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

David Hildenbrand (Arm)
2026-04-23T09:50:04Z

On 4/23/26 09:50, Michal Hocko wrote:
> 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.

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?

Just a thought.

--
Cheers,

David