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From: Catalin Marinas <catalin.marinas@arm.com>
To: Peter Collingbourne <pcc@google.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>,
	Andrew Morton <akpm@linux-foundation.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Evgenii Stepanov <eugenis@google.com>,
	linux-mm@kvack.org
Subject: Re: [PATCH] mm: introduce reference pages
Date: Tue, 4 Aug 2020 16:27:50 +0100	[thread overview]
Message-ID: <20200804152749.GE31076@gaia> (raw)
In-Reply-To: <CAMn1gO54gTG5f1dVfZHAaXWJRWeOe8BwTAvbk376_pjzcLYRSQ@mail.gmail.com>

On Mon, Aug 03, 2020 at 05:50:32PM -0700, Peter Collingbourne wrote:
> On Mon, Aug 3, 2020 at 5:01 AM Catalin Marinas <catalin.marinas@arm.com> wrote:
> > I think this would work even for the arm64 MTE (though I haven't tried):
> > use memfd_create() to get such file descriptor, mmap() it as MAP_SHARED
> > to populate the initial pattern, mmap() it as MAP_PRIVATE for any
> > subsequent mapping that needs to be copied-on-write.
> 
> That would require a separate mmap() (i.e. separate VMA) for each
> page, no? That sounds like it could be expensive both in terms of VMAs
> and the number of mmap syscalls required (i.e. N/PAGE_SIZE). You could
> decrease these costs by increasing the size of the memfd files to more
> than a page, but that would also increase the amount of memory
> required for the reference pages.

I think I get it now. You'd like a multiple page mmap() to be covered by
a single reference page. The memfd trick wouldn't give you this without
multiple mmap() calls, one for each page.

-- 
Catalin

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linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

WARNING: multiple messages have this Message-ID (diff)
From: Catalin Marinas <catalin.marinas@arm.com>
To: Peter Collingbourne <pcc@google.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>,
	Andrew Morton <akpm@linux-foundation.org>,
	Evgenii Stepanov <eugenis@google.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	linux-mm@kvack.org
Subject: Re: [PATCH] mm: introduce reference pages
Date: Tue, 4 Aug 2020 16:27:50 +0100	[thread overview]
Message-ID: <20200804152749.GE31076@gaia> (raw)
In-Reply-To: <CAMn1gO54gTG5f1dVfZHAaXWJRWeOe8BwTAvbk376_pjzcLYRSQ@mail.gmail.com>

On Mon, Aug 03, 2020 at 05:50:32PM -0700, Peter Collingbourne wrote:
> On Mon, Aug 3, 2020 at 5:01 AM Catalin Marinas <catalin.marinas@arm.com> wrote:
> > I think this would work even for the arm64 MTE (though I haven't tried):
> > use memfd_create() to get such file descriptor, mmap() it as MAP_SHARED
> > to populate the initial pattern, mmap() it as MAP_PRIVATE for any
> > subsequent mapping that needs to be copied-on-write.
> 
> That would require a separate mmap() (i.e. separate VMA) for each
> page, no? That sounds like it could be expensive both in terms of VMAs
> and the number of mmap syscalls required (i.e. N/PAGE_SIZE). You could
> decrease these costs by increasing the size of the memfd files to more
> than a page, but that would also increase the amount of memory
> required for the reference pages.

I think I get it now. You'd like a multiple page mmap() to be covered by
a single reference page. The memfd trick wouldn't give you this without
multiple mmap() calls, one for each page.

-- 
Catalin


  reply	other threads:[~2020-08-04 15:29 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-31 20:32 [PATCH] mm: introduce reference pages Peter Collingbourne
2020-07-31 20:32 ` Peter Collingbourne
2020-08-03  3:28 ` John Hubbard
2020-08-03  3:28   ` John Hubbard
2020-08-03  3:51   ` Matthew Wilcox
2020-08-03  3:51     ` Matthew Wilcox
2020-08-13 22:03     ` Peter Collingbourne
2020-08-13 22:03       ` Peter Collingbourne
2020-08-13 22:03   ` Peter Collingbourne
2020-08-13 22:03     ` Peter Collingbourne
2020-08-03  9:32 ` Kirill A. Shutemov
2020-08-03  9:32   ` Kirill A. Shutemov
2020-08-03 12:01   ` Catalin Marinas
2020-08-03 12:01     ` Catalin Marinas
2020-08-04  0:50     ` Peter Collingbourne
2020-08-04  0:50       ` Peter Collingbourne
2020-08-04 15:27       ` Catalin Marinas [this message]
2020-08-04 15:27         ` Catalin Marinas
2020-08-04 15:48         ` Kirill A. Shutemov
2020-08-04 15:48           ` Kirill A. Shutemov

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