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AJvYcCWjkgsXfm5eqRmThX7hJ2E2z8DGJgE5tdFIhRign2YHf2NkIFTdcNMDcmUj2Mk+kR9eK1h8kM15Gw==@kvack.org X-Gm-Message-State: AOJu0YxGLnm9Hk1PIMJjDdcVHyIpWWVZDt0zjL/m+UkcaFqbmnHFg9pc nLZmd6dwrE65l0BkuGsQfu8AXb2GsYjKf0TNgiCBl035yFEtNY/T7f9ROU2d5Z+tSASQ2qgNkTv Dbx5kKct+HJo0vjyIzCOgePbQTFMa6zvioMDdSEkA X-Gm-Gg: ASbGncsCgccUoeyDd2jP0wYKn66KmiiyV4aMdvY9V2D0/walmKZSZ5uqj7oAfpU39J0 Axthq3DopiuTxaUsKYsu7vBaBlqly1WVgYkpzwp+WGXjNieruyhIGqOClioJZhayPlPuTIgUy5y cZPmLl+u+Z8IG0DDODbpRtvi9MwhA9pugFy/0cGG9v7idE/RU797aUP0kJGBQN0I0k+FU6GlE4w CBjoRFinEAbJjjKIVufn7xzFmDMO4dRaCHUucCGgWeb6vMeGZj31Kk= X-Google-Smtp-Source: AGHT+IEZX3AIsjneqU2jkzMxfJ1rwKeMkyXol2y5mWE/WbUduMbZkhlHGcC/mN/j9JEB5vlP4XKLW47PV44WdfJ9t1E= X-Received: by 2002:a05:622a:38c:b0:4b7:9b7a:1cfc with SMTP id d75a77b69052e-4da2d8fb31emr8186661cf.10.1758816901473; Thu, 25 Sep 2025 09:15:01 -0700 (PDT) MIME-Version: 1.0 References: <20250910-slub-percpu-caches-v8-0-ca3099d8352c@suse.cz> <20250910-slub-percpu-caches-v8-7-ca3099d8352c@suse.cz> In-Reply-To: <20250910-slub-percpu-caches-v8-7-ca3099d8352c@suse.cz> From: Suren Baghdasaryan Date: Thu, 25 Sep 2025 09:14:50 -0700 X-Gm-Features: AS18NWAvEId5a1XW0xii0HqSmARldJg6moJt7e5uwfO2hVBiihb1I0PmhdfuWc8 Message-ID: Subject: Re: [PATCH v8 07/23] slab: skip percpu sheaves for remote object freeing To: Vlastimil Babka Cc: "Liam R. Howlett" , Christoph Lameter , David Rientjes , Roman Gushchin , Harry Yoo , Uladzislau Rezki , Sidhartha Kumar , linux-mm@kvack.org, linux-kernel@vger.kernel.org, rcu@vger.kernel.org, maple-tree@lists.infradead.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: td7xq5zs158dx48zauay88m7ssc77eud X-Rspam-User: X-Rspamd-Queue-Id: AACA0C000D X-Rspamd-Server: rspam04 X-HE-Tag: 1758816903-239552 X-HE-Meta: U2FsdGVkX1/3cLHS7X2hfZbtrgTl+Ng5cfpR+N3136ZlE8l6PsyBBakZ2JpD/hINjs52gddWbBAf11q3IlvhaINxVqFSpzu0yy92+8LnALnj3A1ikZjPdE2ud/TEY9LBh1Gx9EKmYdk7wqPXp1GKOagQZw2I/wAmntUXlABIL3SayuzJgG6eTsu4Y8jx9NM2Posi6LHdyucL/iAPbMIFfI/O5PKjULGE8gr8WopaZH6XowQRHeOg0SP9vN7aSwfsuiuLXn+ZXTMA3ClMPz9OHIwsuwh4p8VGFs6tkfpE1uckya3cicCIp4uf2BVJJ1Ti2i1nK3pSDzuLKuul/sLmv50ANn5KqXfOsiEAyu+YVqQ9W7GTb2Aqj29bX+ZLSaOKiszlsmKsjqUZGoeHOdcfFZ4NRrRwvNrkprraf3KV4jNSVPzpWRbhZ1u4b9nlHXJoUnGmE5FQf6u1BsLgxTuFSWFb6GTzk4emz1GWhUgGeanVNbMirbtaKLNCvdD8nzKhP50/ZQozWsng0SvcuF/5T3gqFZOqHx3GVEmQev9lS/omBZ00VcYvX6wC75UjHqC3u0wQwTWzkxS/ruoanwghllmav8WcM5Y+4h9MW0OUPgUN/b8pz827mMNkeG1MQGLYjS4c97HpcWkdZIDgOwaloriCS5N9/AOB0Kp46Yzzu7SbtGx5OrWltXdSDHZE8QlNedfkwa2JykeqMJWqMpOe4n4mv9oUG6y8f6bcmBewoGWTXYZxgwVhNC3AktTHIuGtxZqQP5R8v8GspCDd1P0gApzCQndmr4w8pA1YEWtDE1f8pZ0xFwqlcXDw3jmxi7j+SJwkjvIOPmeXHGMu54WyyiTPd74H4wtgeFUdDpblVnBFCM8A2nB6czBcuMblXqvWpMsyAhfCj2uEb7QRqBGSnAxPfKrm2gmC2RJWvtKi/KCWwaPQesgxsXVbW4eR4LfzQ5YlZVMM0JpSbmiF1UV lNp+bH2d hDDs7o+y902L+8HzoMrfGABn1GECcg7zpoYwu7cqo80aix8y5huQ7z6Fa20PcJj0YPeniFRInkHOZm1aVZEvXoJegkQcwTGQ//UlR8jROlHdBiTCRu01NbUzV88IhR1No8HGY1W2PXgKmTzoscOnFeGP82x/dCKT1qP21zqeGRIHkNbRqglhBkXKwFwxxv9H30p6xTGhalArIzIc= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Sep 10, 2025 at 1:01=E2=80=AFAM Vlastimil Babka wr= ote: > > Since we don't control the NUMA locality of objects in percpu sheaves, > allocations with node restrictions bypass them. Allocations without > restrictions may however still expect to get local objects with high > probability, and the introduction of sheaves can decrease it due to > freed object from a remote node ending up in percpu sheaves. > > The fraction of such remote frees seems low (5% on an 8-node machine) > but it can be expected that some cache or workload specific corner cases > exist. We can either conclude that this is not a problem due to the low > fraction, or we can make remote frees bypass percpu sheaves and go > directly to their slabs. This will make the remote frees more expensive, > but if if's only a small fraction, most frees will still benefit from s/if's/it's > the lower overhead of percpu sheaves. > > This patch thus makes remote object freeing bypass percpu sheaves, > including bulk freeing, and kfree_rcu() via the rcu_free sheaf. However > it's not intended to be 100% guarantee that percpu sheaves will only > contain local objects. The refill from slabs does not provide that > guarantee in the first place, and there might be cpu migrations > happening when we need to unlock the local_lock. Avoiding all that could > be possible but complicated so we can leave it for later investigation > whether it would be worth it. It can be expected that the more selective > freeing will itself prevent accumulation of remote objects in percpu > sheaves so any such violations would have only short-term effects. > > Reviewed-by: Harry Yoo > Signed-off-by: Vlastimil Babka Reviewed-by: Suren Baghdasaryan > --- > mm/slab_common.c | 7 +++++-- > mm/slub.c | 42 ++++++++++++++++++++++++++++++++++++------ > 2 files changed, 41 insertions(+), 8 deletions(-) > > diff --git a/mm/slab_common.c b/mm/slab_common.c > index 005a4319c06a01d2b616a75396fcc43766a62ddb..b6601e0fe598e24bd8d456dce= 4fc82c65b342bfd 100644 > --- a/mm/slab_common.c > +++ b/mm/slab_common.c > @@ -1623,8 +1623,11 @@ static bool kfree_rcu_sheaf(void *obj) > > slab =3D folio_slab(folio); > s =3D slab->slab_cache; > - if (s->cpu_sheaves) > - return __kfree_rcu_sheaf(s, obj); > + if (s->cpu_sheaves) { > + if (likely(!IS_ENABLED(CONFIG_NUMA) || > + slab_nid(slab) =3D=3D numa_mem_id())) > + return __kfree_rcu_sheaf(s, obj); > + } > > return false; > } > diff --git a/mm/slub.c b/mm/slub.c > index 35274ce4e709c9da7ac8f9006c824f28709e923d..9699d048b2cd08ee75c4cc3d1= e460868704520b1 100644 > --- a/mm/slub.c > +++ b/mm/slub.c > @@ -472,6 +472,7 @@ struct slab_sheaf { > }; > struct kmem_cache *cache; > unsigned int size; > + int node; /* only used for rcu_sheaf */ > void *objects[]; > }; > > @@ -5828,7 +5829,7 @@ static void rcu_free_sheaf(struct rcu_head *head) > */ > __rcu_free_sheaf_prepare(s, sheaf); > > - barn =3D get_node(s, numa_mem_id())->barn; > + barn =3D get_node(s, sheaf->node)->barn; > > /* due to slab_free_hook() */ > if (unlikely(sheaf->size =3D=3D 0)) > @@ -5914,10 +5915,12 @@ bool __kfree_rcu_sheaf(struct kmem_cache *s, void= *obj) > > rcu_sheaf->objects[rcu_sheaf->size++] =3D obj; > > - if (likely(rcu_sheaf->size < s->sheaf_capacity)) > + if (likely(rcu_sheaf->size < s->sheaf_capacity)) { > rcu_sheaf =3D NULL; > - else > + } else { > pcs->rcu_free =3D NULL; > + rcu_sheaf->node =3D numa_mem_id(); > + } > > local_unlock(&s->cpu_sheaves->lock); > > @@ -5944,7 +5947,11 @@ static void free_to_pcs_bulk(struct kmem_cache *s,= size_t size, void **p) > bool init =3D slab_want_init_on_free(s); > unsigned int batch, i =3D 0; > struct node_barn *barn; > + void *remote_objects[PCS_BATCH_MAX]; > + unsigned int remote_nr =3D 0; > + int node =3D numa_mem_id(); > > +next_remote_batch: > while (i < size) { > struct slab *slab =3D virt_to_slab(p[i]); > > @@ -5954,7 +5961,15 @@ static void free_to_pcs_bulk(struct kmem_cache *s,= size_t size, void **p) > if (unlikely(!slab_free_hook(s, p[i], init, false))) { > p[i] =3D p[--size]; > if (!size) > - return; > + goto flush_remote; > + continue; > + } > + > + if (unlikely(IS_ENABLED(CONFIG_NUMA) && slab_nid(slab) != =3D node)) { > + remote_objects[remote_nr] =3D p[i]; > + p[i] =3D p[--size]; > + if (++remote_nr >=3D PCS_BATCH_MAX) > + goto flush_remote; > continue; > } > > @@ -6024,6 +6039,15 @@ static void free_to_pcs_bulk(struct kmem_cache *s,= size_t size, void **p) > */ > fallback: > __kmem_cache_free_bulk(s, size, p); > + > +flush_remote: > + if (remote_nr) { > + __kmem_cache_free_bulk(s, remote_nr, &remote_objects[0]); > + if (i < size) { > + remote_nr =3D 0; > + goto next_remote_batch; > + } > + } > } > > #ifndef CONFIG_SLUB_TINY > @@ -6115,8 +6139,14 @@ void slab_free(struct kmem_cache *s, struct slab *= slab, void *object, > if (unlikely(!slab_free_hook(s, object, slab_want_init_on_free(s)= , false))) > return; > > - if (!s->cpu_sheaves || !free_to_pcs(s, object)) > - do_slab_free(s, slab, object, object, 1, addr); > + if (s->cpu_sheaves && likely(!IS_ENABLED(CONFIG_NUMA) || > + slab_nid(slab) =3D=3D numa_mem_id())= ) { > + if (likely(free_to_pcs(s, object))) { nit: no need for curly braces here. > + return; > + } > + } > + > + do_slab_free(s, slab, object, object, 1, addr); > } > > #ifdef CONFIG_MEMCG > > -- > 2.51.0 >