linux-kernel - Re: [PATCH v1 4/7] arm64/pgtable: support __HAVE_ARCH_PTE_SWP

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Message-ID: <10851f31-632c-5fb4-a941-3dccc46e5156@redhat.com>
Date:   Tue, 22 Mar 2022 10:46:38 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Hugh Dickins <hughd@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        David Rientjes <rientjes@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        John Hubbard <jhubbard@...dia.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Yang Shi <shy828301@...il.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Matthew Wilcox <willy@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>,
        Michal Hocko <mhocko@...nel.org>,
        Nadav Amit <namit@...are.com>, Rik van Riel <riel@...riel.com>,
        Roman Gushchin <guro@...com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Peter Xu <peterx@...hat.com>,
        Donald Dutile <ddutile@...hat.com>,
        Christoph Hellwig <hch@....de>,
        Oleg Nesterov <oleg@...hat.com>, Jan Kara <jack@...e.cz>,
        Liang Zhang <zhangliang5@...wei.com>,
        Pedro Gomes <pedrodemargomes@...il.com>,
        Oded Gabbay <oded.gabbay@...il.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, linux-mm@...ck.org,
        x86@...nel.org, linux-arm-kernel@...ts.infradead.org,
        linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org
Subject: Re: [PATCH v1 4/7] arm64/pgtable: support
 __HAVE_ARCH_PTE_SWP_EXCLUSIVE

On 21.03.22 19:27, Catalin Marinas wrote:
> On Mon, Mar 21, 2022 at 05:44:05PM +0000, Will Deacon wrote:
>> On Mon, Mar 21, 2022 at 04:07:48PM +0100, David Hildenbrand wrote:
>>> So the example you gave cannot possibly have that bit set. From what I
>>> understand, it should be fine. But I have no real preference: I can also
>>> just stick to the original patch, whatever you prefer.
>>
>> I think I'd prefer to stay on the safe side and stick with bit 2 as you
>> originally proposed. If we need to support crazy numbers of swapfiles
>> in future then we can revisit the idea of allocating bit 1.
> 
> Sounds fine to me. David, feel free to keep my reviewed-by on the
> original patch.
> 

Thanks both, I'll add the following comment to the patch:

"Note that we might be able to reuse bit 1, but reusing bit 1 turned out
 problematic in the past for PROT_NONE handling; so let's play safe and
 use another bit."


-- 
Thanks,

David / dhildenb