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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: Daeho Jeong <daehojeong@google.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
This commit is contained in:
Jaegeuk Kim 2021-07-22 10:30:58 -07:00
parent 6de8687ccd
commit 2eeb0dce72
1 changed files with 13 additions and 4 deletions
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17
fs/f2fs/node.c
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@ -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);