From: "H. Peter Anvin" <hpa@linux.intel.com>
To: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, Andi Kleen <ak@linux.intel.com>,
linux-kernel@vger.kernel.org,
"Kirill A. Shutemov" <kirill@shutemov.name>,
Arnd Bergmann <arnd@arndb.de>, Ingo Molnar <mingo@kernel.org>,
linux-arch@vger.kernel.org
Subject: Re: [PATCH 0/3] Virtual huge zero page
Date: Mon, 01 Oct 2012 08:34:28 -0700 [thread overview]
Message-ID: <5069B804.6040902@linux.intel.com> (raw)
In-Reply-To: <20120929134811.GC26989@redhat.com>
On 09/29/2012 06:48 AM, Andrea Arcangeli wrote:
>
> There would be a small cache benefit here... but even then some first
> level caches are virtually indexed IIRC (always physically tagged to
> avoid the software to notice) and virtually indexed ones won't get any
> benefit.
>
Not quite. The virtual indexing is limited to a few bits (e.g. three
bits on K8); the right way to deal with that is to color the zeropage,
both the regular one and the virtual one (the virtual one would circle
through all the colors repeatedly.)
The cache difference, therefore, is *huge*.
> I guess it won't make a whole lot of difference but my preference is
> for the previous implementation that always guaranteed huge TLB
> entries whenever possible. Said that I'm fine either ways so if
> somebody has strong reasons for wanting this one, I'd like to hear
> about it.
It's a performance tradeoff, and it can, and should, be measured.
-hpa
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next prev parent reply other threads:[~2012-10-01 15:34 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-28 23:37 [PATCH 0/3] Virtual huge zero page Kirill A. Shutemov
2012-09-28 23:37 ` [PATCH 1/3] asm-generic: introduce pmd_special() and pmd_mkspecial() Kirill A. Shutemov
2012-09-28 23:37 ` [PATCH 2/3] mm, thp: implement virtual huge zero page Kirill A. Shutemov
2012-09-28 23:37 ` [PATCH 3/3] x86: implement HAVE_PMD_SPECAIL Kirill A. Shutemov
2012-09-29 13:48 ` [PATCH 0/3] Virtual huge zero page Andrea Arcangeli
2012-09-29 14:30 ` Andi Kleen
2012-09-29 14:37 ` Andrea Arcangeli
2012-10-01 13:49 ` Kirill A. Shutemov
2012-10-01 16:14 ` Andrea Arcangeli
2012-10-01 17:18 ` Kirill A. Shutemov
2012-10-01 15:34 ` H. Peter Anvin [this message]
2012-10-01 16:31 ` Andrea Arcangeli
2012-10-01 17:03 ` H. Peter Anvin
2012-10-01 17:15 ` Kirill A. Shutemov
2012-10-01 18:03 ` Andrea Arcangeli
2012-10-01 17:26 ` Andrea Arcangeli
2012-10-01 17:33 ` H. Peter Anvin
2012-10-01 17:36 ` Kirill A. Shutemov
2012-10-01 17:37 ` H. Peter Anvin
2012-10-01 17:44 ` Kirill A. Shutemov
2012-10-01 17:52 ` H. Peter Anvin
2012-10-01 18:56 ` Kirill A. Shutemov
2012-10-01 18:05 ` Andrea Arcangeli
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