Message-ID: <20180805163450.GB55836@jaegeuk-macbookpro.roam.corp.google.com>
Date:   Sun, 5 Aug 2018 09:34:50 -0700
From:   Jaegeuk Kim <jaegeuk@...nel.org>
To:     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

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 &&
+				sbi->skipped_atomic_files[FG_GC] >
+						sbi->skipped_gc_rwsem) {
+			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..f4ac006dac43 100644
--- a/fs/f2fs/segment.c
+++ b/fs/f2fs/segment.c
@@ -445,8 +445,10 @@ int f2fs_commit_inmem_pages(struct inode *inode)
 	int err;
 
 	f2fs_balance_fs(sbi, true);
-	f2fs_lock_op(sbi);
 
+	down_write(&fi->i_gc_rwsem[WRITE]);
+
+	f2fs_lock_op(sbi);
 	set_inode_flag(inode, FI_ATOMIC_COMMIT);
 
 	mutex_lock(&fi->inmem_lock);
@@ -461,6 +463,8 @@ int f2fs_commit_inmem_pages(struct inode *inode)
 	clear_inode_flag(inode, FI_ATOMIC_COMMIT);
 
 	f2fs_unlock_op(sbi);
+	up_write(&fi->i_gc_rwsem[WRITE]);
+
 	return err;
 }
 
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;
-- 
2.17.0.441.gb46fe60e1d-goog

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