linux-kernel - [PATCH] f2fs: avoid unneeded memory allocation in __add_ino

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Date:   Fri,  6 Aug 2021 08:05:58 +0800
From:   Chao Yu <chao@...nel.org>
To:     jaegeuk@...nel.org
Cc:     linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, Chao Yu <chao.yu@...ux.dev>,
        Chao Yu <chao@...nel.org>
Subject: [PATCH] f2fs: avoid unneeded memory allocation in __add_ino_entry()

__add_ino_entry() will allocate slab cache even if we have already
cached ino entry in radix tree, e.g. for case of multiple devices.

Let's check radix tree first under protection of rcu lock to see
whether we need to do slab allocation, it will mitigate memory
pressure from "f2fs_ino_entry" slab cache.

Signed-off-by: Chao Yu <chao@...nel.org>
---
 fs/f2fs/checkpoint.c | 22 +++++++++++++++++-----
 1 file changed, 17 insertions(+), 5 deletions(-)

diff --git a/fs/f2fs/checkpoint.c b/fs/f2fs/checkpoint.c
index 7f6745f4630e..5b6ddeae1107 100644
--- a/fs/f2fs/checkpoint.c
+++ b/fs/f2fs/checkpoint.c
@@ -465,16 +465,28 @@ static void __add_ino_entry(struct f2fs_sb_info *sbi, nid_t ino,
 						unsigned int devidx, int type)
 {
 	struct inode_management *im = &sbi->im[type];
-	struct ino_entry *e, *tmp;
+	struct ino_entry *e = NULL, *new = NULL;
+
+	if (type == FLUSH_INO) {
+		rcu_read_lock();
+		e = radix_tree_lookup(&im->ino_root, ino);
+		rcu_read_unlock();
+	}
 
-	tmp = f2fs_kmem_cache_alloc(ino_entry_slab, GFP_NOFS);
+retry:
+	if (!e)
+		new = f2fs_kmem_cache_alloc(ino_entry_slab, GFP_NOFS);
 
 	radix_tree_preload(GFP_NOFS | __GFP_NOFAIL);
 
 	spin_lock(&im->ino_lock);
 	e = radix_tree_lookup(&im->ino_root, ino);
 	if (!e) {
-		e = tmp;
+		if (!new) {
+			spin_unlock(&im->ino_lock);
+			goto retry;
+		}
+		e = new;
 		if (unlikely(radix_tree_insert(&im->ino_root, ino, e)))
 			f2fs_bug_on(sbi, 1);
 
@@ -492,8 +504,8 @@ static void __add_ino_entry(struct f2fs_sb_info *sbi, nid_t ino,
 	spin_unlock(&im->ino_lock);
 	radix_tree_preload_end();
 
-	if (e != tmp)
-		kmem_cache_free(ino_entry_slab, tmp);
+	if (new && e != new)
+		kmem_cache_free(ino_entry_slab, new);
 }
 
 static void __remove_ino_entry(struct f2fs_sb_info *sbi, nid_t ino, int type)
-- 
2.22.1