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 97E07C4332F for ; Tue, 31 Oct 2023 13:12:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344457AbjJaNM1 (ORCPT ); Tue, 31 Oct 2023 09:12:27 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57448 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1344447AbjJaNMZ (ORCPT ); Tue, 31 Oct 2023 09:12:25 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 365F9E4 for ; Tue, 31 Oct 2023 06:12:22 -0700 (PDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 94DFCC15; Tue, 31 Oct 2023 06:13:03 -0700 (PDT) Received: from [10.1.34.180] (XHFQ2J9959.cambridge.arm.com [10.1.34.180]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 82A713F738; Tue, 31 Oct 2023 06:12:19 -0700 (PDT) Message-ID: Date: Tue, 31 Oct 2023 13:12:18 +0000 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 0/9] variable-order, large folios for anonymous memory Content-Language: en-GB To: David Hildenbrand , Andrew Morton , Matthew Wilcox , Yin Fengwei , Yu Zhao , Catalin Marinas , Anshuman Khandual , Yang Shi , "Huang, Ying" , Zi Yan , Luis Chamberlain , Itaru Kitayama , "Kirill A. Shutemov" , John Hubbard , David Rientjes , Vlastimil Babka , Hugh Dickins Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org References: <20230929114421.3761121-1-ryan.roberts@arm.com> <6d89fdc9-ef55-d44e-bf12-fafff318aef8@redhat.com> <7a3a2d49-528d-4297-ae19-56aa9e6c59c6@arm.com> From: Ryan Roberts In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 31/10/2023 11:58, David Hildenbrand wrote: > On 31.10.23 12:50, Ryan Roberts wrote: >> On 06/10/2023 21:06, David Hildenbrand wrote: >> [...] >>> >>> Change 2: sysfs interface. >>> >>> If we call it THP, it shall go under "/sys/kernel/mm/transparent_hugepage/", I >>> agree. >>> >>> What we expose there and how, is TBD. Again, not a friend of "orders" and >>> bitmaps at all. We can do better if we want to go down that path. >>> >>> Maybe we should take a look at hugetlb, and how they added support for multiple >>> sizes. What *might* make sense could be (depending on which values we actually >>> support!) >>> >>> >>> /sys/kernel/mm/transparent_hugepage/hugepages-64kB/ >>> /sys/kernel/mm/transparent_hugepage/hugepages-128kB/ >>> /sys/kernel/mm/transparent_hugepage/hugepages-256kB/ >>> /sys/kernel/mm/transparent_hugepage/hugepages-512kB/ >>> /sys/kernel/mm/transparent_hugepage/hugepages-1024kB/ >>> /sys/kernel/mm/transparent_hugepage/hugepages-2048kB/ >>> >>> Each one would contain an "enabled" and "defrag" file. We want something minimal >>> first? Start with the "enabled" option. >>> >>> >>> enabled: always [global] madvise never >>> >>> Initially, we would set it for PMD-sized THP to "global" and for everything else >>> to "never". >> >> Hi David, > > Hi! > >> >> I've just started coding this, and it occurs to me that I might need a small >> clarification here; the existing global "enabled" control is used to drive >> decisions for both anonymous memory and (non-shmem) file-backed memory. But the >> proposed new per-size "enabled" is implicitly only controlling anon memory (for >> now). > > Anon was (way) first, and pagecache later decided to reuse that one as an > indication whether larger folios are desired. > > For the pagecache, it's just a way to enable/disable it globally. As there is no > memory waste, nobody currently really cares about the exact sized the pagecache > is allocating (maybe that will change at some point, maybe not, who knows). Yup. Its not _just_ about allocation though; its also about collapse (MADV_COLLAPSE, khugepaged) which is supported for pagecache pages. I can imagine value in collapsing to various sizes that are beneficial for HW... anyway that's for another day. > >> >> 1) Is this potentially confusing for the user? Should we rename the per-size >> controls to "anon_enabled"? Or is it preferable to jsut keep it vague for now so >> we can reuse the same control for file-backed memory in future? > > The latter would be my take. Just like we did with the global toggle. ACK > >> >> 2) The global control will continue to drive the file-backed memory decision >> (for now), even when hugepages-2048kB/enabled != "global"; agreed? > > That would be my take; it will allocate other sizes already, so just glue it to > the global toggle and document for the other toggles that they only control > anonymous THP for now. ACK >