Re: [f2fs-dev] [PATCH] f2fs: use rwlock instead of rwsem for journal

Chao Yu
2021-07-22T13:42:47Z

On 2021/7/22 9:41, Jaegeuk Kim wrote:
> This tries to fix priority inversion in the below condition resulting in
> long checkpoint delay.
>
> f2fs_get_node_info()
> - nat_tree_lock
> -> sleep in journal_rwsem
> checkpoint
> - waiting for nat_tree_lock
>
> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
> ---
> fs/f2fs/node.c | 16 ++++++++--------
> fs/f2fs/segment.c | 22 +++++++++++-----------
> fs/f2fs/segment.h | 2 +-
> 3 files changed, 20 insertions(+), 20 deletions(-)
>
> diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
> index 0be9e2d7120e..821a40e02fb4 100644
> --- a/fs/f2fs/node.c
> +++ b/fs/f2fs/node.c
> @@ -567,13 +567,13 @@ int f2fs_get_node_info(struct f2fs_sb_info *sbi, nid_t nid,
> memset(&ne, 0, sizeof(struct f2fs_nat_entry));
>
> /* Check current segment summary */
> - down_read(&curseg->journal_rwsem);
> + read_lock(&curseg->journal_rwlock);

It seem journal_rwsem covers too many operations, e.g.

- scan_curseg_cache
- add_free_nid
- f2fs_kmem_cache_alloc
- kmem_cache_alloc(__GFP_NOFAIL)

Thanks,

> i = f2fs_lookup_journal_in_cursum(journal, NAT_JOURNAL, nid, 0);
> if (i >= 0) {
> ne = nat_in_journal(journal, i);
> node_info_from_raw_nat(ni, &ne);
> }
> - up_read(&curseg->journal_rwsem);
> + read_unlock(&curseg->journal_rwlock);
> if (i >= 0) {
> up_read(&nm_i->nat_tree_lock);
> goto cache;
> @@ -2338,7 +2338,7 @@ static void scan_curseg_cache(struct f2fs_sb_info *sbi)
> struct f2fs_journal *journal = curseg->journal;
> int i;
>
> - down_read(&curseg->journal_rwsem);
> + read_lock(&curseg->journal_rwlock);
> for (i = 0; i < nats_in_cursum(journal); i++) {
> block_t addr;
> nid_t nid;
> @@ -2350,7 +2350,7 @@ static void scan_curseg_cache(struct f2fs_sb_info *sbi)
> else
> remove_free_nid(sbi, nid);
> }
> - up_read(&curseg->journal_rwsem);
> + read_unlock(&curseg->journal_rwlock);
> }
>
> static void scan_free_nid_bits(struct f2fs_sb_info *sbi)
> @@ -2799,7 +2799,7 @@ static void remove_nats_in_journal(struct f2fs_sb_info *sbi)
> struct f2fs_journal *journal = curseg->journal;
> int i;
>
> - down_write(&curseg->journal_rwsem);
> + write_lock(&curseg->journal_rwlock);
> for (i = 0; i < nats_in_cursum(journal); i++) {
> struct nat_entry *ne;
> struct f2fs_nat_entry raw_ne;
> @@ -2831,7 +2831,7 @@ static void remove_nats_in_journal(struct f2fs_sb_info *sbi)
> __set_nat_cache_dirty(nm_i, ne);
> }
> update_nats_in_cursum(journal, -i);
> - up_write(&curseg->journal_rwsem);
> + write_unlock(&curseg->journal_rwlock);
> }
>
> static void __adjust_nat_entry_set(struct nat_entry_set *nes,
> @@ -2906,7 +2906,7 @@ static int __flush_nat_entry_set(struct f2fs_sb_info *sbi,
> to_journal = false;
>
> if (to_journal) {
> - down_write(&curseg->journal_rwsem);
> + write_lock(&curseg->journal_rwlock);
> } else {
> page = get_next_nat_page(sbi, start_nid);
> if (IS_ERR(page))
> @@ -2946,7 +2946,7 @@ static int __flush_nat_entry_set(struct f2fs_sb_info *sbi,
> }
>
> if (to_journal) {
> - up_write(&curseg->journal_rwsem);
> + write_unlock(&curseg->journal_rwlock);
> } else {
> __update_nat_bits(sbi, start_nid, page);
> f2fs_put_page(page, 1);
> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
> index f9b7fb785e1d..c397c1c271ec 100644
> --- a/fs/f2fs/segment.c
> +++ b/fs/f2fs/segment.c
> @@ -2442,9 +2442,9 @@ static void write_current_sum_page(struct f2fs_sb_info *sbi,
>
> mutex_lock(&curseg->curseg_mutex);
>
> - down_read(&curseg->journal_rwsem);
> + read_lock(&curseg->journal_rwlock);
> memcpy(&dst->journal, curseg->journal, SUM_JOURNAL_SIZE);
> - up_read(&curseg->journal_rwsem);
> + read_unlock(&curseg->journal_rwlock);
>
> memcpy(dst->entries, src->entries, SUM_ENTRY_SIZE);
> memcpy(&dst->footer, &src->footer, SUM_FOOTER_SIZE);
> @@ -3876,9 +3876,9 @@ static int read_normal_summaries(struct f2fs_sb_info *sbi, int type)
> mutex_lock(&curseg->curseg_mutex);
>
> /* update journal info */
> - down_write(&curseg->journal_rwsem);
> + write_lock(&curseg->journal_rwlock);
> memcpy(curseg->journal, &sum->journal, SUM_JOURNAL_SIZE);
> - up_write(&curseg->journal_rwsem);
> + write_unlock(&curseg->journal_rwlock);
>
> memcpy(curseg->sum_blk->entries, sum->entries, SUM_ENTRY_SIZE);
> memcpy(&curseg->sum_blk->footer, &sum->footer, SUM_FOOTER_SIZE);
> @@ -4136,7 +4136,7 @@ static void remove_sits_in_journal(struct f2fs_sb_info *sbi)
> struct f2fs_journal *journal = curseg->journal;
> int i;
>
> - down_write(&curseg->journal_rwsem);
> + write_lock(&curseg->journal_rwlock);
> for (i = 0; i < sits_in_cursum(journal); i++) {
> unsigned int segno;
> bool dirtied;
> @@ -4148,7 +4148,7 @@ static void remove_sits_in_journal(struct f2fs_sb_info *sbi)
> add_sit_entry(segno, &SM_I(sbi)->sit_entry_set);
> }
> update_sits_in_cursum(journal, -i);
> - up_write(&curseg->journal_rwsem);
> + write_unlock(&curseg->journal_rwlock);
> }
>
> /*
> @@ -4204,7 +4204,7 @@ void f2fs_flush_sit_entries(struct f2fs_sb_info *sbi, struct cp_control *cpc)
> to_journal = false;
>
> if (to_journal) {
> - down_write(&curseg->journal_rwsem);
> + write_lock(&curseg->journal_rwlock);
> } else {
> page = get_next_sit_page(sbi, start_segno);
> raw_sit = page_address(page);
> @@ -4251,7 +4251,7 @@ void f2fs_flush_sit_entries(struct f2fs_sb_info *sbi, struct cp_control *cpc)
> }
>
> if (to_journal)
> - up_write(&curseg->journal_rwsem);
> + write_unlock(&curseg->journal_rwlock);
> else
> f2fs_put_page(page, 1);
>
> @@ -4432,7 +4432,7 @@ static int build_curseg(struct f2fs_sb_info *sbi)
> array[i].sum_blk = f2fs_kzalloc(sbi, PAGE_SIZE, GFP_KERNEL);
> if (!array[i].sum_blk)
> return -ENOMEM;
> - init_rwsem(&array[i].journal_rwsem);
> + rwlock_init(&array[i].journal_rwlock);
> array[i].journal = f2fs_kzalloc(sbi,
> sizeof(struct f2fs_journal), GFP_KERNEL);
> if (!array[i].journal)
> @@ -4509,7 +4509,7 @@ static int build_sit_entries(struct f2fs_sb_info *sbi)
> start_blk += readed;
> } while (start_blk < sit_blk_cnt);
>
> - down_read(&curseg->journal_rwsem);
> + read_lock(&curseg->journal_rwlock);
> for (i = 0; i < sits_in_cursum(journal); i++) {
> unsigned int old_valid_blocks;
>
> @@ -4551,7 +4551,7 @@ static int build_sit_entries(struct f2fs_sb_info *sbi)
> old_valid_blocks;
> }
> }
> - up_read(&curseg->journal_rwsem);
> + read_unlock(&curseg->journal_rwlock);
>
> if (!err && total_node_blocks != valid_node_count(sbi)) {
> f2fs_err(sbi, "SIT is corrupted node# %u vs %u",
> diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
> index 050230c70a53..afb9041dc2e6 100644
> --- a/fs/f2fs/segment.h
> +++ b/fs/f2fs/segment.h
> @@ -306,7 +306,7 @@ struct victim_selection {
> struct curseg_info {
> struct mutex curseg_mutex; /* lock for consistency */
> struct f2fs_summary_block *sum_blk; /* cached summary block */
> - struct rw_semaphore journal_rwsem; /* protect journal area */
> + rwlock_t journal_rwlock; /* protect journal area */
> struct f2fs_journal *journal; /* cached journal info */
> unsigned char alloc_type; /* current allocation type */
> unsigned short seg_type; /* segment type like CURSEG_XXX_TYPE */
>