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 VHs5PiO2 dRoFrdtzo+stH3yt2b8ODpBz0D8sGWONbd1BH4A3hHOrDPOMGZTvmin0Xpy/2jr9Lwiyk81y03QHBMhIwk8jOFZwVwfnV1Sts9OCmopvyFYXj1qCEtbRJBj75eXkaT4mV3e/JlGY5bw6tlLzG4BodCy07uw7LUtsNXGrQe6cYCj1nmvCcyPx5eZGIFaxwP9FctBc5My3i6qwulG16HkIy4hTG1FN7cIZM6S2C+y5XWmMaswObBU/FRZyaXWhuBbPOeJf7tESKSFkkjEutkwzMEiL68dQVZJrT4VxmghoXFuJjgQtM120QCUz8o1qiEHuJPCPKC19OvBfZeX3L76G3OxozOAehKH+FdlGEE/9w8ZjYvZrJMbtk1/td+Ocs5ygUTmZGkp6/nXx3rr7S7uTwLwwvlyPtug9BUmq49eftrBGO2wBxMwJLskufHG9hfrG39uMBCDWJv6V91cVKrjwrjhoeEzsrU7+93hPb1MUprvz3UwiXCWbnFt63SVMSGWbj9mSvbmo9p7awkii7LzIbe8+TNA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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? Jason