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Message-ID: <90aca1e9-61b5-88d-d28c-369e6973559e@google.com> Date: Sun, 7 Feb 2021 18:18:01 -0800 (PST) From: David Rientjes <rientjes@...gle.com> To: "Song Bao Hua (Barry Song)" <song.bao.hua@...ilicon.com> cc: Matthew Wilcox <willy@...radead.org>, "Wangzhou (B)" <wangzhou1@...ilicon.com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>, "linux-mm@...ck.org" <linux-mm@...ck.org>, "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, "linux-api@...r.kernel.org" <linux-api@...r.kernel.org>, Andrew Morton <akpm@...ux-foundation.org>, Alexander Viro <viro@...iv.linux.org.uk>, "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>, "jgg@...pe.ca" <jgg@...pe.ca>, "kevin.tian@...el.com" <kevin.tian@...el.com>, "jean-philippe@...aro.org" <jean-philippe@...aro.org>, "eric.auger@...hat.com" <eric.auger@...hat.com>, "Liguozhu (Kenneth)" <liguozhu@...ilicon.com>, "zhangfei.gao@...aro.org" <zhangfei.gao@...aro.org>, "chensihang (A)" <chensihang1@...ilicon.com> Subject: RE: [RFC PATCH v3 1/2] mempinfd: Add new syscall to provide memory pin On Sun, 7 Feb 2021, Song Bao Hua (Barry Song) wrote: > NUMA balancer is just one of many reasons for page migration. Even one > simple alloc_pages() can cause memory migration in just single NUMA > node or UMA system. > > The other reasons for page migration include but are not limited to: > * memory move due to CMA > * memory move due to huge pages creation > > Hardly we can ask users to disable the COMPACTION, CMA and Huge Page > in the whole system. > What about only for mlocked memory, i.e. disable vm.compact_unevictable_allowed? Adding syscalls is a big deal, we can make a reasonable inference that we'll have to support this forever if it's merged. I haven't seen mention of what other unevictable memory *should* be migratable that would be adversely affected if we disable that sysctl. Maybe that gets you part of the way there and there are some other deficiencies, but it seems like a good start would be to describe how CONFIG_NUMA_BALANCING=n + vm.compact_unevcitable_allowed + mlock() doesn't get you mostly there and then look into what's missing. If it's a very compelling case where there simply are no alternatives, it would make sense. Alternative is to find a more generic way, perhaps in combination with vm.compact_unevictable_allowed, to achieve what you're looking to do that can be useful even beyond your originally intended use case.
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