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Subject[PATCH 1/4] maps: PSS(proportional set size) accounting in smaps
The "proportional set size" (PSS) of a process is the count of pages it has in
memory, where each page is divided by the number of processes sharing it. So if
a process has 1000 pages all to itself, and 1000 shared with one other process,
its PSS will be 1500.
- lwn.net: "ELC: How much memory are applications really using?"

The PSS proposed by Matt Mackall is a very nice metic for measuring an process's
memory footprint. So collect and export it via /proc/<pid>/smaps.

Matt Mackall's pagemap/kpagemap and John Berthels's exmap can also do the job.
They are comprehensive tools. But for PSS, let's do it in the simple way.


Cc: John Berthels <jjberthels@gmail.com>
Acked-by: Matt Mackall <mpm@selenic.com>
Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
---
fs/proc/task_mmu.c | 29 ++++++++++++++++++++++++++++-
1 file changed, 28 insertions(+), 1 deletion(-)
--- linux-2.6.23-rc2-mm2.orig/fs/proc/task_mmu.c
+++ linux-2.6.23-rc2-mm2/fs/proc/task_mmu.c
@@ -324,6 +324,27 @@ struct mem_size_stats
unsigned long private_clean;
unsigned long private_dirty;
unsigned long referenced;
+
+ /*
+ * Proportional Set Size(PSS): my share of RSS.
+ *
+ * PSS of a process is the count of pages it has in memory, where each
+ * page is divided by the number of processes sharing it. So if a
+ * process has 1000 pages all to itself, and 1000 shared with one other
+ * process, its PSS will be 1500. - Matt Mackall, lwn.net
+ */
+ u64 pss;
+ /*
+ * To keep (accumulated) division errors low, we adopt 64bit pss and
+ * use some low bits for division errors. So (pss >> PSS_ERROR_BITS)
+ * would be the real byte count.
+ *
+ * A shift of 12 before division means(assuming 4K page size):
+ * - 1M 3-user-pages add up to 8KB errors;
+ * - supports mapcount up to 2^24, or 16M;
+ * - supports PSS up to 2^52 bytes, or 4PB.
+ */
+#define PSS_ERROR_BITS 12
};

struct smaps_arg
@@ -341,6 +362,7 @@ static int smaps_pte_range(pmd_t *pmd, u
pte_t *pte, ptent;
spinlock_t *ptl;
struct page *page;
+ int mapcount;

pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
for (; addr != end; pte++, addr += PAGE_SIZE) {
@@ -357,16 +379,19 @@ static int smaps_pte_range(pmd_t *pmd, u
/* Accumulate the size in pages that have been accessed. */
if (pte_young(ptent) || PageReferenced(page))
mss->referenced += PAGE_SIZE;
- if (page_mapcount(page) >= 2) {
+ mapcount = page_mapcount(page);
+ if (mapcount >= 2) {
if (pte_dirty(ptent))
mss->shared_dirty += PAGE_SIZE;
else
mss->shared_clean += PAGE_SIZE;
+ mss->pss += (PAGE_SIZE << PSS_ERROR_BITS) / mapcount;
} else {
if (pte_dirty(ptent))
mss->private_dirty += PAGE_SIZE;
else
mss->private_clean += PAGE_SIZE;
+ mss->pss += (PAGE_SIZE << PSS_ERROR_BITS);
}
}
pte_unmap_unlock(pte - 1, ptl);
@@ -395,6 +420,7 @@ static int show_smap(struct seq_file *m,
seq_printf(m,
"Size: %8lu kB\n"
"Rss: %8lu kB\n"
+ "Pss: %8lu kB\n"
"Shared_Clean: %8lu kB\n"
"Shared_Dirty: %8lu kB\n"
"Private_Clean: %8lu kB\n"
@@ -402,6 +428,7 @@ static int show_smap(struct seq_file *m,
"Referenced: %8lu kB\n",
(vma->vm_end - vma->vm_start) >> 10,
sarg.mss.resident >> 10,
+ (unsigned long)(sarg.mss.pss >> (10 + PSS_ERROR_BITS)),
sarg.mss.shared_clean >> 10,
sarg.mss.shared_dirty >> 10,
sarg.mss.private_clean >> 10,
--
-
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