From: Paolo Bonzini <pbonzini@redhat.com>
To: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Dave Hansen <dave.hansen@intel.com>,
Dominik Dingel <dingel@linux.vnet.ibm.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, Mel Gorman <mgorman@suse.de>,
Michal Hocko <mhocko@suse.cz>, Rik van Riel <riel@redhat.com>,
Andrea Arcangeli <aarcange@redhat.com>,
Andy Lutomirski <luto@amacapital.net>,
"Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
Bob Liu <lliubbo@gmail.com>,
Christian Borntraeger <borntraeger@de.ibm.com>,
Cornelia Huck <cornelia.huck@de.ibm.com>,
Gleb Natapov <gleb@kernel.org>,
Heiko Carstens <heiko.carstens@de.ibm.com>,
"H. Peter Anvin" <hpa@linux.intel.com>,
Hugh Dickins <hughd@google.com>, Ingo Molnar <mingo@kernel.org>,
Jianyu Zhan <nasa4836@gmail.com>,
Johannes Weiner <hannes@cmpxchg.org>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Konstantin Weitz <konstantin.weitz@gmail.com>,
kvm@vger.kernel.org, linux390@de.ibm.com,
linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
Sasha Levin <sasha.levin@oracle.com>
Subject: Re: [PATCH 2/4] mm: introduce new VM_NOZEROPAGE flag
Date: Tue, 21 Oct 2014 10:11:43 +0200 [thread overview]
Message-ID: <5446153F.6030407@redhat.com> (raw)
In-Reply-To: <20141021081131.641c6104@mschwide>
On 10/21/2014 08:11 AM, Martin Schwidefsky wrote:
>> I agree with Dave (I thought I disagreed, but I changed my mind while
>> writing down my thoughts). Just define mm_forbids_zeropage in
>> arch/s390/include/asm, and make it return mm->context.use_skey---with a
>> comment explaining how this is only for processes that use KVM, and then
>> only for guests that use storage keys.
>
> The mm_forbids_zeropage() sure will work for now, but I think a vma flag
> is the better solution. This is analog to VM_MERGEABLE or VM_NOHUGEPAGE,
> the best solution would be to only mark those vmas that are mapped to
> the guest. That we have not found a way to do that yet in a sensible way
> does not change the fact that "no-zero-page" is a per-vma property, no?
I agree it should be per-VMA. However, right now the code is
complicated unnecessarily by making it a per-VMA flag. Also, setting
the flag per VMA should probably be done in
kvm_arch_prepare_memory_region together with some kind of storage key
notifier. This is not very much like Dominik's patch. All in all,
mm_forbids_zeropage() provides a non-intrusive and non-controversial way
to fix the bug. Later on, switching to vma_forbids_zeropage() will be
trivial as far as mm/ code is concerned.
> But if you insist we go with the mm_forbids_zeropage() until we find a
> clever way to distinguish the guest vmas from the qemu ones.
Yeah, I think it is simpler for now.
Paolo
next prev parent reply other threads:[~2014-10-21 8:12 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-17 14:09 [PATCH 0/4] mm: new flag to forbid zero page mappings for a vma Dominik Dingel
2014-10-17 14:09 ` [PATCH 1/4] s390/mm: recfactor global pgste updates Dominik Dingel
2014-10-17 14:09 ` [PATCH 2/4] mm: introduce new VM_NOZEROPAGE flag Dominik Dingel
2014-10-17 22:04 ` Dave Hansen
2014-10-18 14:49 ` Dominik Dingel
2014-10-18 16:28 ` Dave Hansen
2014-10-20 18:14 ` Paolo Bonzini
2014-10-21 6:11 ` Martin Schwidefsky
2014-10-21 8:11 ` Paolo Bonzini [this message]
2014-10-21 11:20 ` Dominik Dingel
2014-10-17 14:09 ` [PATCH 3/4] s390/mm: prevent and break zero page mappings in case of storage keys Dominik Dingel
2014-10-17 14:09 ` [PATCH 4/4] s390/mm: disable KSM for storage key enabled pages Dominik Dingel
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