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Date: Wed, 5 Jul 2017 13:18:18 +1000 From: Balbir Singh <bsingharora@...il.com> To: Michal Hocko <mhocko@...nel.org> Cc: Jérôme Glisse <jglisse@...hat.com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>, John Hubbard <jhubbard@...dia.com>, David Nellans <dnellans@...dia.com>, Dan Williams <dan.j.williams@...el.com>, Johannes Weiner <hannes@...xchg.org>, Vladimir Davydov <vdavydov.dev@...il.com>, "cgroups@...r.kernel.org" <cgroups@...r.kernel.org> Subject: Re: [PATCH 4/5] mm/memcontrol: allow to uncharge page without using page->lru field On Tue, Jul 4, 2017 at 10:51 PM, Michal Hocko <mhocko@...nel.org> wrote: > On Mon 03-07-17 17:14:14, Jérôme Glisse wrote: >> HMM pages (private or public device pages) are ZONE_DEVICE page and >> thus you can not use page->lru fields of those pages. This patch >> re-arrange the uncharge to allow single page to be uncharge without >> modifying the lru field of the struct page. >> >> There is no change to memcontrol logic, it is the same as it was >> before this patch. > > What is the memcg semantic of the memory? Why is it even charged? AFAIR > this is not a reclaimable memory. If yes how are we going to deal with > memory limits? What should happen if go OOM? Does killing an process > actually help to release that memory? Isn't it pinned by a device? > > For the patch itself. It is quite ugly but I haven't spotted anything > obviously wrong with it. It is the memcg semantic with this class of > memory which makes me worried. > This is the HMM CDM case. Memory is normally malloc'd and then migrated to ZONE_DEVICE or vice-versa. One of the things we did discuss was seeing ZONE_DEVICE memory in user page tables. Balbir Singh.
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