linux-kernel - [PATCH v3 00/10] Introduce huge zero page

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Date:	Tue,  2 Oct 2012 18:19:22 +0300
From:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org
Cc:	Andrea Arcangeli <aarcange@...hat.com>,
	Andi Kleen <ak@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	linux-kernel@...r.kernel.org,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: [PATCH v3 00/10] Introduce huge zero page

From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>

During testing I noticed big (up to 2.5 times) memory consumption overhead
on some workloads (e.g. ft.A from NPB) if THP is enabled.

The main reason for that big difference is lacking zero page in THP case.
We have to allocate a real page on read page fault.

A program to demonstrate the issue:
#include <assert.h>
#include <stdlib.h>
#include <unistd.h>

#define MB 1024*1024

int main(int argc, char **argv)
{
        char *p;
        int i;

        posix_memalign((void **)&p, 2 * MB, 200 * MB);
        for (i = 0; i < 200 * MB; i+= 4096)
                assert(p[i] == 0);
        pause();
        return 0;
}

With thp-never RSS is about 400k, but with thp-always it's 200M.
After the patcheset thp-always RSS is 400k too.

v3:
 - fix potential deadlock in refcounting code on preemptive kernel.
 - do not mark huge zero page as movable.
 - fix typo in comment.
 - Reviewed-by tag from Andrea Arcangeli.
v2:
 - Avoid find_vma() if we've already had vma on stack.
   Suggested by Andrea Arcangeli.
 - Implement refcounting for huge zero page.

Kirill A. Shutemov (10):
  thp: huge zero page: basic preparation
  thp: zap_huge_pmd(): zap huge zero pmd
  thp: copy_huge_pmd(): copy huge zero page
  thp: do_huge_pmd_wp_page(): handle huge zero page
  thp: change_huge_pmd(): keep huge zero page write-protected
  thp: change split_huge_page_pmd() interface
  thp: implement splitting pmd for huge zero page
  thp: setup huge zero page on non-write page fault
  thp: lazy huge zero page allocation
  thp: implement refcounting for huge zero page

 Documentation/vm/transhuge.txt |    4 +-
 arch/x86/kernel/vm86_32.c      |    2 +-
 fs/proc/task_mmu.c             |    2 +-
 include/linux/huge_mm.h        |   14 ++-
 include/linux/mm.h             |    8 +
 mm/huge_memory.c               |  307 ++++++++++++++++++++++++++++++++++++----
 mm/memory.c                    |   11 +--
 mm/mempolicy.c                 |    2 +-
 mm/mprotect.c                  |    2 +-
 mm/mremap.c                    |    2 +-
 mm/pagewalk.c                  |    2 +-
 11 files changed, 305 insertions(+), 51 deletions(-)

-- 
1.7.7.6

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