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([2a09:80c0:192:0:5dac:bf3d:c41:c3e7]) by smtp.gmail.com with ESMTPSA id z10-20020a5d4d0a000000b0031ad5a54bedsm1686403wrt.9.2023.08.17.00.38.38 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 17 Aug 2023 00:38:38 -0700 (PDT) Message-ID: <5c9e52ab-d46a-c939-b48f-744b9875ce95@redhat.com> Date: Thu, 17 Aug 2023 09:38:37 +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: [RFC PATCH v2 0/5] Reduce NUMA balance caused TLB-shootdowns in a VM To: Yan Zhao , John Hubbard Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, pbonzini@redhat.com, seanjc@google.com, mike.kravetz@oracle.com, apopple@nvidia.com, jgg@nvidia.com, rppt@kernel.org, akpm@linux-foundation.org, kevin.tian@intel.com, Mel Gorman , alex.williamson@redhat.com References: <6b48a161-257b-a02b-c483-87c04b655635@redhat.com> <1ad2c33d-95e1-49ec-acd2-ac02b506974e@nvidia.com> <846e9117-1f79-a5e0-1b14-3dba91ab8033@redhat.com> <4271b91c-90b7-4b48-b761-b4535b2ae9b7@nvidia.com> <37325c27-223d-400d-bd86-34bdbfb92a5f@nvidia.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 6BD2540012 X-Stat-Signature: xo5tonmi5zft7ybj7d5u5i3nkoiar56k X-HE-Tag: 1692257925-547343 X-HE-Meta: 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 VpbP8GBA QRw1drhtZFrC3MgcnPtl8kfzu7y1fE8uF/+ZsIesw5yyU5dv9CyoCsW4VUaoGM3l3UAmRY3F99gXF2PUvHdoWpXvMuZ1zIKtGNT7Rauy0/Uhyp+PG+02RQ6ljuW4P59Dee1pebamkC7zV+vhCxccPPmUS+3BfaeOJiUVpB3+uJnbW+LWHPFtCMdpRQFuvcm+E2xSpB9UXHRhY1EeYoF5DUmULOztD/U3TcbYnorOfx2Cdnk6StL5tXxylatE1lssP+nQGV6lFWa9nxnGAgyF1xEtOYuAOiXRt+OSpN/s/J/NoMuKVcnAvgjT9vRHJAdPuZqiGhozBOwIsvv4shnnl/+iWF+ytqTh8QDo6oC4NLtgbE5zdHkOMC01iPop6sc6Hpjo/UDpil03WDbhX+xwaWPKgmr3jIlXc836p X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 17.08.23 07:05, Yan Zhao wrote: > On Wed, Aug 16, 2023 at 11:00:36AM -0700, John Hubbard wrote: >> On 8/16/23 02:49, David Hildenbrand wrote: >>> But do 32bit architectures even care about NUMA hinting? If not, just >>> ignore them ... >> >> Probably not! >> >> ... >>>> So, do you mean that let kernel provide a per-VMA allow/disallow >>>> mechanism, and >>>> it's up to the user space to choose between per-VMA and complex way or >>>> global and simpler way? >>> >>> QEMU could do either way. The question would be if a per-vma settings >>> makes sense for NUMA hinting. >> >> From our experience with compute on GPUs, a per-mm setting would suffice. >> No need to go all the way to VMA granularity. >> > After an offline internal discussion, we think a per-mm setting is also > enough for device passthrough in VMs. > > BTW, if we want a per-VMA flag, compared to VM_NO_NUMA_BALANCING, do you > think it's of any value to providing a flag like VM_MAYDMA? > Auto NUMA balancing or other components can decide how to use it by > themselves. Short-lived DMA is not really the problem. The problem is long-term pinning. There was a discussion about letting user space similarly hint that long-term pinning might/will happen. Because when long-term pinning a page we have to make sure to migrate it off of ZONE_MOVABLE / MIGRATE_CMA. But the kernel prefers to place pages there. So with vfio in QEMU, we might preallocate memory for the guest and place it on ZONE_MOVABLE/MIGRATE_CMA, just so long-term pinning has to migrate all these fresh pages out of these areas again. So letting the kernel know about that in this context might also help. -- Cheers, David / dhildenb