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Subject[PATCH] ksm: add vm_stat and meminfo entry to reflect pte mapping to ksm pages
Date
ksm_pages_sharing is updated by ksmd periodically.  In some cases, it cannot 
reflect the actual savings and makes the benchmarks on volatile VMAs very
inaccurate.

This patch add a vm_stat entry and let the /proc/meminfo show information
about how much virutal address pte is being mapped to ksm pages. With default
ksm paramters (pages_to_scan==100 && sleep_millisecs==20), this can result in
50% more accurate averaged savings result for the following test program.
Bigger sleep_millisecs values will increase this deviation.


--- test.c-----
/*
* This test program triggers frequent faults on merged ksm pages but
* still keeps the faulted pages mergeable.
*/
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <unistd.h>
#include <sys/mman.h>

#define MADV_MERGEABLE 12
#define MADV_UNMERGEABLE 13


#define SIZE (1000*1024*1024)
#define SEED 1
#define PAGE_SIZE 4096

int main(int argc, char **argv)
{
char *p;
int j;
long feed = 1, new_feed, tmp;
unsigned int offset;
int status;
int ret;
pid_t child;

child = fork();

p = mmap(NULL, SIZE, PROT_WRITE|PROT_READ,
MAP_PRIVATE|MAP_ANONYMOUS, 0, 0);
if (p == MAP_FAILED) {
printf("mmap error\n");
return 0;
}
ret = madvise(p, SIZE, MADV_MERGEABLE);

if (ret==-1) {
printf("madvise failed \n");
return 0;
}
memset(p, feed, SIZE);

while (1) {
for (j=0; j<SIZE; j+= PAGE_SIZE) {
p[j] *= p[j]*1;
}
}
return 0;
}
----test.c ends-------
Some of the patch lines removes trailing spaces in related files.

Signed-off-by: Nai Xia <nai.xia@gmail.com>
---
diff --git a/fs/proc/meminfo.c b/fs/proc/meminfo.c
index ed257d1..dd0ff82 100644
--- a/fs/proc/meminfo.c
+++ b/fs/proc/meminfo.c
@@ -87,6 +87,9 @@ static int meminfo_proc_show(struct seq_file *m, void *v)
"SUnreclaim: %8lu kB\n"
"KernelStack: %8lu kB\n"
"PageTables: %8lu kB\n"
+#ifdef CONFIG_KSM
+ "KsmSharing: %8lu kB\n"
+#endif
#ifdef CONFIG_QUICKLIST
"Quicklists: %8lu kB\n"
#endif
@@ -145,6 +148,9 @@ static int meminfo_proc_show(struct seq_file *m, void *v)
K(global_page_state(NR_SLAB_UNRECLAIMABLE)),
global_page_state(NR_KERNEL_STACK) * THREAD_SIZE / 1024,
K(global_page_state(NR_PAGETABLE)),
+#ifdef CONFIG_KSM
+ K(global_page_state(NR_KSM_PAGES_SHARING)),
+#endif
#ifdef CONFIG_QUICKLIST
K(quicklist_total_size()),
#endif
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 02ecb01..01450e3 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -115,6 +115,9 @@ enum zone_stat_item {
NUMA_OTHER, /* allocation from other node */
#endif
NR_ANON_TRANSPARENT_HUGEPAGES,
+#ifdef CONFIG_KSM
+ NR_KSM_PAGES_SHARING,
+#endif
NR_VM_ZONE_STAT_ITEMS };

/*
@@ -344,7 +347,7 @@ struct zone {
ZONE_PADDING(_pad1_)

/* Fields commonly accessed by the page reclaim scanner */
- spinlock_t lru_lock;
+ spinlock_t lru_lock;
struct zone_lru {
struct list_head list;
} lru[NR_LRU_LISTS];
@@ -722,7 +725,7 @@ static inline int is_normal_idx(enum zone_type idx)
}

/**
- * is_highmem - helper function to quickly check if a struct zone is a
+ * is_highmem - helper function to quickly check if a struct zone is a
* highmem zone or not. This is an attempt to keep references
* to ZONE_{DMA/NORMAL/HIGHMEM/etc} in general code to a
minimum.
* @zone - pointer to struct zone variable
diff --git a/mm/ksm.c b/mm/ksm.c
index c2b2a94..3c22d30 100644
--- a/mm/ksm.c
+++ b/mm/ksm.c
@@ -897,6 +897,7 @@ static int try_to_merge_one_page(struct vm_area_struct
*vma,
*/
if (write_protect_page(vma, page, &orig_pte) == 0) {
if (!kpage) {
+ long mapcount = page_mapcount(page);
/*
* While we hold page lock, upgrade page from
* PageAnon+anon_vma to PageKsm+NULL stable_node:
@@ -904,6 +905,10 @@ static int try_to_merge_one_page(struct vm_area_struct
*vma,
*/
set_page_stable_node(page, NULL);
mark_page_accessed(page);
+ if (mapcount)
+ add_zone_page_state(page_zone(page),
+ NR_KSM_PAGES_SHARING,
+ mapcount);
err = 0;
} else if (pages_identical(page, kpage))
err = replace_page(vma, page, kpage, orig_pte);
diff --git a/mm/memory.c b/mm/memory.c
index 8e8c183..d86abe9 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -719,6 +719,8 @@ copy_one_pte(struct mm_struct *dst_mm, struct mm_struct
*src_mm,
rss[MM_ANONPAGES]++;
else
rss[MM_FILEPAGES]++;
+ if (PageKsm(page)) /* follows page_dup_rmap() */
+ inc_zone_page_state(page, NR_KSM_PAGES_SHARING);
}

out_set_pte:
@@ -1423,7 +1425,7 @@ int __get_user_pages(struct task_struct *tsk, struct
mm_struct *mm,

VM_BUG_ON(!!pages != !!(gup_flags & FOLL_GET));

- /*
+ /*
* Require read or write permissions.
* If FOLL_FORCE is set, we only require the "MAY" flags.
*/
diff --git a/mm/rmap.c b/mm/rmap.c
index f21f4a1..0d7ab31 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -801,9 +801,9 @@ void page_move_anon_rmap(struct page *page,

/**
* __page_set_anon_rmap - set up new anonymous rmap
- * @page: Page to add to rmap
+ * @page: Page to add to rmap
* @vma: VM area to add page to.
- * @address: User virtual address of the mapping
+ * @address: User virtual address of the mapping
* @exclusive: the page is exclusively owned by the current process
*/
static void __page_set_anon_rmap(struct page *page,
@@ -889,8 +889,10 @@ void do_page_add_anon_rmap(struct page *page,
__inc_zone_page_state(page,
NR_ANON_TRANSPARENT_HUGEPAGES);
}
- if (unlikely(PageKsm(page)))
+ if (unlikely(PageKsm(page))) {
+ __inc_zone_page_state(page, NR_KSM_PAGES_SHARING);
return;
+ }

VM_BUG_ON(!PageLocked(page));
VM_BUG_ON(address < vma->vm_start || address >= vma->vm_end);
@@ -949,6 +951,9 @@ void page_add_file_rmap(struct page *page)
*/
void page_remove_rmap(struct page *page)
{
+ if (PageKsm(page))
+ __dec_zone_page_state(page, NR_KSM_PAGES_SHARING);
+
/* page still mapped by someone else? */
if (!atomic_add_negative(-1, &page->_mapcount))
return;
---



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