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[2003:cb:c705:4200:ce79:acf6:d832:60df]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3825491103fsm2483483f8f.55.2024.11.20.08.44.03 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 20 Nov 2024 08:44:04 -0800 (PST) Message-ID: Date: Wed, 20 Nov 2024 17:44:03 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 0/4] KVM: ioctl for populating guest_memfd From: David Hildenbrand To: kalyazin@amazon.com, pbonzini@redhat.com, corbet@lwn.net, kvm@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org Cc: jthoughton@google.com, brijesh.singh@amd.com, michael.roth@amd.com, graf@amazon.de, jgowans@amazon.com, roypat@amazon.co.uk, derekmn@amazon.com, nsaenz@amazon.es, xmarcalx@amazon.com, Sean Christopherson , linux-mm@kvack.org References: <20241024095429.54052-1-kalyazin@amazon.com> <08aeaf6e-dc89-413a-86a6-b9772c9b2faf@amazon.com> <01b0a528-bec0-41d7-80f6-8afe213bd56b@redhat.com> <55b6b3ec-eaa8-494b-9bc7-741fe0c3bc63@amazon.com> <9286da7a-9923-4a3b-a769-590e8824fa10@redhat.com> Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam10 X-Stat-Signature: d7n8ubrmneu9msmzd4rtuqzn55pw71m1 X-Rspamd-Queue-Id: B52EE80004 X-Rspam-User: X-HE-Tag: 1732120951-644261 X-HE-Meta: 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 rn4L2i+P PYtkJgEKd3rOmcNzuJzkdckxsGjRCjYtvOvH/+4ij/NEoKfQ60SvaEB0RwzVzSQkg516Mn4agkA9gVFzOZV72R0fy0yrocGYNle2pfV9ZPCG92B086/M99oD+Xw6djpFhheAy4M9S4zx3Y3ZZoWNhrjjHDrGPAgHJGCf4oMw3lMHRi2U7eUQQoCS5Iv/YkWv1nuGTERyD2sXwpagdYQGtV8TSI0RVaqUGJWz/kLbxEaJPelSIJkgcNNwrRE7YWWCCcdGzL8piYrGfmzMmzk1k+cdyoPdiyHEP+y1788Mj2Z5WqF+QCJHoJe4NmVmYeGG8AJQNOsP1vXPgynAP8feBW/4zoshyFe8B358pGgtOJvxRJkBaX20Q3zYnacfisOC5EPQ7oQWACPAeg49T37xl8fLJhy1yxAcV/Ujd8zQ+y+MGssy2gvOiY9xzS6U52XlHPExv X-Bogosity: Ham, tests=bogofilter, spamicity=0.000005, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: >> No, I can't immediately see why it shouldn't work. My main concern >> would probably still be about the latency of the population stage as I >> can't see why it would improve compared to what we have now, because my > > feeling is this is linked with the sharedness property of guest_memfd. > > If the problem is the "pagecache" overhead, then yes, it will be a > harder nut to crack. But maybe there are some low-hanging fruits to > optimize? Finding the main cause for the added overhead would be > interesting. Can you compare uffdio_copy() when using anonymous memory vs. shmem? That's likely the best we could currently achieve with guest_memfd. There is the tools/testing/selftests/mm/uffd-stress benchmark, not sure if that is of any help; it SEGFAULTS for me right now with a (likely) division by 0. -- Cheers, David / dhildenb