[PATCH v2 00/10] Introduce huge zero page

From: Kirill A. Shutemov
Date: Mon Sep 10 2012 - 09:14:35 EST

From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>

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);
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.

- 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 | 303 ++++++++++++++++++++++++++++++++++++----
mm/memory.c | 11 +--
mm/mempolicy.c | 2 +-
mm/mprotect.c | 2 +-
mm/mremap.c | 2 +-
mm/pagewalk.c | 2 +-
11 files changed, 301 insertions(+), 51 deletions(-)


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