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Wed, 11 Aug 2021 04:19:50 -0700 (PDT) Received: from localhost.localdomain ([139.177.225.255]) by smtp.gmail.com with ESMTPSA id o9sm29513925pfh.217.2021.08.11.04.19.47 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Wed, 11 Aug 2021 04:19:50 -0700 (PDT) From: Muchun Song To: cl@linux.com, penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, akpm@linux-foundation.org, vbabka@suse.cz Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Muchun Song Subject: [PATCH] mm: slub: remove preemption disabling from put_cpu_partial Date: Wed, 11 Aug 2021 19:19:21 +0800 Message-Id: <20210811111921.85999-1-songmuchun@bytedance.com> X-Mailer: git-send-email 2.21.0 (Apple Git-122) MIME-Version: 1.0 X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 331D4100BFA9 Authentication-Results: imf13.hostedemail.com; dkim=pass header.d=bytedance-com.20150623.gappssmtp.com header.s=20150623 header.b=B8uEqYdm; dmarc=pass (policy=none) header.from=bytedance.com; spf=pass (imf13.hostedemail.com: domain of songmuchun@bytedance.com designates 209.85.216.54 as permitted sender) smtp.mailfrom=songmuchun@bytedance.com X-Stat-Signature: gyff9h8qtb41qzgmuckmrtbbpheoc5sc X-HE-Tag: 1628680792-822528 Content-Transfer-Encoding: quoted-printable 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: The commit d6e0b7fa1186 ("slub: make dead caches discard free slabs immediately") introduced those logic to speed up the destruction of per-memcg kmem caches, because kmem caches created for a memory cgroup are only destroyed after the last page charged to the cgroup is freed at that time. But since commit 9855609bde03 ("mm: memcg/slab: use a single set of kmem_caches for all accounted allocations), we do not have per-memcg kmem caches anymore. Are those code pointless? No, the kmem_cache->cpu_partial can be set to zero by 'echo 0 > /sys/ kernel/slab/*/cpu_partial'. In this case, the slab page will be put into cpu partial list and then moved to node list (because slub_cpu_partial() returns zero). However, we can skip putting the slab page to cpu partial list and just move it to node list directly. We can adjust the condition of kmem_cache_has_cpu_partial() to slub_cpu_partial() in __slab_free() and remove those code from put_cpu_partial() for simplification. Signed-off-by: Muchun Song --- mm/slub.c | 23 +++-------------------- 1 file changed, 3 insertions(+), 20 deletions(-) diff --git a/mm/slub.c b/mm/slub.c index b6c5205252eb..69c8ada322a0 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -2438,7 +2438,6 @@ static void put_cpu_partial(struct kmem_cache *s, s= truct page *page, int drain) int pages; int pobjects; =20 - preempt_disable(); do { pages =3D 0; pobjects =3D 0; @@ -2470,16 +2469,7 @@ static void put_cpu_partial(struct kmem_cache *s, = struct page *page, int drain) page->pobjects =3D pobjects; page->next =3D oldpage; =20 - } while (this_cpu_cmpxchg(s->cpu_slab->partial, oldpage, page) - !=3D oldpage); - if (unlikely(!slub_cpu_partial(s))) { - unsigned long flags; - - local_irq_save(flags); - unfreeze_partials(s, this_cpu_ptr(s->cpu_slab)); - local_irq_restore(flags); - } - preempt_enable(); + } while (this_cpu_cmpxchg(s->cpu_slab->partial, oldpage, page) !=3D old= page); #endif /* CONFIG_SLUB_CPU_PARTIAL */ } =20 @@ -3059,9 +3049,7 @@ static void __slab_free(struct kmem_cache *s, struc= t page *page, was_frozen =3D new.frozen; new.inuse -=3D cnt; if ((!new.inuse || !prior) && !was_frozen) { - - if (kmem_cache_has_cpu_partial(s) && !prior) { - + if (slub_cpu_partial(s) && !prior) { /* * Slab was on no list before and will be * partially empty @@ -3069,9 +3057,7 @@ static void __slab_free(struct kmem_cache *s, struc= t page *page, * freeze it. */ new.frozen =3D 1; - } else { /* Needs to be taken off a list */ - n =3D get_node(s, page_to_nid(page)); /* * Speculatively acquire the list_lock. @@ -3082,17 +3068,14 @@ static void __slab_free(struct kmem_cache *s, str= uct page *page, * other processors updating the list of slabs. */ spin_lock_irqsave(&n->list_lock, flags); - } } - } while (!cmpxchg_double_slab(s, page, prior, counters, head, new.counters, "__slab_free")); =20 if (likely(!n)) { - if (likely(was_frozen)) { /* * The list lock was not taken therefore no list @@ -3118,7 +3101,7 @@ static void __slab_free(struct kmem_cache *s, struc= t page *page, * Objects left in the slab. If it was not on the partial list before * then add it. */ - if (!kmem_cache_has_cpu_partial(s) && unlikely(!prior)) { + if (unlikely(!prior)) { remove_full(s, n, page); add_partial(n, page, DEACTIVATE_TO_TAIL); stat(s, FREE_ADD_PARTIAL); --=20 2.11.0