From: Christoph Lameter <cl@linux.com>
To: Andi Kleen <ak@linux.intel.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
linux-mm@kvack.org, Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
x86@kernel.org, Tim Chen <tim.c.chen@linux.intel.com>,
Alex Shi <alex.shu@intel.com>, Jan Beulich <jbeulich@novell.com>,
Robert Richter <robert.richter@amd.com>,
Andy Lutomirski <luto@amacapital.net>,
Andrew Morton <akpm@linux-foundation.org>,
Andrea Arcangeli <aarcange@redhat.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Hugh Dickins <hughd@google.com>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
Mel Gorman <mgorman@suse.de>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH, RFC 0/6] Avoid cache trashing on clearing huge/gigantic page
Date: Wed, 25 Jul 2012 14:38:00 -0500 (CDT) [thread overview]
Message-ID: <alpine.DEB.2.00.1207251434280.4995@router.home> (raw)
In-Reply-To: <20120725192850.GA4952@tassilo.jf.intel.com>
On Wed, 25 Jul 2012, Andi Kleen wrote:
> > why exempt the 4K around the fault address? Is there a regression if that
> > is not exempted?
>
> You would get an immediate cache miss when the faulting instruction
> is reexecuted.
Nope. You would not get cache misses for all cachelines in the 4k range.
Only one.
> > I guess for anonymous huge pages one may assume that there will be at
> > least one write to one cache line in the 4k page. Is it useful to get all
> > the cachelines in the page in the cache.
>
> We did some measurements -- comparing 4K and 2MB with some tracing
> of fault patterns -- and a lot of apps don't use the full 2MB area.
> The apps with THP regressions usually used less than others.
> The patchkit significantly reduced some of the regressions.
Yup they wont use the full 2MB area. But are they using all the cache
lines of the 4k page that we are making hot?
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next prev parent reply other threads:[~2012-07-25 19:38 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-07-20 12:50 Kirill A. Shutemov
2012-07-20 12:50 ` [PATCH, RFC 1/6] THP: Use real address for NUMA policy Kirill A. Shutemov
2012-07-20 12:50 ` [PATCH, RFC 2/6] mm: make clear_huge_page tolerate non aligned address Kirill A. Shutemov
2012-07-20 12:50 ` [PATCH, RFC 3/6] THP: Pass real, not rounded, address to clear_huge_page Kirill A. Shutemov
2012-07-20 12:50 ` [PATCH, RFC 4/6] x86: Add clear_page_nocache Kirill A. Shutemov
2012-07-20 12:50 ` [PATCH, RFC 5/6] mm: make clear_huge_page cache clear only around the fault address Kirill A. Shutemov
2012-07-20 12:50 ` [PATCH, RFC 6/6] x86: switch the 64bit uncached page clear to SSE/AVX v2 Kirill A. Shutemov
2012-07-23 23:30 ` [PATCH, RFC 0/6] Avoid cache trashing on clearing huge/gigantic page Andrew Morton
2012-07-24 14:09 ` Kirill A. Shutemov
2012-07-25 18:51 ` Christoph Lameter
2012-07-25 19:28 ` Andi Kleen
2012-07-25 19:38 ` Christoph Lameter [this message]
2012-08-09 15:18 ` H. Peter Anvin
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