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[89.27.86.246]) by smtp.gmail.com with ESMTPSA id 38308e7fff4ca-3a63bdbc5dfsm2340611fa.5.2026.09.23.17.14.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 23 Sep 2026 17:14:36 -0700 (PDT) Message-ID: <205181b9-9677-4fcb-873c-732a503fabd9@redhat.com> Date: Thu, 24 Sep 2026 03:14:35 +0300 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 00/12] [PATCH v14 00/12] migrate on fault for device pages To: Jason Gunthorpe , Andrew Morton Cc: linux-mm@kvack.org, dri-devel@lists.freedesktop.org, intel-xe@lists.freedesktop.org, linux-kernel@vger.kernel.org, David Hildenbrand , Leon Romanovsky , Alistair Popple , Balbir Singh , Zi Yan , Matthew Brost , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko References: <20260922053421.4092027-1-mpenttil@redhat.com> <20260922192726.90dec3c4c77b8c9063dbf218@linux-foundation.org> <5b1d0fa6-d183-446e-bc52-56e0afd3f398@redhat.com> <20260923141936.d1f9e5b85355f0bdc6a6ecd2@linux-foundation.org> <20260923232402.GI2545495@nvidia.com> From: =?UTF-8?Q?Mika_Penttil=C3=A4?= In-Reply-To: <20260923232402.GI2545495@nvidia.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: gDKZysi9qDqA22wC2bZmPznYiPgC3OscatwDaerYoaI_1790208878 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 027F3180003 X-Stat-Signature: tonro1mo9d11jmztk85dmock4ptoqqro X-HE-Tag: 1790208882-212353 X-HE-Meta: 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 GHGd/Hx2 bkJTAH6xt7mi8QB9kkjH0yanXA/s6ltWtmnOyrVhZz2ildThZwmhzMlMSphjBWkmjIeGmfO4XR576gbUnqpz2xL7oiY42pQp6s7T9K5wqmO/y2B+FvAFJZGWXLM8rUPjBTCDFIsD/7qvYBx0NHi+d4h4D5fYm5xQgXdDigN64bGls3tfOt6RdaS0xoj3oeD2lPX6iuWo08VSf2GgW5exM24TLgs9TtFZHqwI3MGNcHnC7u3omb2lhv1PRj4g2B6/smoABBLBiQmlP0Y0W5ZVG4AU4DZN+75dUOulDXpAqLg1zL0j5/XIFU8a5v13y6Isryq5UMqVee5ix4vlUUYHAAfujmj5nLFYOqX7MMToL6tnFRL0LuzKCvnLddAG7+4YngKOg1oDpTLALf1kaQxY1c/KMfVvWH7K0Y5oBR2vTs5/mdukvBojALeT+B2o8Rp65TItcEnaUhbESbQjyMFJ+3S+B8FTksfyyvOCwJDfXDqQ5/+Q= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/24/26 02:24, Jason Gunthorpe wrote: > On Wed, Sep 23, 2026 at 02:19:36PM -0700, Andrew Morton wrote: >> On Wed, 23 Sep 2026 08:29:34 +0300 Mika Penttilä wrote: >> >>>>> migration). It is also tricky to code correctly. One page table walk >>>>> could costs over 1000 cpu cycles on X86-64, which is a significant hit. >>>>> >>>>> We should be able to walk the page table once, faulting >>>>> pages in as required and replacing them with migration entries if >>>>> requested. >>>> Sounds sensible. >>>> >>>>> Tested in X86-64 VM with HMM test device, passing the selftests. >>>>> For performance, the migrate throughput tests from the selftests >>>>> show similar numbers (within error margin) as unmodified kernel. >>>> But no performance benefits are demonstrated? >>> There are no performance regressions for current tests. >>> Real benefits come if want to do migrate on fault. >>> For migrate on fault today missing pages are collected as not-present and >>> the caller has to fault them and re-run migrate_vma_setup(); folding >>> HMM_PFN_REQ_FAULT into the collecting walk removes that extra >>> fault+retry round-trip, dropping two page table walks. Page table walks >>> are not cheap. Not to mention simplified implementation for driver. >>> Also, the vma looked up as part of the walk is readily available for >>> migration, eliminating the need for explicit vma lookup - one more >>> performance benefit. Net effect two saved page table walks and >>> one vma lookup. >> It certainly sounds that this series will result in performance >> improvements, but have those improvements been quantified? >> >>> This series also addresses the vanished/reborn page table while >>> collecting problem which can crash current implementation. >> Oh. I didn't get that message from the v14 changelogs, and crashes in >> the current implementation are not what we want. In fact, addressing >> those is more important than speeding things up. > Yeah, what is this about? > > The series still has lots of sashiko remarks, are they legit? Some of them are legit some not. This was actually the first time sashiko managed to apply the series. I will address all the remarks in v15 soon. > > Jason --Mika >