From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5981B399351 for ; Mon, 16 Mar 2026 13:33:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773668036; cv=none; b=t4KUg9m70gPG9bSF/ZL/YB9dSLx+eEfu79U9lOHjJ3Tiwlmvdm8klIq5WG2zcaonBc0ddJR3c4Cup5VrEq5ZBve9WJvG93y2GXwWoswWH26e0y60mc+zB0Mi5nvvSl2BFo8mZBRERqIseBRZmczsNabiottpQcf9f55w4apPWAc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773668036; c=relaxed/simple; bh=LYoMYbkubw56J1IU4QmmSj6p+2qVdbBFc92Lq0WLyIk=; h=Message-ID:Date:MIME-Version:From:Subject:To:Cc:References: In-Reply-To:Content-Type; b=d+ihNytBCOVbrxiIS9dbVwNDu9SJfP8yCqN8vyMriqNjOAFC1NrhZycegU4QVVWWk/Xo3EAEh4Ih9YMTBqGmllp/1OUyYSeM1n304UwXXiqBy3cTQbKDURJQ5xSzcevYOdl7H+wHHssVxCrzHYAIVPJizbfw0TYKyJ6VJWv9VFA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=bwaxByRQ; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="bwaxByRQ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 376EFC19421; Mon, 16 Mar 2026 13:33:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773668036; bh=LYoMYbkubw56J1IU4QmmSj6p+2qVdbBFc92Lq0WLyIk=; h=Date:From:Subject:To:Cc:References:In-Reply-To:From; b=bwaxByRQGj/YvaemSLfVHRUCMGiimGB/69S4PEpq5+xefFKADjoL7I3Ww/5/IbFG/ I2MRAo4AhlOmCCFoO5JpHAVShgWciywQwlzLi7ehDzS2fo3flmh8H1glREBxdiI/oV OhGc/acsvcR+JnQJ+81Ix7bcip7bYpyMwLq1jU1shlkSG73COwfE76NkQ++oFJTVxr gOM0RtlDUR/MmvrFufTb1uJ005b2LAEdzTfeE+rhkXptVJLFH6lqIeL67I41Ralc1O wUhoHKroWAz/xD37TZ8UKKaH6XmlwJDtLCfXLI/oMHOfUwKHsI5Ybd6glHjlEOCkiP gGKepnrp/Z6Rg== Message-ID: Date: Mon, 16 Mar 2026 14:33:52 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird From: "Vlastimil Babka (SUSE)" Subject: Re: [PATCH 0/3] slab: support memoryless nodes with sheaves Content-Language: en-US To: Ming Lei , Harry Yoo Cc: Hao Li , Andrew Morton , Christoph Lameter , David Rientjes , Roman Gushchin , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260311-b4-slab-memoryless-barns-v1-0-70ab850be4ce@kernel.org> In-Reply-To: <20260311-b4-slab-memoryless-barns-v1-0-70ab850be4ce@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 3/11/26 09:25, Vlastimil Babka (SUSE) wrote: > This is the draft patch from [1] turned into a proper series with > incremental changes. It's based on v7.0-rc3. It's too intrusive for a > 7.0 hotfix, so we'll only be able to fix/reduce the regression in 7.1. I > hope it's acceptable given it's a non-standard configuration, 7.0 is not > a LTS, and it's a perf regression, not functionality. > > Ming can you please retest this on top of v7.0-rc3, which already has > fb1091febd66 ("mm/slab: allow sheaf refill if blocking is not > allowed"). Separate data point for v7.0-rc3 could be also useful. > > [1] https://lore.kernel.org/all/c6a01f7e-c6eb-454b-9b9e-734526dd659d@kernel.org/ > > Signed-off-by: Vlastimil Babka (SUSE) > --- > Vlastimil Babka (SUSE) (3): > slab: decouple pointer to barn from kmem_cache_node > slab: create barns for online memoryless nodes > slab: free remote objects to sheaves on memoryless nodes > > mm/slab.h | 7 +- > mm/slub.c | 256 +++++++++++++++++++++++++++++++++++++++++++++----------------- > 2 files changed, 191 insertions(+), 72 deletions(-) > --- > base-commit: 1f318b96cc84d7c2ab792fcc0bfd42a7ca890681 > change-id: 20260311-b4-slab-memoryless-barns-fad64172ba05 > > Best regards, Range-diff in slab/for-7.1/sheaves after applying Harry's feedback: 2: cc67056e94f1 ! 472: b002755da434 slab: decouple pointer to barn from kmem_cache_node @@ Commit message Link: https://patch.msgid.link/20260311-b4-slab-memoryless-barns-v1-1-70ab850be4ce@kernel.org Signed-off-by: Vlastimil Babka (SUSE) + Reviewed-by: Harry Yoo ## mm/slab.h ## @@ mm/slab.h: struct kmem_cache_order_objects { @@ mm/slub.c: struct kmem_cache_node { /* - * Get the barn of the current cpu's closest memory node. It may not exist on - * systems with memoryless nodes but without CONFIG_HAVE_MEMORYLESS_NODES -+ * Get the barn of the current cpu's memory node. It may be a memoryless node. ++ * Get the barn of the current cpu's NUMA node. It may be a memoryless node. */ static inline struct node_barn *get_barn(struct kmem_cache *s) { @@ mm/slub.c: struct kmem_cache_node { - return NULL; - - return n->barn; -+ return get_barn_node(s, numa_node_id()); ++ return get_barn_node(s, numa_mem_id()); } /* 3: 285bca63cf15 ! 473: f811cc3d9f6e slab: create barns for online memoryless nodes @@ Commit message nodes, tracked in a new nodemask slab_barn_nodes. Also add a cpu hotplug callback as that's when a memoryless node can become online. - Change rcu_sheaf->node assignment to numa_node_id() so it's returned to - the barn of the local cpu's (potentially memoryless) node, and not to - the nearest node with memory anymore. + Change both get_barn() and rcu_sheaf->node assignment to numa_node_id() + so it's returned to the barn of the local cpu's (potentially memoryless) + node, and not to the nearest node with memory anymore. + + On systems with CONFIG_HAVE_MEMORYLESS_NODES=y (which are not the main + target of this change) barns did not exist on memoryless nodes, but + get_barn() using numa_mem_id() meant a barn was returned from the + nearest node with memory. This works, but the barn lock contention + increases with every such memoryless node. With this change, barn will + be allocated also on the memoryless node, reducing this contention in + exchange for increased memory consumption. Reported-by: Ming Lei Link: https://lore.kernel.org/all/aZ0SbIqaIkwoW2mB@fedora/ [1] Link: https://patch.msgid.link/20260311-b4-slab-memoryless-barns-v1-2-70ab850be4ce@kernel.org Signed-off-by: Vlastimil Babka (SUSE) + Reviewed-by: Harry Yoo ## mm/slub.c ## +@@ mm/slub.c: static inline struct node_barn *get_barn_node(struct kmem_cache *s, int node) + */ + static inline struct node_barn *get_barn(struct kmem_cache *s) + { +- return get_barn_node(s, numa_mem_id()); ++ return get_barn_node(s, numa_node_id()); + } + + /* @@ mm/slub.c: static inline struct node_barn *get_barn(struct kmem_cache *s) */ static nodemask_t slab_nodes; 4: 1fe49af3aa46 ! 474: 86e18f36844f slab: free remote objects to sheaves on memoryless nodes @@ Commit message Link: https://patch.msgid.link/20260311-b4-slab-memoryless-barns-v1-3-70ab850be4ce@kernel.org Signed-off-by: Vlastimil Babka (SUSE) + Reviewed-by: Harry Yoo ## mm/slub.c ## @@ mm/slub.c: bool __kfree_rcu_sheaf(struct kmem_cache *s, void *obj)