linux-kernel - Re: [PATCH 4/5] mm/memcontrol: allow to uncharge page without using page->lru field

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Date:   Mon, 10 Jul 2017 14:10:53 -0400
From:   Jerome Glisse <jglisse@...hat.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        John Hubbard <jhubbard@...dia.com>,
        David Nellans <dnellans@...dia.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Balbir Singh <bsingharora@...il.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        cgroups@...r.kernel.org
Subject: Re: [PATCH 4/5] mm/memcontrol: allow to uncharge page without using
 page->lru field

On Mon, Jul 10, 2017 at 07:48:58PM +0200, Michal Hocko wrote:
> On Mon 10-07-17 12:54:21, Jerome Glisse wrote:
> > On Mon, Jul 10, 2017 at 06:36:52PM +0200, Michal Hocko wrote:
> > > On Mon 10-07-17 12:25:42, Jerome Glisse wrote:
> > > [...]
> > > > Bottom line is that we can always free and uncharge device memory
> > > > page just like any regular page.
> > > 
> > > OK, this answers my earlier question. Then it should be feasible to
> > > charge this memory. There are still some things to handle. E.g. how do
> > > we consider this memory during oom victim selection (this is not
> > > accounted as an anonymous memory in get_mm_counter, right?), maybe others.
> > > But the primary point is that nobody pins the memory outside of the
> > > mapping.
> > 
> > At this point it is accounted as a regular page would be (anonymous, file
> > or share memory). I wanted mm_counters to reflect memcg but i can untie
> > that.
> 
> I am not sure I understand. If the device memory is accounted to the
> same mm counter as the original page then it is correct. I will try to
> double check the implementation (hopefully soon).

It is accounted like the original page. By same as memcg i mean i made
the same kind of choice for mm counter than i made for memcg. It is
all in the migrate code (migrate.c) ie i don't touch any of the mm
counter when migrating page.

Jérôme