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[2003:cb:c70b:e00:b8a4:8613:1529:1caf]) by smtp.gmail.com with ESMTPSA id o20-20020a5d58d4000000b0031762e89f94sm19173032wrf.117.2023.08.02.08.29.57 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 02 Aug 2023 08:29:58 -0700 (PDT) Message-ID: Date: Wed, 2 Aug 2023 17:29:56 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Subject: Re: [PATCH v2 3/8] kvm: explicitly set FOLL_HONOR_NUMA_FAULT in hva_to_pfn_slow() Content-Language: en-US To: Mel Gorman Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, kvm@vger.kernel.org, linux-kselftest@vger.kernel.org, Andrew Morton , Linus Torvalds , liubo , Peter Xu , Matthew Wilcox , Hugh Dickins , Jason Gunthorpe , John Hubbard , Mel Gorman , Shuah Khan , Paolo Bonzini References: <20230801124844.278698-1-david@redhat.com> <20230801124844.278698-4-david@redhat.com> <20230802152702.wamtroy3zm7nbtvs@techsingularity.net> From: David Hildenbrand Organization: Red Hat In-Reply-To: <20230802152702.wamtroy3zm7nbtvs@techsingularity.net> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On 02.08.23 17:27, Mel Gorman wrote: > On Tue, Aug 01, 2023 at 02:48:39PM +0200, David Hildenbrand wrote: >> KVM is *the* case we know that really wants to honor NUMA hinting falls. >> As we want to stop setting FOLL_HONOR_NUMA_FAULT implicitly, set >> FOLL_HONOR_NUMA_FAULT whenever we might obtain pages on behalf of a VCPU >> to map them into a secondary MMU, and add a comment why. >> >> Do that unconditionally in hva_to_pfn_slow() when calling >> get_user_pages_unlocked(). >> >> kvmppc_book3s_instantiate_page(), hva_to_pfn_fast() and >> gfn_to_page_many_atomic() are similarly used to map pages into a >> secondary MMU. However, FOLL_WRITE and get_user_page_fast_only() always >> implicitly honor NUMA hinting faults -- as documented for >> FOLL_HONOR_NUMA_FAULT -- so we can limit this change to a single location >> for now. >> >> Don't set it in check_user_page_hwpoison(), where we really only want to >> check if the mapped page is HW-poisoned. >> >> We won't set it for other KVM users of get_user_pages()/pin_user_pages() >> * arch/powerpc/kvm/book3s_64_mmu_hv.c: not used to map pages into a >> secondary MMU. >> * arch/powerpc/kvm/e500_mmu.c: only used on shared TLB pages with userspace >> * arch/s390/kvm/*: s390x only supports a single NUMA node either way >> * arch/x86/kvm/svm/sev.c: not used to map pages into a secondary MMU. >> >> This is a preparation for making FOLL_HONOR_NUMA_FAULT no longer >> implicitly be set by get_user_pages() and friends. >> >> Signed-off-by: David Hildenbrand > > Seems sane but I don't know KVM well enough to know if this is the only > relevant case so didn't ack. Makes sense, some careful eyes from KVM people would be appreciated. At least from kvm_main.c POV, I'm pretty confident that that's it. -- Cheers, David / dhildenb