From: "H. Peter Anvin" <hpa@linux.intel.com>
To: Andrea Arcangeli <aarcange@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
linux-mm@kvack.org, Andi Kleen <ak@linux.intel.com>,
linux-kernel@vger.kernel.org,
"Kirill A. Shutemov" <kirill@shutemov.name>
Subject: Re: [PATCH, RFC 0/9] Introduce huge zero page
Date: Thu, 16 Aug 2012 16:08:30 -0700 [thread overview]
Message-ID: <502D7D6E.8090303@linux.intel.com> (raw)
In-Reply-To: <20120816194024.GP11188@redhat.com>
On 08/16/2012 12:40 PM, Andrea Arcangeli wrote:
> Hi Andrew,
>
> On Thu, Aug 16, 2012 at 12:20:23PM -0700, Andrew Morton wrote:
>> That's a pretty big improvement for a rather fake test case. I wonder
>> how much benefit we'd see with real workloads?
>
> The same discussion happened about the zero page in general and
> there's no easy answer. I seem to recall that it was dropped at some
> point and then we reintroduced the zero page later.
>
> Most of the time it won't be worth it, it's just a few pathological
> compute loads that benefits IIRC. So I'm overall positive about it
> (after it's stable).
>
> Because this is done the right way (i.e. to allocate an hugepage at
> the first wp fault, and to fallback exclusively if compaction fails)
> it will help much less than the 4k zero pages if the zero pages are
> scattered over the address space and not contiguous (it only helps if
> there are 512 of them in a row). OTOH if they're contiguous, the huge
> zero pages will perform better than the 4k zero pages.
>
One thing that I asked for testing a "virtual zero page" where the same
page (or N pages for N-way page coloring) is reused across a page table.
It would have worse TLB performance but likely *much* better cache
behavior.
-hpa
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next prev parent reply other threads:[~2012-08-16 23:08 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-09 9:08 [PATCH, RFC 0/9] Introduce huge zero page Kirill A. Shutemov
2012-08-09 9:08 ` [PATCH, RFC 1/9] thp: huge zero page: basic preparation Kirill A. Shutemov
2012-08-09 9:08 ` [PATCH, RFC 2/9] thp: zap_huge_pmd(): zap huge zero pmd Kirill A. Shutemov
2012-08-09 9:08 ` [PATCH, RFC 3/9] thp: copy_huge_pmd(): copy huge zero page Kirill A. Shutemov
2012-08-09 9:08 ` [PATCH, RFC 4/9] thp: do_huge_pmd_wp_page(): handle " Kirill A. Shutemov
2012-08-09 9:08 ` [PATCH, RFC 5/9] thp: change_huge_pmd(): keep huge zero page write-protected Kirill A. Shutemov
2012-08-09 9:08 ` [PATCH, RFC 6/9] thp: add address parameter to split_huge_page_pmd() Kirill A. Shutemov
2012-08-16 19:42 ` Andrea Arcangeli
2012-08-17 7:49 ` Kirill A. Shutemov
2012-08-09 9:08 ` [PATCH, RFC 7/9] thp: implement splitting pmd for huge zero page Kirill A. Shutemov
2012-08-16 19:27 ` Andrea Arcangeli
2012-08-17 8:12 ` Kirill A. Shutemov
2012-08-17 16:33 ` Andrea Arcangeli
2012-08-31 14:06 ` Kirill A. Shutemov
2012-08-09 9:08 ` [PATCH, RFC 8/9] thp: setup huge zero page on non-write page fault Kirill A. Shutemov
2012-08-09 9:08 ` [PATCH, RFC 9/9] thp: lazy huge zero page allocation Kirill A. Shutemov
2012-08-10 3:49 ` [PATCH, RFC 0/9] Introduce huge zero page Wanpeng Li
2012-08-10 3:49 ` Wanpeng Li
2012-08-10 10:33 ` Kirill A. Shutemov
2012-08-11 1:10 ` Wanpeng Li
2012-08-11 1:10 ` Wanpeng Li
2012-08-16 19:20 ` Andrew Morton
2012-08-16 19:40 ` Andrea Arcangeli
2012-08-16 23:08 ` H. Peter Anvin [this message]
2012-08-16 23:12 ` Andi Kleen
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