From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-185.mta0.migadu.com (out-185.mta0.migadu.com [91.218.175.185]) (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 9DA2A257435 for ; Wed, 10 Jun 2026 02:48:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.185 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781059688; cv=none; b=EqJoQajHiMeh6rDpVdqfFFJJheTzDtaZei2JdAg6EWmsoki7mV8kP+f/19ljrnkAI2BKOseq4/5LVp2nLtc5/0hpx98GY9iFv8R5hBJaClNeSS1taMsqsUVZjAmQVOWKII+tZuX52SmpgHF9eR5uh5fzgdFNJKISE+ruE5laytE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781059688; c=relaxed/simple; bh=Dp6JSA+LwSgrw3mWKiUPlWENCIn6ICJPcj0VBBjYJyo=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=WiK5qkGJH6+SLX8MrBpM9SKdQEvm1WeJrjKLgSDSZzUn2M8jlxR7Afe01+fI/NjKbb02cOIYm4HATReBgEqL9basos3rg13TCoBj1kt2IJXe3i07XucteNb4x5JWPd17NyQUKL3CMSRdm20k19+1+MEEeetKpkjB/HkRvRUSSC4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=gDf+YFv4; arc=none smtp.client-ip=91.218.175.185 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="gDf+YFv4" Date: Wed, 10 Jun 2026 10:47:54 +0800 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1781059683; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=lkq6AWcrvDXEYK4VWmEuauydPf93rxFze1ELQOyN0Nc=; b=gDf+YFv4ph4C8SIW7GcpK9BNl1xqQWql9vQlsSJRSwoMkBH/wV4qAATBCw/yRT3rQSJH/t lvzs4Jplkq/h5x0b+gaw6vPsQqpzYhu//laoTacJ3AwBJ/sNGrl8S67LS0qE1s9/2vu8Xc rp1rg+nGzKtCCofU1CXmoJNQt15W1Jc= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Hao Li To: "Vlastimil Babka (SUSE)" Cc: Harry Yoo , 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 v2] mm/slub: allocate sheaves on local memory nodes Message-ID: References: <20260601095706.106551-1-hao.li@linux.dev> <33506b25-ab2f-4f31-a380-7c0fe65567a3@kernel.org> <5d8abe93-edd1-4b18-9ea4-7731dc831223@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT On Tue, Jun 09, 2026 at 12:14:55PM +0200, Vlastimil Babka (SUSE) wrote: > On 6/9/26 05:41, Harry Yoo wrote: > > > > > > On 6/3/26 1:26 PM, Hao Li wrote: > >> On Mon, Jun 01, 2026 at 08:28:16PM +0900, Harry Yoo wrote: > >>> On 6/1/26 6:56 PM, Hao Li wrote: > >>>> Sheaf structs are exchanged through node-local barns. Since barn structs > >>>> are already allocated from their local NUMA node, this patch aims to > >>>> allocate sheaf structs from their local memory nodes as well. > >>>> > >>>> To achieve this, the obvious choice would be using cpu_to_mem(). > >>>> However, init_percpu_sheaves() and bootstrap_cache_sheaves() iterate > >>>> through possible CPUs, whereas cpu_to_mem() is only initialized for > >>>> online CPUs. Therefore, we cannot use cpu_to_mem() and instead need to > >>>> use local_memory_node(cpu_to_node(cpu)), similar to what > >>>> __build_all_zonelists() does. > >>>> > >>>> The primary goal of this patch is to improve NUMA node locality. > >>>> Although the actual performance impact is minor, it still yields a ~1% > >>>> improvement on a 192-core, 8-NUMA-node system when testing with the > >>>> will-it-scale mmap test case. > >>> > >>> Oh, nice :) > >>> > >>> I have a question though... > >>> > >>> I wonder if would be better to handle this by e.g.) not returning empty > >>> sheaves back to barn and freeing them if the node id doesn't match and > >>> it's not a memoryless node. > >>> > >>> init_percpu_sheaves() and bootstrap_cache_sheaves() are not the only > >>> places that can allocate sheaves from remote nodes; sheaves allocation > >>> could fall back to other nodes and then SLUB could keep reusing those > >>> sheaves from remote nodes even after memory is reclaimed. > >> > >> This is a good catch. In addition to the fallback mechanism, task migration > >> between CPUs in __pcs_replace_empty_main() and __pcs_replace_full_main() can > >> also mix up sheaf structs across different barns. So yeah, changing allocation > >> locality is not a silver bullet. > >> > >>> If this works well, we probably don't need to handle it in > >>> init_percpu_sheaves() and bootstrap_cache_sheaves() at all as they will > >>> eventually be freed, while covering the other case too? > >> > >> freeing the empty sheaf if the NUMA node mismatches instead of putting it back > >> into the barn is indeed a good idea. I like it. But unfortunately, my testing > >> didn't show a clear performance improvement, though there was no noticeable > >> degradation either. :-( > > > > Hmm... the idea still makes sense to me, but yeah, it's not late to fix > > it when we have data to back up. > > I think if that approach doesn't complicate things unreasonably, it makes > sense to do it even if there are no clear wins (as long as there are no > regressions). This make sense to me. let me double check the performance impact. Thanks! -- Thanks, Hao