linux-kernel - Re: [PATCH] mm: allow huge kvmalloc() calls if they're accounted to memcg

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Date:   Sat, 16 Oct 2021 08:39:49 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     KVM list <kvm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Sean Christopherson <seanjc@...gle.com>,
        Willy Tarreau <w@....eu>, Kees Cook <keescook@...omium.org>,
        syzbot+e0de2333cbf95ea473e8@...kaller.appspotmail.com
Subject: Re: [PATCH] mm: allow huge kvmalloc() calls if they're accounted to memcg

On Fri, Oct 15, 2021 at 11:43 PM Paolo Bonzini <pbonzini@...hat.com> wrote:
>
> Use memcg accounting as evidence that the crazy large allocations are
> expected---in which case, it is indeed a good idea to have them
> properly accounted---and exempt them from the warning.

This is not sensible.

The big allocation warnings are not about whether we have the memory
or not, or about whether it's accounted or not.

It's about bugs and overflows. Which we've had.

At least GFP_NOWARN would be somewhat sensible - although still wrong.
It should really be about "I've been careful with growing my
allocations", not about whether accounting or similar should be
disabled.

If the allocations really are expected to be that big, and it's
actually valid, just do vmalloc(), which doesn't warn.

                      Linus