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McKenney" , Frederic Weisbecker , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , Boqun Feng , Zqiang , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , rcu@vger.kernel.org, linux-mm@kvack.org, Alexander Viro , Christian Brauner , Jan Kara Subject: [PATCH 2/8] fs/dcache: use rcu_ptr instead of rcu_head for external names Date: Thu, 16 Apr 2026 18:10:16 +0900 Message-ID: <20260416091022.36823-3-harry@kernel.org> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20260416091022.36823-1-harry@kernel.org> References: <20260416091022.36823-1-harry@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: E98681A0003 X-Stat-Signature: xpfqpwpwg9qnnyswbjjfbmr5u3chpkgn X-Rspam-User: X-HE-Tag: 1776330635-785144 X-HE-Meta: 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 JttwLH5G wYkHQQcb8wdanQoEXtKN+hu8QgnXjlc9VvmaSTrxxvF0HMvHBIRtyZoUfAAR1bzUSIcwmwAkfQ4iQfCZ8L+jaQx/SGaFRsQs4+Uua1+Urd2bsFx/eQJH86WQO8bHgo0NFX6+z/1+4NrqrxvFsDG6y/nhGAXvJr8TsoxwFngg5xrW92+ZGqkqrZC9DgAOgckz0K5nbm4t40odzV7zBNd6ihFyJLJZ5MzZFI5Wr+8vax/bFmIGttjhAYVKSJ/lCYQve65UWj4HPjlF+iGHlBqfscXg80+2jFvpH4KNpnztIZXCh6u8RBkhCQITKvT7hn9757Drngw0W0mgDKT+zzQGO1Ak4Mg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: When a file name length exceeds 31 (DCACHE_INLINE_LEN-1), struct external_name is dynamically allocated. Because only kfree_rcu() is used to free the objects, struct rcu_ptr is enough and saves a pointer per object. Under the author's home directory, there are 230k unique file names that are longer than 31. Some memory saving benefit is expected. Cc: Alexander Viro Cc: Christian Brauner Cc: Jan Kara Signed-off-by: Harry Yoo (Oracle) --- fs/dcache.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/fs/dcache.c b/fs/dcache.c index 7ba1801d8132..fa37e3964b38 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -325,12 +325,12 @@ static inline int dentry_cmp(const struct dentry *dentry, const unsigned char *c /* * long names are allocated separately from dentry and never modified. * Refcounted, freeing is RCU-delayed. See take_dentry_name_snapshot() - * for the reason why ->count and ->head can't be combined into a union. + * for the reason why ->count and ->rcu can't be combined into a union. * dentry_string_cmp() relies upon ->name[] being word-aligned. */ struct external_name { atomic_t count; - struct rcu_head head; + struct rcu_ptr rcu; unsigned char name[] __aligned(sizeof(unsigned long)); }; @@ -393,7 +393,7 @@ void release_dentry_name_snapshot(struct name_snapshot *name) struct external_name *p; p = container_of(name->name.name, struct external_name, name[0]); if (unlikely(atomic_dec_and_test(&p->count))) - kfree_rcu(p, head); + kfree_rcu(p, rcu); } } EXPORT_SYMBOL(release_dentry_name_snapshot); @@ -2863,7 +2863,7 @@ static void copy_name(struct dentry *dentry, struct dentry *target) dentry->__d_name.hash_len = target->__d_name.hash_len; } if (old_name && likely(atomic_dec_and_test(&old_name->count))) - kfree_rcu(old_name, head); + kfree_rcu(old_name, rcu); } /* -- 2.43.0