Re: [PATCH v3] f2fs: don't sleep while grabing nat_tree_lock

Jaegeuk Kim
2021-07-23T02:36:00Z

-> sleep to grab journal_rwsem by contention

checkpoint
- waiting for nat_tree_lock

In order to let checkpoint go, let's release nat_tree_lock, if there's a
journal_rwsem contention.

Signed-off-by: Daeho Jeong <daehojeong@google.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
---
Change log from v2:
- don't bother checkpoint

fs/f2fs/node.c | 17 +++++++++++++----
1 file changed, 13 insertions(+), 4 deletions(-)

diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
index 0be9e2d7120e..b26642daa3d2 100644
--- a/fs/f2fs/node.c
+++ b/fs/f2fs/node.c
@@ -552,7 +552,7 @@ int f2fs_get_node_info(struct f2fs_sb_info *sbi, nid_t nid,
int i;

ni->nid = nid;
-
+retry:
/* Check nat cache */
down_read(&nm_i->nat_tree_lock);
e = __lookup_nat_cache(nm_i, nid);
@@ -564,10 +564,19 @@ int f2fs_get_node_info(struct f2fs_sb_info *sbi, nid_t nid,
return 0;
}

- memset(&ne, 0, sizeof(struct f2fs_nat_entry));
+ /*
+ * Check current segment summary by trying to grab journal_rwsem first.
+ * This sem is on the critical path on the checkpoint requiring the above
+ * nat_tree_lock. Therefore, we should retry, if we failed to grab here
+ * while not bothering checkpoint.
+ */
+ if (rwsem_is_locked(&sbi->cp_global_sem)) {
+ down_read(&curseg->journal_rwsem);
+ } else if (!down_read_trylock(&curseg->journal_rwsem)) {
+ up_read(&nm_i->nat_tree_lock);
+ goto retry;
+ }

- /* Check current segment summary */
- down_read(&curseg->journal_rwsem);
i = f2fs_lookup_journal_in_cursum(journal, NAT_JOURNAL, nid, 0);
if (i >= 0) {
ne = nat_in_journal(journal, i);
--
2.32.0.432.gabb21c7263-goog