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Commit 9a840895 authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
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ksm: identify PageKsm pages 



KSM will need to identify its kernel merged pages unambiguously, and
/proc/kpageflags will probably like to do so too.

Since KSM will only be substituting anonymous pages, statistics are best
preserved by making a PageKsm page a special PageAnon page: one with no
anon_vma.

But KSM then needs its own page_add_ksm_rmap() - keep it in ksm.h near
PageKsm; and do_wp_page() must COW them, unlike singly mapped PageAnons.

Signed-off-by: default avatarHugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: default avatarChris Wright <chrisw@redhat.com>
Signed-off-by: default avatarIzik Eidus <ieidus@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 21333b2b

fs/proc/page.c

+5 −0
Original line number Diff line number Diff line
@@ -2,6 +2,7 @@ 
#include <linux/compiler.h>

#include <linux/fs.h>

#include <linux/init.h>

#include <linux/ksm.h>

#include <linux/mm.h>

#include <linux/mmzone.h>

#include <linux/proc_fs.h>
@@ -95,6 +96,8 @@ static const struct file_operations proc_kpagecount_operations = { 
#define KPF_UNEVICTABLE		18

#define KPF_NOPAGE		20



#define KPF_KSM			21



/* kernel hacking assistances

 * WARNING: subject to change, never rely on them!

 */
@@ -137,6 +140,8 @@ static u64 get_uflags(struct page *page) 
		u |= 1 << KPF_MMAP;

	if (PageAnon(page))

		u |= 1 << KPF_ANON;

	if (PageKsm(page))

		u |= 1 << KPF_KSM;



	/*

	 * compound pages: export both head/tail info

include/linux/ksm.h

+29 −0
Original line number Diff line number Diff line
@@ -10,6 +10,7 @@ 
#include <linux/bitops.h>

#include <linux/mm.h>

#include <linux/sched.h>

#include <linux/vmstat.h>



#ifdef CONFIG_KSM

int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
@@ -29,6 +30,27 @@ static inline void ksm_exit(struct mm_struct *mm) 
	if (test_bit(MMF_VM_MERGEABLE, &mm->flags))

		__ksm_exit(mm);

}



/*

 * A KSM page is one of those write-protected "shared pages" or "merged pages"

 * which KSM maps into multiple mms, wherever identical anonymous page content

 * is found in VM_MERGEABLE vmas.  It's a PageAnon page, with NULL anon_vma.

 */

static inline int PageKsm(struct page *page)

{

	return ((unsigned long)page->mapping == PAGE_MAPPING_ANON);

}



/*

 * But we have to avoid the checking which page_add_anon_rmap() performs.

 */

static inline void page_add_ksm_rmap(struct page *page)

{

	if (atomic_inc_and_test(&page->_mapcount)) {

		page->mapping = (void *) PAGE_MAPPING_ANON;

		__inc_zone_page_state(page, NR_ANON_PAGES);

	}

}

#else  /* !CONFIG_KSM */



static inline int ksm_madvise(struct vm_area_struct *vma, unsigned long start,
@@ -45,6 +67,13 @@ static inline int ksm_fork(struct mm_struct *mm, struct mm_struct *oldmm) 
static inline void ksm_exit(struct mm_struct *mm)

{

}



static inline int PageKsm(struct page *page)

{

	return 0;

}



/* No stub required for page_add_ksm_rmap(page) */

#endif /* !CONFIG_KSM */



#endif

mm/memory.c

+2 −1
Original line number Diff line number Diff line
@@ -45,6 +45,7 @@ 
#include <linux/swap.h>

#include <linux/highmem.h>

#include <linux/pagemap.h>

#include <linux/ksm.h>

#include <linux/rmap.h>

#include <linux/module.h>

#include <linux/delayacct.h>
@@ -1974,7 +1975,7 @@ static int do_wp_page(struct mm_struct *mm, struct vm_area_struct *vma, 
	 * Take out anonymous pages first, anonymous shared vmas are

	 * not dirty accountable.

	 */

	if (PageAnon(old_page)) {

	if (PageAnon(old_page) && !PageKsm(old_page)) {

		if (!trylock_page(old_page)) {

			page_cache_get(old_page);

			pte_unmap_unlock(page_table, ptl);