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 E9B48C4332F for ; Tue, 31 Oct 2023 11:56:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235931AbjJaL4o (ORCPT ); Tue, 31 Oct 2023 07:56:44 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36446 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236211AbjJaL4Y (ORCPT ); Tue, 31 Oct 2023 07:56:24 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 1A41510E5 for ; Tue, 31 Oct 2023 04:55:56 -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 D76BEC15; Tue, 31 Oct 2023 04:56:36 -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 C4E713F64C; Tue, 31 Oct 2023 04:55:52 -0700 (PDT) Message-ID: Date: Tue, 31 Oct 2023 11:55:51 +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 From: Ryan Roberts 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> In-Reply-To: <7a3a2d49-528d-4297-ae19-56aa9e6c59c6@arm.com> 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 11:50, 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, > > 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). > > 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? > > 2) The global control will continue to drive the file-backed memory decision > (for now), even when hugepages-2048kB/enabled != "global"; agreed? > > Thanks, > Ryan > Also, an implementation question: hugepage_vma_check() doesn't currently care whether enabled="never" for DAX VMAs (although it does honour MADV_NOHUGEPAGE and the prctl); It will return true regardless. Is that by design? It couldn't fathom any reasoning from the commit log: bool hugepage_vma_check(struct vm_area_struct *vma, unsigned long vm_flags, bool smaps, bool in_pf, bool enforce_sysfs) { if (!vma->vm_mm) /* vdso */ return false; /* * Explicitly disabled through madvise or prctl, or some * architectures may disable THP for some mappings, for * example, s390 kvm. * */ if ((vm_flags & VM_NOHUGEPAGE) || test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags)) return false; /* * If the hardware/firmware marked hugepage support disabled. */ if (transparent_hugepage_flags & (1 << TRANSPARENT_HUGEPAGE_UNSUPPORTED)) return false; /* khugepaged doesn't collapse DAX vma, but page fault is fine. */ if (vma_is_dax(vma)) return in_pf; <<<<<<<< ... }