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Date:   Thu, 11 May 2023 20:38:24 -0700
From:   Mike Rapoport <rppt@kernel.org>
To:     Matthew Wilcox <willy@infradead.org>
Cc:     Hugh Dickins <hughd@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        David Hildenbrand <david@redhat.com>,
        Suren Baghdasaryan <surenb@google.com>,
        Qi Zheng <zhengqi.arch@bytedance.com>,
        Russell King <linux@armlinux.org.uk>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Greg Ungerer <gerg@linux-m68k.org>,
        Michal Simek <monstr@monstr.eu>,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        Helge Deller <deller@gmx.de>,
        John David Anglin <dave.anglin@bell.net>,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
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        Michel Lespinasse <michel@lespinasse.org>
Subject: Re: [PATCH 00/23] arch: allow pte_offset_map[_lock]() to fail
Message-ID: <20230512033824.GF4135@kernel.org>
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Hi,

On Thu, May 11, 2023 at 03:02:55PM +0100, Matthew Wilcox wrote:
> On Wed, May 10, 2023 at 09:35:44PM -0700, Hugh Dickins wrote:
> > On Wed, 10 May 2023, Matthew Wilcox wrote:
> > 
> > I don't really understand why you're going down a remove-CONFIG_HIGHPTE
> > route: I thought you were motivated by the awkardness of kmap on large
> > folios; but I don't see how removing HIGHPTE helps with that at all
> > (unless you have a "large page tables" effort in mind, but I doubt it).
> 
> Quite right, my primary concern is filesystem metadata; primarily
> directories as I don't think anybody has ever supported symlinks or
> superblocks larger than 4kB.
> 
> I was thinking that removing CONFIG_HIGHPTE might simplify the page
> fault handling path a little, but now I've looked at it some more, and
> I'm not sure there's any simplification to be had.  It should probably
> use kmap_local instead of kmap_atomic(), though.
 
Removing CONFIG_HIGHPTE will drop several lines and will allow to get rid
of custom __pte_alloc_one on x86.

--
Sincerely yours,
Mike.