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

[Michal Hocko <mhocko@suse.com>]

On Mon 20-04-26 14:53:23, Minchan Kim wrote:
> On Fri, Apr 17, 2026 at 09:11:21AM +0200, Michal Hocko wrote:
[...]
> > Yes. All which make sense, really. I am still not convinced about the
> > clean page cache because that just seems like a hack to workaround wrong
> > userspace oom heuristics.
> 
> I see it a bit differently. When paltform decides to kill a process
> to free up memory, they want that memory back right away.
> 
> So it doesn't make much sense for the kernel to ignore that and leave the clean
> file pages to be picked up slowly by kswapd later.
> 
> In some aspects, you can think of LMKD as a more specialized, userspace version
> of kswapd. It has high-level knowledge of process priorities and knows exactly
> which process is safe to kill to get memory instantly. The kernel's kswapd,
> however, operates globally without this specific process-level awareness, which
> makes it less suited for this kind of targeted reclamation.
> 
> If we force LMKD to rely on the slower global kswapd to actually free the clean
> pages, it defeats the whole purpose of targeting a specific process.
> 
> So letting process_mrelease speed this up isn't a hack at all. It's just helping
> the kernel do what the admin wanted in the first place: fast, targeted memory.

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 am NOT NAKing this patch though but please make sure you have a
wider support for this idea before this gets merged. Also make sure that
all the above reasoning is part of the changelog if you want to get this
merged.

-- 
Michal Hocko
SUSE Labs