From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 A910C3A4F51; Wed, 20 May 2026 09:35:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779269738; cv=none; b=RUhQG8dXPnsMqwiWQ3Wfrm+9q+/H9URlWIvI7k6YZauK1xTao9wEQ0Vubw8L30vQIWlKPRNpivKOfaw8Ku6UTRiuD4Xtfoqc3gzbjMA1gwSb/N//MyTe+Kr7t+SGGgD3pR7Lery6xh9Oe6+2Yj2Tjk8WzRKTZFizZ2/tPWjMAIQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779269738; c=relaxed/simple; bh=gPa4LfxMsVgEEYah2FCalbzmj6BE/lExGX0MWgsjCIk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ihUv6ws4jmO049yyDdaBMf+7MEOFn0X2iO/yKcekASD03eB3UnhDbPzfR904HZ/UQq9S/8Rn8vQJNq0NEf5SSvaArnevm68qTo+zM9UsLOp/42++gFCWKJMDLUQ7eXL3MQAnboU8rKkzB9DHVgZvoLzS3/fKj2P1AcU0ShFhsuc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=GetjQ/uU; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="GetjQ/uU" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A48E41F000E9; Wed, 20 May 2026 09:35:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1779269735; bh=cKQ8TEy4a/F3xgQZDjI4b33O37xBHC3B7sYri3TaWOE=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=GetjQ/uUxGQgtxfzq+bLELhGxJlEL0BVV0+a8LUQgyPJ3AEyqrBND1etreZRkq8ZL 20qfHoY1y4dT1DYsR8cp2k7AGGPczNbv0JeUp12TxGJZKXu6MFRZBU0P02+JUifixp bBaeGTe2q4gxahkVNvRP8alEP+x3AeFii0RE9Jj7Mq2UVfKJujaKIxy255sm7J6tps JeLYFmsmnoolpvXsYYrB09OcH266m9xHJKZUDlUH+gx/CsIlpX2OGd2RTfl46CCnNC WNnoGjWlEd0ZOj7v+FWkDSE2yR52+88zQf+z+jPHaBdYK9vplZwOu9BitMhaww8gTP nmEkJG02q872Q== Message-ID: <4e20f643-6983-4b6e-b12d-c6c4eb20ae0c@kernel.org> Date: Wed, 20 May 2026 18:35:30 +0900 Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 4/4] memcg: multi objcg charge support To: Shakeel Butt , Andrew Morton Cc: Johannes Weiner , Michal Hocko , Roman Gushchin , Muchun Song , Qi Zheng , Alexandre Ghiti , Joshua Hahn , Meta kernel team , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kernel test robot References: <20260520053123.2709959-1-shakeel.butt@linux.dev> <20260520053123.2709959-5-shakeel.butt@linux.dev> Content-Language: en-US From: Harry Yoo In-Reply-To: <20260520053123.2709959-5-shakeel.butt@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 5/20/26 2:31 PM, Shakeel Butt wrote: > Commit 01b9da291c49 ("mm: memcontrol: convert objcg to be per-memcg > per-node type") split a memcg's single obj_cgroup into one per NUMA > node so that reparenting LRU folios can take per-node lru locks. As a > side effect, the per-CPU obj_stock_pcp -- which caches exactly one > cached_objcg -- thrashes on workloads where threads of the same memcg > run on different NUMA nodes. The kernel test robot reported a 67.7% > regression on stress-ng.switch.ops_per_sec from this pattern. > > Mirror the multi-slot pattern already used by memcg_stock_pcp: turn > nr_bytes and cached_objcg into NR_OBJ_STOCK-element arrays, scan all > slots on consume/refill/account, prefer empty slots when inserting, > and evict a random slot only when full. With multiple slots a CPU can > hold the per-node objcg variants of one memcg plus a few siblings > without ever forcing a drain. > > A single int8_t index records which slot the cached slab stats belong > to; the stats are flushed on slot or pgdat change. With NR_OBJ_STOCK > = 5 the layout (verified with pahole) is: > > offset 0 : lock(1) + index(1) + node_id(2) + slab stats(4) = 8B > offset 8 : nr_bytes[5] = 10B > offset 18 : padding = 6B > offset 24 : cached[5] = 40B > offset 64 : (line 2) work_struct + flags (cold) > > so consume_obj_stock, refill_obj_stock and the slab account path each > touch exactly one 64-byte cache line on non-debug 64-bit builds. > > Reported-by: kernel test robot > Closes: https://lore.kernel.org/oe-lkp/202605121641.b6a60cb0-lkp@intel.com > Fixes: 01b9da291c49 ("mm: memcontrol: convert objcg to be per-memcg per-node type") > Signed-off-by: Shakeel Butt > Tested-by: kernel test robot > --- > @@ -3350,19 +3405,45 @@ static void __refill_obj_stock(struct obj_cgroup *objcg, > goto out; > } > > - stock_nr_bytes = stock->nr_bytes; > - if (READ_ONCE(stock->cached_objcg) != objcg) { /* reset if necessary */ > - drain_obj_stock(stock); > + for (i = 0; i < NR_OBJ_STOCK; ++i) { > + struct obj_cgroup *cached = READ_ONCE(stock->cached[i]); > + > + if (!cached) { > + if (empty_slot == -1) > + empty_slot = i; > + continue; > + } > + if (cached == objcg) { > + slot = i; > + break; > + } > + } > + > + if (slot == -1) { > + slot = empty_slot; > + if (slot == -1) { > + slot = get_random_u32_below(NR_OBJ_STOCK); It would break kmalloc_nolock() because _get_random_bytes() uses a spinlock. perhaps prandom_u32_state() should be sufficient in this case. Is there a reason why it uses random eviction, unlike multi-memcg percpu charge cache? Otherwise LGTM! -- Cheers, Harry / Hyeonggon