate_pagecache(inode, offset);
> > ret = __exchange_data_block(inode, inode, end, start, nrpages - end, true);
> > f2fs_unlock_op(sbi);
> > +
> > + up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> > 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;
> >
> > @@ -1213,21 +1219,13 @@ 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;
> >
> > @@ -1243,7 +1241,6 @@ 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;
> > }
> >
> > @@ -1418,9 +1415,6 @@ 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)
> > @@ -1431,13 +1425,15 @@ 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)
> > @@ -1451,6 +1447,7 @@ 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);
> > @@ -1460,7 +1457,6 @@ 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;
> > }
> >
> > @@ -1707,8 +1703,6 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
> >
> > inode_lock(inode);
> >
> > - down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> > -
> > if (f2fs_is_atomic_file(inode)) {
> > if (is_inode_flag_set(inode, FI_ATOMIC_REVOKE_REQUEST))
> > ret = -EINVAL;
> > @@ -1719,6 +1713,8 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
> > if (ret)
> > goto out;
> >
> > + down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> > +
> > if (!get_dirty_pages(inode))
> > goto skip_flush;
> >
> > @@ -1726,18 +1722,20 @@ static int f2fs_ioc_start_atomic_write(struct file *filp)
> > "Unexpected flush for atomic writes: ino=%lu, npages=%u",
> > inode->i_ino, get_dirty_pages(inode));
> > ret = filemap_write_and_wait_range(inode->i_mapping, 0, LLONG_MAX);
> > - if (ret)
> > + if (ret) {
> > + up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> > goto out;
> > + }
> > skip_flush:
> > set_inode_flag(inode, FI_ATOMIC_FILE);
> > clear_inode_flag(inode, FI_ATOMIC_REVOKE_REQUEST);
> > - f2fs_update_time(F2FS_I_SB(inode), REQ_TIME);
> > + up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
> >
> > + f2fs_update_time(F2FS_I_SB(inode), REQ_TIME);
> > F2FS_I(inode)->inmem_task = current;
> > 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;
> > @@ -1755,9 +1753,9 @@ 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;
> > @@ -1783,7 +1781,6 @@ 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;
> > @@ -2379,15 +2376,10 @@ 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 +2424,14 @@ static int f2fs_move_file_range(struct file *file_in, loff_t pos_in,
> > goto out_unlock;
> >
> > f2fs_balance_fs(sbi, true);
> > +
> > + 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;
> > + }
> > +
> > f2fs_lock_op(sbi);
> > ret = __exchange_data_block(src, dst, pos_in >> F2FS_BLKSIZE_BITS,
> > pos_out >> F2FS_BLKSIZE_BITS,
> > @@ -2444,13 +2444,15 @@ static int f2fs_move_file_range(struct file *file_in, loff_t pos_in,
> > f2fs_i_size_write(dst, dst_osize);
> > }
> > f2fs_unlock_op(sbi);
> > -out_unlock:
> > - if (src != dst) {
> > +
> > + if (src != dst)
> > up_write(&F2FS_I(dst)->i_gc_rwsem[WRITE]);
> > +out_src:
> > + up_write(&F2FS_I(src)->i_gc_rwsem[WRITE]);
> > +out_unlock:
> > + 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..d816c328f02b 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 +1116,23 @@ 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 &&
>
> For fggc, sbi->skipped_atomic_files[FG_GC] should always be last_skipped, since
> we assigned above.
>
> > + sbi->skipped_atomic_files[FG_GC] >
> > + sbi->skipped_gc_rwsem) {
> > + f2fs_drop_inmem_pages_all(sbi, true);
> > + segno = NULL_SEGNO;
> > + goto gc_more;
>
> I guess what you mean is:
>
> atomic_skipped = sbi->skipped_atomic_files[FG_GC] - last_skipped;
>
> if (atomic_skipped && atomic_skipped > sbi->skipped_gc_rwsem)
> f2fs_drop_inmem_pages_all();
>
> Is that right?
Yup, how about this?
diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index d816c328f02b..cb510fb36523 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -1052,6 +1052,7 @@ int f2fs_gc(struct f2fs_sb_info *sbi, bool sync,
.iroot = RADIX_TREE_INIT(gc_list.iroot, GFP_NOFS),
};
unsigned long long last_skipped = sbi->skipped_atomic_files[FG_GC];
+ unsigned long long first_skipped;
unsigned int skipped_round = 0, round = 0;
trace_f2fs_gc_begin(sbi->sb, sync, background,
@@ -1064,8 +1065,10 @@ 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:
+ sbi->skipped_gc_rwsem = 0;
+ first_skipped = last_skipped;
+
if (unlikely(!(sbi->sb->s_flags & SB_ACTIVE))) {
ret = -EINVAL;
goto stop;
@@ -1126,8 +1129,8 @@ int f2fs_gc(struct f2fs_sb_info *sbi, bool sync,
goto gc_more;
}
- if (sbi->skipped_atomic_files[FG_GC] == last_skipped &&
- sbi->skipped_atomic_files[FG_GC] >
+ if (first_skipped < last_skipped &&
+ (last_skipped - first_skipped) >
sbi->skipped_gc_rwsem) {
f2fs_drop_inmem_pages_all(sbi, true);
segno = NULL_SEGNO;
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