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SubjectRe: [f2fs-dev] [PATCH v3] f2fs: avoid fi->i_gc_rwsem[WRITE] lock in f2fs_gc
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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@kernel.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?

diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index 870b337e9f7f..40f103508432 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -1142,7 +1142,7 @@ 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 int skipped_round = 0, round = 0;
+ unsigned int skipped_round = 0, round = 0, atomic_skipped;

trace_f2fs_gc_begin(sbi->sb, sync, background,
get_pages(sbi, F2FS_DIRTY_NODES),
@@ -1196,8 +1196,9 @@ 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 ||
- sbi->skipped_gc_rwsem)
+ atomic_skipped =
+ sbi->skipped_atomic_files[FG_GC] - last_skipped;
+ if (atomic_skipped || sbi->skipped_gc_rwsem)
skipped_round++;
last_skipped = sbi->skipped_atomic_files[FG_GC];
round++;
@@ -1216,9 +1217,7 @@ 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] >
- sbi->skipped_gc_rwsem) {
+ if (atomic_skipped && atomic_skipped > sbi->skipped_gc_rwsem) {
f2fs_drop_inmem_pages_all(sbi, true);
segno = NULL_SEGNO;
goto gc_more;
Thanks,

> + }
> 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;
>

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