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From: Hao Li To: Harry Yoo Cc: vbabka@kernel.org, akpm@linux-foundation.org, cl@gentwo.org, rientjes@google.com, roman.gushchin@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/slub: batch-detach node partial slabs Message-ID: References: <20260525032233.10847-1-hao.li@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Queue-Id: AACA11C000C X-Stat-Signature: 4qgc8ptswqdmnjir3djs6u8eq7ow5qyn X-Rspamd-Server: rspam06 X-HE-Tag: 1779786563-115203 X-HE-Meta: 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 GMOfJfL6 0Ez7w77LlUDLGklGua6z9cTIMK3nlmKVWaue/j5e+WF68uaGWu87qKPgPlbX5VWlqtKNhJt+VJCr8h3cVAoBvIYvuk0oAxYn2xnQJTizdmXVFgh+FkWRmk2ezEpIAFutSOsBiRVWhpsZ96M+erdh6f5Txvt/mjFzBFiq5FRM1K1gvaOgYvWlmj9uRcAMxi136Evvai6jShjY7aP4= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, May 26, 2026 at 04:37:46PM +0900, Harry Yoo wrote: > > > On 5/25/26 12:22 PM, Hao Li wrote: > > get_partial_node_bulk() used to move each selected slab from the node > > 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, so this repeatedly manipulates list pointers while holding > > n->list_lock, which causes unnecessary churn. > > > > Instead, track contiguous runs of matching slabs and move each run with > > list_bulk_move_tail() in one operation. > > TIL list_bulk_move_tail() :D I had to dig through list.h for ages just to find it :P > > > This reduces list pointer churn> inside the lock critical section. > > Similar to this, can we return all slabs in pc->slabs at once when returning > those slabs to the list? ... I see Vlastimil removed 'nr of empty slabs' > check in the other series already. > > Now that it inserts slabs to the tail with Vlastimil's patchset, let's do a > list_splice_tail() instead? Great idea! then both get and put operations will be highly efficient. > > > The mmap2 testcase shows a 5% improvement after applying this patch. > > > > Signed-off-by: Hao Li > > --- > > mm/slub.c | 22 ++++++++++++++++++---- > > 1 file changed, 18 insertions(+), 4 deletions(-) > > > > diff --git a/mm/slub.c b/mm/slub.c > > index 04692a6f9128..180973a4a3d2 100644 > > --- a/mm/slub.c > > +++ b/mm/slub.c > > @@ -3775,15 +3783,21 @@ 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; > > > + slab_clear_node_partial(slab); > > + n->nr_partial--; > > Perhaps factor out those two statements into to a common function and call > it in get_partial_node_bulk() and remove_partial()? Agreed, this is very reasonable. > > 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; > > } > Thanks for the review! -- Thanks, Hao