f2fs: avoid high cpu usage in discard thread

We take very long time to finish generic/476, this is because we will check consistence of all discard entries in global rb tree while traversing all different granularity pending lists, even when the list is empty, in order to avoid that unneeded overhead, we have to skip the check when coming up an empty list. generic/476 time consumption: cost Before patch & w/o consistence check 57s Before patch & w/ consistence check 1426s After patch 78s Signed-off-by: Chao Yu <[email protected]> Signed-off-by: Jaegeuk Kim <[email protected]>
kyagi · Jan 16, 2018 · 49c60c6 · 49c60c6
1 parent 94b1e10
commit 49c60c6
Showing 1 changed file with 3 additions and 0 deletions.
diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
@@ -1204,6 +1204,8 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
 		pend_list = &dcc->pend_list[i];
 
 		mutex_lock(&dcc->cmd_lock);
+		if (list_empty(pend_list))
+			goto next;
 		f2fs_bug_on(sbi, !__check_rb_tree_consistence(sbi, &dcc->root));
 		blk_start_plug(&plug);
 		list_for_each_entry_safe(dc, tmp, pend_list, list) {
@@ -1222,6 +1224,7 @@ static int __issue_discard_cmd(struct f2fs_sb_info *sbi,
 				break;
 		}
 		blk_finish_plug(&plug);
+next:
 		mutex_unlock(&dcc->cmd_lock);
 
 		if (iter >= dpolicy->max_requests)