[PATCH 1/12] maps4: add proportional set size accounting in smaps

Matt Mackall
2007-10-26T16:36:47Z

From: Fengguang Wu <wfg@mail.ustc.edu.cn>

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>
Cc: Bernardo Innocenti <bernie@codewiz.org>
Cc: Padraig Brady <P@draigBrady.com>
Cc: Denys Vlasenko <vda.linux@googlemail.com>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Signed-off-by: Matt Mackall <mpm@selenic.com>
Signed-off-by: Fengguang Wu <wfg@mail.ustc.edu.cn>
Cc: Hugh Dickins <hugh@veritas.com>
---

fs/proc/task_mmu.c | 29 ++++++++++++++++++++++++++++-
1 files changed, 28 insertions(+), 1 deletion(-)

Index: l/fs/proc/task_mmu.c
===================================================================
--- l.orig/fs/proc/task_mmu.c 2007-10-16 21:13:47.000000000 -0500
+++ l/fs/proc/task_mmu.c 2007-10-22 15:53:12.000000000 -0500
@@ -114,6 +114,25 @@ static void pad_len_spaces(struct seq_fi
seq_printf(m, "%*c", len, ' ');
}

+/*
+ * 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.
+ *
+ * To keep (accumulated) division errors low, we adopt a 64bit
+ * fixed-point pss counter to minimize division errors. So (pss >>
+ * PSS_SHIFT) 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_SHIFT 12
+
struct mem_size_stats
{
unsigned long resident;
@@ -122,6 +141,7 @@ struct mem_size_stats
unsigned long private_clean;
unsigned long private_dirty;
unsigned long referenced;
+ u64 pss;
};

struct pmd_walker {
@@ -195,6 +215,7 @@ static int show_map_internal(struct seq_
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"
@@ -202,6 +223,7 @@ static int show_map_internal(struct seq_
"Referenced: %8lu kB\n",
(vma->vm_end - vma->vm_start) >> 10,
mss->resident >> 10,
+ (unsigned long)(mss.pss >> (10 + PSS_SHIFT)),
mss->shared_clean >> 10,
mss->shared_dirty >> 10,
mss->private_clean >> 10,
@@ -226,6 +248,7 @@ static void smaps_pte_range(struct vm_ar
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) {
@@ -242,16 +265,19 @@ static void smaps_pte_range(struct vm_ar
/* 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_SHIFT) / mapcount;
} else {
if (pte_dirty(ptent))
mss->private_dirty += PAGE_SIZE;
else
mss->private_clean += PAGE_SIZE;
+ mss->pss += (PAGE_SIZE << PSS_SHIFT);
}
}
pte_unmap_unlock(pte - 1, ptl);