linux-kernel - Re: [PATCH] KVM: replace large kvmalloc allocation with vmalloc

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Message-ID: <163c7948-f41d-986d-871b-9689995ba282@redhat.com>
Date:   Fri, 15 Oct 2021 19:48:05 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        syzbot+e0de2333cbf95ea473e8@...kaller.appspotmail.com
Subject: Re: [PATCH] KVM: replace large kvmalloc allocation with vmalloc

On 15/10/21 19:28, Sean Christopherson wrote:
>>   	for (i = 0; i < KVM_PAGE_TRACK_MAX; i++) {
>>   		slot->arch.gfn_track[i] =
>> -			kvcalloc(npages, sizeof(*slot->arch.gfn_track[i]),
>> -				 GFP_KERNEL_ACCOUNT);
>> +			vcalloc(npages, sizeof(*slot->arch.gfn_track[i]));
> This loses the memcg accounting, which is somewhat important for the theoretical
> 4MiB allocations:-)

True, and in fact 4 MiB is not so theoretical.

> Maybe split out the introduction of vcalloc() to a separate patch (or two) and
> introduce additional helpers to allow passing in gfp_t to e.g. __vzalloc()?

Yes, this is what actually slowed me down this week.This is the bare 
minimum that I can send to Linus right now to avoid the WARN.

I have patches to clean all of this up, but they will have to go throw 
Andrew Morton; he will decide whether to throw them in 5.15 or go 
through stable, but anyway 5.16.1 or .2 should have the accounting back 
at most.

Paolo