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SubjectRe: [PATCH v2] 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@kernel.org>
---
v2 log from v1:
- keep lock order: i_gc_rwsem -> lock_op

fs/f2fs/f2fs.h | 1 +
fs/f2fs/file.c | 76 ++++++++++++++++++++++++-----------------------
fs/f2fs/gc.c | 22 ++++++++++----
fs/f2fs/segment.c | 5 +++-
fs/f2fs/segment.h | 2 +-
5 files changed, 61 insertions(+), 45 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..7bcf47f41ef1 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -1179,25 +1179,31 @@ 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;

@@ -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]);
-
if (f2fs_is_atomic_file(inode)) {
if (is_inode_flag_set(inode, FI_ATOMIC_REVOKE_REQUEST))
ret = -EINVAL;
@@ -1718,6 +1712,8 @@ 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;

@@ -1725,18 +1721,20 @@ 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;
@@ -1754,9 +1752,9 @@ 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 +1780,6 @@ 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 +2375,10 @@ 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;
@@ -2431,6 +2423,14 @@ 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,
@@ -2443,13 +2443,15 @@ 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..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;
--
2.17.0.441.gb46fe60e1d-goog
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