maps4: add 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>
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>
Cc: Dave Hansen <haveblue@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 27 insertions, 1 deletions

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 8043a3eab52c..8952ce70315e 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -114,6 +114,25 @@ static void pad_len_spaces(struct seq_file *m, int len)
         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_file *m, void *v, struct mem_size_stats
                 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_file *m, void *v, struct mem_size_stats
                            "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_area_struct *vma, pmd_t *pmd,
         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_area_struct *vma, pmd_t *pmd,
                 /* 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);