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(cst-prg-14-82.cust.vodafone.cz. [46.135.14.82]) by smtp.gmail.com with ESMTPSA id 4fb4d7f45d1cf-63e7ef82b6esm12043982a12.11.2025.10.29.06.55.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 29 Oct 2025 06:55:42 -0700 (PDT) From: Mateusz Guzik To: brauner@kernel.org Cc: viro@zeniv.linux.org.uk, jack@suse.cz, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Mateusz Guzik Subject: [WIP RFC PATCH] fs: hide names_cachep behind runtime_const machinery Date: Wed, 29 Oct 2025 14:55:38 +0100 Message-ID: <20251029135538.658951-1-mjguzik@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" All path lookups end up allocating and freeing a buffer. The namei cache is created and at boot time and remains constant, meaning there is no reason to spend a cacheline to load the pointer. I verified this boots on x86-64. The problem is that when building I get the following: ld: warning: orphan section `runtime_ptr_names_cachep' from `vmlinux.o' bei= ng placed in section `runtime_ptr_names_cachep' I don't know what's up with that yet, but I will sort it out. Before I put any effort into it I need to know if the idea looks fine. --- fs/dcache.c | 1 + include/linux/fs.h | 5 +++-- 2 files changed, 4 insertions(+), 2 deletions(-) diff --git a/fs/dcache.c b/fs/dcache.c index 035cccbc9276..786d09798313 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -3265,6 +3265,7 @@ void __init vfs_caches_init(void) { names_cachep =3D kmem_cache_create_usercopy("names_cache", PATH_MAX, 0, SLAB_HWCACHE_ALIGN|SLAB_PANIC, 0, PATH_MAX, NULL); + runtime_const_init(ptr, names_cachep); =20 dcache_init(); inode_init(); diff --git a/include/linux/fs.h b/include/linux/fs.h index 68c4a59ec8fb..08ea27340309 100644 --- a/include/linux/fs.h +++ b/include/linux/fs.h @@ -2960,8 +2960,9 @@ extern void __init vfs_caches_init(void); =20 extern struct kmem_cache *names_cachep; =20 -#define __getname() kmem_cache_alloc(names_cachep, GFP_KERNEL) -#define __putname(name) kmem_cache_free(names_cachep, (void *)(name)) +#define __const_names_cachep runtime_const_ptr(names_cachep) +#define __getname() kmem_cache_alloc(__const_names_cachep, GFP_KERNEL) +#define __putname(name) kmem_cache_free(__const_names_cachep, (void *)(na= me)) =20 extern struct super_block *blockdev_superblock; static inline bool sb_is_blkdev_sb(struct super_block *sb) --=20 2.34.1