linux-kernel - Re: [PATCH] KVM: x86/mmu: Register MMU shrinker only when necessary

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Message-ID: <ZrzCD-cL4N1DsRaO@google.com>
Date: Wed, 14 Aug 2024 07:41:19 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Liang Chen <liangchen.linux@...il.com>
Cc: pbonzini@...hat.com, kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Vipin Sharma <vipinsh@...gle.com>, David Matlack <dmatlack@...gle.com>
Subject: Re: [PATCH] KVM: x86/mmu: Register MMU shrinker only when necessary

+Vipin and David

On Wed, Aug 14, 2024, Liang Chen wrote:
> The shrinker is allocated with TDP MMU, which is meaningless except for
> nested VMs, and 'count_objects' is also called each time the reclaim
> path tries to shrink slab caches. Let's allocate the shrinker only when
> necessary.

This is definitely not worth the complexity.  In its current form, KVM's shrinker
is quite useless[1], and there were plans to repurpose the shrinker to free pages
from the so called "mmu caches"[2], i.e. free pages that are guaranteed to not be
in use.

Vipin/David, what happened to that series?  Are we still working on it?

[1] https://lore.kernel.org/lkml/Y45dldZnI6OIf+a5@google.com
[2] https://lore.kernel.org/all/20221222023457.1764-2-vipinsh@google.com