linux-ext4 - [RFC PATCH V3 2/7] ext4: specify the free pointer offset for ext4_inode

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Message-ID: <20251027122847.320924-3-harry.yoo@oracle.com>
Date: Mon, 27 Oct 2025 21:28:42 +0900
From: Harry Yoo <harry.yoo@...cle.com>
To: akpm@...ux-foundation.org, vbabka@...e.cz
Cc: andreyknvl@...il.com, cl@...ux.com, dvyukov@...gle.com, glider@...gle.com,
        hannes@...xchg.org, linux-mm@...ck.org, mhocko@...nel.org,
        muchun.song@...ux.dev, rientjes@...gle.com, roman.gushchin@...ux.dev,
        ryabinin.a.a@...il.com, shakeel.butt@...ux.dev, surenb@...gle.com,
        vincenzo.frascino@....com, yeoreum.yun@....com, harry.yoo@...cle.com,
        tytso@....edu, adilger.kernel@...ger.ca, linux-ext4@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [RFC PATCH V3 2/7] ext4: specify the free pointer offset for ext4_inode_cache

Convert ext4_inode_cache to use the kmem_cache_args interface and
specify a free pointer offset.

Since ext4_inode_cache uses a constructor, the free pointer would be
placed after the object to overwriting fields used by the constructor.
However, some fields such as ->i_flags are not used by the constructor
and can safely be repurposed for the free pointer.

Specify the free pointer offset at i_flags to reduce the object size.

Signed-off-by: Harry Yoo <harry.yoo@...cle.com>
---
 fs/ext4/super.c | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 699c15db28a8..2860e0ee913f 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1474,12 +1474,20 @@ static void init_once(void *foo)
 
 static int __init init_inodecache(void)
 {
-	ext4_inode_cachep = kmem_cache_create_usercopy("ext4_inode_cache",
-				sizeof(struct ext4_inode_info), 0,
-				SLAB_RECLAIM_ACCOUNT | SLAB_ACCOUNT,
-				offsetof(struct ext4_inode_info, i_data),
-				sizeof_field(struct ext4_inode_info, i_data),
-				init_once);
+	struct kmem_cache_args args = {
+		.align = 0,
+		.useroffset = offsetof(struct ext4_inode_info, i_data),
+		.usersize = sizeof_field(struct ext4_inode_info, i_data),
+		.use_freeptr_offset = true,
+		.freeptr_offset = offsetof(struct ext4_inode_info, i_flags),
+		.ctor = init_once,
+	};
+
+	ext4_inode_cachep = kmem_cache_create("ext4_inode_cache",
+				sizeof(struct ext4_inode_info),
+				&args,
+				SLAB_RECLAIM_ACCOUNT | SLAB_ACCOUNT);
+
 	if (ext4_inode_cachep == NULL)
 		return -ENOMEM;
 	return 0;
-- 
2.43.0