From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id CD1E2CD98FC for ; Wed, 11 Oct 2023 08:05:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230111AbjJKIFu (ORCPT ); Wed, 11 Oct 2023 04:05:50 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38726 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229879AbjJKIFs (ORCPT ); Wed, 11 Oct 2023 04:05:48 -0400 Received: from szxga03-in.huawei.com (szxga03-in.huawei.com [45.249.212.189]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5B3E092 for ; Wed, 11 Oct 2023 01:05:46 -0700 (PDT) Received: from dggpemm100001.china.huawei.com (unknown [172.30.72.55]) by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4S54wp0xLGzkYC2; Wed, 11 Oct 2023 16:01:46 +0800 (CST) Received: from [10.174.177.243] (10.174.177.243) by dggpemm100001.china.huawei.com (7.185.36.93) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.31; Wed, 11 Oct 2023 16:05:43 +0800 Message-ID: Date: Wed, 11 Oct 2023 16:05:42 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH -next 1/7] mm_types: add _last_cpupid into folio Content-Language: en-US To: "Huang, Ying" , Matthew Wilcox CC: Andrew Morton , , , , Zi Yan , Mel Gorman References: <20231010064544.4162286-1-wangkefeng.wang@huawei.com> <20231010064544.4162286-2-wangkefeng.wang@huawei.com> <3b56b26b-a550-4e06-b355-55564b40cfb5@huawei.com> <874jixhfeu.fsf@yhuang6-desk2.ccr.corp.intel.com> From: Kefeng Wang In-Reply-To: <874jixhfeu.fsf@yhuang6-desk2.ccr.corp.intel.com> Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [10.174.177.243] X-ClientProxiedBy: dggems702-chm.china.huawei.com (10.3.19.179) To dggpemm100001.china.huawei.com (7.185.36.93) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2023/10/11 13:55, Huang, Ying wrote: > Kefeng Wang writes: > >> On 2023/10/10 20:33, Matthew Wilcox wrote: >>> On Tue, Oct 10, 2023 at 02:45:38PM +0800, Kefeng Wang wrote: >>>> At present, only arc/sparc/m68k define WANT_PAGE_VIRTUAL, both of >>>> them don't support numa balancing, and the page struct is aligned >>>> to _struct_page_alignment, it is safe to move _last_cpupid before >>>> 'virtual' in page, meanwhile, add it into folio, which make us to >>>> use folio->_last_cpupid directly. >>> What do you mean by "safe"? I think you mean "Does not increase the >>> size of struct page", but if that is what you mean, why not just say so? >>> If there's something else you mean, please explain. >> >> Don't increase size of struct page and don't impact the real order of >> struct page as the above three archs without numa balancing support. >> >>> In any event, I'd like to see some reasoning that _last_cpupid is >>> actually >>> information which is logically maintained on a per-allocation basis, >>> not a per-page basis (I think this is true, but I honestly don't know) >> >> The _last_cpupid is updated in should_numa_migrate_memory() from numa >> fault(do_numa_page, and do_huge_pmd_numa_page), it is per-page(normal >> page and PMD-mapped page). Maybe I misunderstand your mean, please >> correct me. > > Because PTE mapped THP will not be migrated according to comments and > folio_test_large() test in do_numa_page(). Only _last_cpuid of the head > page will be used (that is, on per-allocation basis). Although in > change_pte_range() in mprotect.c, _last_cpuid of tail pages may be > changed, they are not used actually. All in all, _last_cpuid is on > per-allocation basis for now. Thanks for clarification, yes, it's what I mean, too > > In the future, it's hard to say. PTE-mapped THPs or large folios give > us an opportunity to check whether the different parts of a folio are > accessed by multiple sockets, so that we should split the folio. But > this is just some possibility in the future. It depends on memory access behavior of application,if multiple sockets access a large folio/PTE-mappped THP frequently, split maybe better, or it is enough to just migrate the entire folio. > > -- > Best Regards, > Huang, Ying >