Re: [RFC 0/3] mm: process_mrelease: expedited reclaim and auto-kill support

[Suren Baghdasaryan]

On Fri, Apr 24, 2026 at 12:41 AM David Hildenbrand (Arm)
<david@xxxxxxxxxx> wrote:
>
> On 4/24/26 00:36, Suren Baghdasaryan wrote:
> > On Thu, Apr 23, 2026 at 2:50 AM David Hildenbrand (Arm)
> > <david@xxxxxxxxxx> wrote:
> >>
> >> On 4/23/26 09:50, Michal Hocko wrote:
> >>> [...]
> >>>
> >>> This is a very creative/disruptive way to do a memory reclaim. From a
> >>> user POV I would much rather see clean page cache reclaimed before my
> >>> apps start to disappear. But this is obviously your call and your users
> >>> that will care.
> >>>
> >>> Anyway, I still maintain my position. I do not think it is a good
> >>> idea to drop clean page cache as you do not know whether there are other
> >>> users.
> >
> > I'm very much familiar with these issues in Android and really want to
> > find a good solution for them. IIUC, this RFC tries to address 2
> > things at once:
> > 1. handling clean private page cache when reaping memory of a kill victim;
> > 2. addressing a race between kill() and process_release() when
> > process_release() can't happen before the kill() but if it happens too
> > late after the victim passed its exit_mm() then process_release()
> > fails to find the mm to reap. This defeats the purpose of
> > process_release() call because the actual memory (released by
> > exit_mmap()) might not yet be free and a successful process_release()
> > would be very beneficial.
> >
> > I see these two as separate issues and I'm not sure combining them
> > into a single discussion is a good idea.
> >
> >>
> >> IIRC, Johannes raised in the past the we cannot predict the future.
> >>
> >> For example, if an app gets OOM-killed, wouldn't we usually try restarting it,
> >> re-consuming the clean pagecache pages we would be evicting here?
> >
> > Sure, we can't predict which app the user will use next, so when
> > killing we usually kill the least recently used one. That's a
> > reasonable strategy in most cases.
>
> That makes sense. As long as other apps you open next won't need the same
> libraries etc that you just evicted.

True. However shared libraries have a high chance of being used by
more that one process when we kill a background apps. So, while it's
possible that we might evict a page from a library that will be used
shortly after, it's more likely that pages from such libraries would
not be private to the victim. Again, all this is probabilistic and no
ideal strategy exists without knowing the future. All we can do is
optimize for the most likely scenario.

>
> --
> Cheers,
>
> David