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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1780026717; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Vm7EtoPN4QmeJ2Y9CSRukPyMKuVmFRo7olYJHuJ3ke8=; b=A1u8pdDoeRJKed4RmTVAxkvXMMDzLTT/u2icwQoTkOfKw/eCkU3sFNbZX7SpzsB87+/cXP nb6dKS9jiBAGo4D+oZa3/Onc+9Jasal9zy9SEOOOWlM0YH/ub3HuI1Ygi8vyB1zXrDhPKu ZdTJrfVlgbXNEjJ97gzG3LXZNK/w9co= From: Hao Li To: vbabka@kernel.org, harry@kernel.org, akpm@linux-foundation.org Cc: cl@gentwo.org, rientjes@google.com, roman.gushchin@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hao Li Subject: [PATCH v3 2/2] mm/slub: detach and reattach partial slabs in batch Date: Fri, 29 May 2026 11:50:52 +0800 Message-ID: <20260529035120.81304-3-hao.li@linux.dev> In-Reply-To: <20260529035120.81304-1-hao.li@linux.dev> References: <20260529035120.81304-1-hao.li@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Queue-Id: DBDA518000B X-Rspamd-Server: rspam03 X-Stat-Signature: dqc3h1pgmabxonbgzhwsgtky433hn3dr X-HE-Tag: 1780026719-417058 X-HE-Meta: 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 rXvWQc6+ HEvSMLqsSXpsr30xF/MoG46HRbQ74wv1JOy8n1oU+mSH6mfAEpz2O0OVjyhQecqSOk96X8YkUd0GAaB6bK6aOdiLBFSHuAlUBmwSGGeIVjLFOau3A/PTw1xio8gFwh6gruAHU8aEnM02bUPoqGLfs8v8kn/bFCjocyzlm1XreDpX4a5Pv/6HSwCAbrViPtOrkpuCV Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: get_partial_node_bulk() moves each selected slab from the node's partial list to the local pc->slabs list using a remove_partial() and list_add() pair. In practice, the loop often detaches several adjacent slabs. Doing this individually repeatedly manipulates list pointers while holding n->list_lock, which causes unnecessary churn. To demonstrate this, the counts below show how often single vs. multiple consecutive slabs are retrieved during a will-it-scale mmap stress test: consecutive_slabs_count frequency = 1 277345324 = 2 335238023 = 3 175717884 >= 4 88862337 The data confirms that retrieving multiple contiguous slabs is highly frequent. To optimize this, track contiguous runs of matching slabs and move each run in a single operation using list_bulk_move_tail(). This reduces list pointer churn inside the lock critical section. Apply the same optimization to __refill_objects_node() when reattaching leftover partial slabs back to the node's partial list. The will-it-scale mmap benchmark shows a 2% ~ 5% performance improvement after applying this patch. Signed-off-by: Hao Li --- mm/slub.c | 28 ++++++++++++++++++++-------- 1 file changed, 20 insertions(+), 8 deletions(-) diff --git a/mm/slub.c b/mm/slub.c index 45aa0a834f97..4fdf5c36a69b 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -3751,6 +3751,7 @@ static bool get_partial_node_bulk(struct kmem_cache *s, bool allow_spin) { struct slab *slab, *slab2; + struct slab *first = NULL, *last = NULL; unsigned int total_free = 0; unsigned long flags; @@ -3769,8 +3770,15 @@ static bool get_partial_node_bulk(struct kmem_cache *s, struct freelist_counters flc; unsigned int slab_free; - if (!pfmemalloc_match(slab, pc->flags)) + if (!pfmemalloc_match(slab, pc->flags)) { + if (first) { + list_bulk_move_tail(&pc->slabs, + &first->slab_list, + &last->slab_list); + first = NULL; + } continue; + } /* * determine the number of free objects in the slab racily @@ -3787,15 +3795,20 @@ static bool get_partial_node_bulk(struct kmem_cache *s, && total_free + slab_free > pc->max_objects) break; - remove_partial(n, slab); - - list_add(&slab->slab_list, &pc->slabs); + if (!first) + first = slab; + last = slab; + clear_node_partial_state(n, slab); total_free += slab_free; if (total_free >= pc->max_objects) break; } + if (first) + list_bulk_move_tail(&pc->slabs, &first->slab_list, + &last->slab_list); + spin_unlock_irqrestore(&n->list_lock, flags); return total_free > 0; } @@ -7206,11 +7219,10 @@ __refill_objects_node(struct kmem_cache *s, void **p, gfp_t gfp, unsigned int mi if (!list_empty(&pc.slabs)) { spin_lock_irqsave(&n->list_lock, flags); - list_for_each_entry_safe(slab, slab2, &pc.slabs, slab_list) { + list_for_each_entry(slab, &pc.slabs, slab_list) + set_node_partial_state(n, slab); - list_del(&slab->slab_list); - add_partial(n, slab, ADD_TO_TAIL); - } + list_splice_tail(&pc.slabs, &n->partial); spin_unlock_irqrestore(&n->list_lock, flags); } -- 2.54.0