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b=eCXMwYc2z4yu4J+0Jx9PtjUmryGPi66pBWmBwUHGkSsOw9DA77jsZqGsM9dPhAwdg OhOZSxqmDJpUEFh58rH2Z7UCzGNnGMjcLn981RQoeEbHXf3tnHTpmDH4P3bVEdG0o+ D7/fqFQnu+MOUl89PM5at3bR1MNVSY1xeWa9GPYBRQGE+byY9GVkTgbFrPmBxG+WnJ 6KC/9FF6LS4eREb7x5X9XCVaRRfykuVMtfjSP3Mm5z3u4HRd590jkravzhzC7Uexit 8e1ngQZlW3jPhcle4rC03ov+xA7q64bu/cNyHvNB2Lq7LUYM0VU7nI+/7YCDxA01k1 /JJWsGUx95+0A== Message-ID: From: sashiko-bot@kernel.org Subject: Re: [PATCH RFC v2 2/8] mm, slab: introduce slab_debug=N Reply-To: sashiko-reviews@lists.linux.dev To: =?utf-8?b?Vmxhc3RpbWlsIEJhYmthIChTVVNFKQ==?= , "Harry Yoo" Cc: "Hao Li" , "Christoph Lameter" , "David Rientjes" , "Roman Gushchin" , "Geert Uytterhoeven" , "Conor Dooley" , "Damien Le Moal" , linux-mm@kvack.org In-Reply-To: <20261024-slub_tiny_rework-v2-2-bf1419ab5ffd@kernel.org> References: <20261024-slub_tiny_rework-v2-0-bf1419ab5ffd@kernel.org> <20261024-slub_tiny_rework-v2-2-bf1419ab5ffd@kernel.org> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Date: Sat, 24 Oct 2026 19:22:54 +0000 X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 3C07980003 X-Stat-Signature: 1iugazw7dm4pekfo8kqs8mq7imne39fh X-Rspam-User: X-Spam-Status: No, score=-11.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-HE-Tag: 1792869777-734852 X-HE-Meta: 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 LwXgtQe+ 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 X-Archived-By: Thank you for your contribution! Sashiko AI review found 1 potential issue(= s) to consider: - [Medium] mm, slab: missing SLAB_DEBUG_NOOP in SLAB_MERGE_SAME merges mism= atched caches -- commit 2d842bc4bf4f28b2b4c86a9001856691abe3624c Author: Vlastimil Babka (SUSE) mm, slab: introduce slab_debug=3DN This commit introduces the slab_debug=3DN boot option and the corresponding SLAB_DEBUG_NOOP slab flag to force slab debugging slowpaths and disable percpu sheaf caching without enabling actual debug checks. It also excludes SLAB_DEBUG_NOOP from SLAB_NEVER_MERGE and avoids disabling printk pointer hashing when only SLAB_DEBUG_NOOP is enabled. > diff --git a/mm/slab_common.c b/mm/slab_common.c > index 01c64ef661e7f..02dfe4351e8b7 100644 > --- a/mm/slab_common.c > +++ b/mm/slab_common.c > @@ -47,9 +47,9 @@ struct kmem_cache *kmem_cache; > * Any flag that adds per-object metadata should be included, > * since slab merging can update s->inuse that affects the metadata layo= ut. > */ > -#define SLAB_NEVER_MERGE (SLAB_DEBUG_FLAGS | SLAB_TYPESAFE_BY_RCU | \ > - SLAB_NOLEAKTRACE | SLAB_FAILSLAB | SLAB_NO_MERGE | \ > - SLAB_OBJ_EXT_IN_OBJ) > +#define SLAB_NEVER_MERGE ((SLAB_DEBUG_FLAGS & ~SLAB_DEBUG_NOOP) | \ > + SLAB_TYPESAFE_BY_RCU | SLAB_NOLEAKTRACE | SLAB_FAILSLAB | \ > + SLAB_NO_MERGE | SLAB_OBJ_EXT_IN_OBJ) > =20 > #define SLAB_MERGE_SAME (SLAB_RECLAIM_ACCOUNT | SLAB_CACHE_DMA | \ > SLAB_CACHE_DMA32 | SLAB_ACCOUNT | SLAB_MAY_ACCOUNT) [Severity: Medium] Should SLAB_DEBUG_NOOP also be added to SLAB_MERGE_SAME? Excluding SLAB_DEBUG_NOOP from SLAB_NEVER_MERGE allows caches with SLAB_DEBUG_NOOP to participate in slab merging, which is checked in find_mergeable(): mm/slab_common.c:find_mergeable() { flags =3D kmem_cache_flags(flags, name); if (slab_args_unmergeable(args, flags)) return NULL; ... list_for_each_entry_reverse(s, &slab_caches, list) { if (slab_unmergeable(s)) continue; if (size > s->size) continue; if ((flags & SLAB_MERGE_SAME) !=3D (s->flags & SLAB_MERGE_SAME)) continue; } When SLAB_DEBUG_NOOP is enabled for a subset of caches (for example via per-cache boot parameters such as slab_debug=3DN, or slab_debug=3DN;-,, or by passing SLAB_DEBUG_NOOP to kmem_cache_create()), find_mergeable() does not require both caches to agree on SLAB_DEBUG_NOOP. As a result, a cache matched by slab_debug=3DN, can merge into = an existing compatible cache created without SLAB_DEBUG_NOOP (such as a kmalloc-* cache), keeping percpu sheaves enabled and silently ignoring the requested option. Conversely, if an earlier mergeable cache is created with SLAB_DEBUG_NOOP, subsequent compatible caches without SLAB_DEBUG_NOOP will merge into it and be forced onto the debug slowpaths with zero sheaf capacity. If SLAB_DEBUG_NOOP is added to SLAB_MERGE_SAME, does create_unique_id() in mm/slub.c also need to encode SLAB_DEBUG_NOOP so that aliasable caches differing only in SLAB_DEBUG_NOOP do not generate colliding sysfs IDs in sysfs_slab_add()? mm/slub.c:create_unique_id() { /* * First flags affecting slabcache operations. We will only * get here for aliasable slabs so we do not need to support * too many flags. The flags here must cover all flags that * are matched during merging to guarantee that the id is * unique. */ if (s->flags & SLAB_CACHE_DMA) *p++ =3D 'd'; if (s->flags & SLAB_CACHE_DMA32) *p++ =3D 'D'; if (s->flags & SLAB_RECLAIM_ACCOUNT) *p++ =3D 'a'; if (s->flags & SLAB_CONSISTENCY_CHECKS) *p++ =3D 'F'; if (s->flags & SLAB_ACCOUNT) *p++ =3D 'A'; } --=20 Sashiko AI review =C2=B7 https://sashiko.dev/#/patchset/20261024-slub_tiny_= rework-v2-0-bf1419ab5ffd@kernel.org?part=3D2