Messages in this thread Patch in this message | | | Date | Thu, 22 Jul 2021 10:44:28 -0700 | From | Jaegeuk Kim <> | Subject | Re: [PATCH v2] f2fs: don't sleep while grabing nat_tree_lock |
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This tries to fix priority inversion in the below condition resulting in long checkpoint delay.
f2fs_get_node_info() - nat_tree_lock -> 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: Jaegeuk Kim <jaegeuk@kernel.org> --- Change log from v1: - drop rwlock but take retry logic to reduce lock-holding time
fs/f2fs/node.c | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-)
diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c index 0be9e2d7120e..c60ba4179bb2 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 +564,16 @@ 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. + */ + 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
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