Linux-mm Archive on
 help / color / Atom feed
	Luigi Semenzato <>
Subject: [PATCH 1/1 v5] mm: smaps: split PSS into components
Date: Wed, 26 Jun 2019 16:43:33 -0700
Message-ID: <> (raw)

From: Luigi Semenzato <>

Report separate components (anon, file, and shmem)
for PSS in smaps_rollup.

This helps understand and tune the memory manager behavior
in consumer devices, particularly mobile devices.  Many of
them (e.g. chromebooks and Android-based devices) use zram
for anon memory, and perform disk reads for discarded file
pages.  The difference in latency is large (e.g. reading
a single page from SSD is 30 times slower than decompressing
a zram page on one popular device), thus it is useful to know
how much of the PSS is anon vs. file.

All the information is already present in /proc/pid/smaps,
but much more expensive to obtain because of the large size
of that procfs entry.

This patch also removes a small code duplication in smaps_account,
which would have gotten worse otherwise.

Also updated Documentation/filesystems/proc.txt (the smaps
section was a bit stale, and I added a smaps_rollup section)
and Documentation/ABI/testing/procfs-smaps_rollup.

Acked-by: Yu Zhao <>
Signed-off-by: Luigi Semenzato <>
 Documentation/ABI/testing/procfs-smaps_rollup | 14 ++-
 Documentation/filesystems/proc.txt            | 41 +++++++--
 fs/proc/task_mmu.c                            | 92 +++++++++++++------
 3 files changed, 105 insertions(+), 42 deletions(-)

diff --git a/Documentation/ABI/testing/procfs-smaps_rollup b/Documentation/ABI/testing/procfs-smaps_rollup
index 0a54ed0d63c9..274df44d8b1b 100644
--- a/Documentation/ABI/testing/procfs-smaps_rollup
+++ b/Documentation/ABI/testing/procfs-smaps_rollup
@@ -3,18 +3,28 @@ Date:		August 2017
 Contact:	Daniel Colascione <>
 		This file provides pre-summed memory information for a
-		process.  The format is identical to /proc/pid/smaps,
+		process.  The format is almost identical to /proc/pid/smaps,
 		except instead of an entry for each VMA in a process,
 		smaps_rollup has a single entry (tagged "[rollup]")
 		for which each field is the sum of the corresponding
 		fields from all the maps in /proc/pid/smaps.
-		For more details, see the procfs man page.
+		Additionally, the fields Pss_Anon, Pss_File and Pss_Shmem
+		are not present in /proc/pid/smaps.  These fields represent
+		the sum of the Pss field of each type (anon, file, shmem).
+		For more details, see Documentation/filesystems/proc.txt
+		and the procfs man page.
 		Typical output looks like this:
 		00100000-ff709000 ---p 00000000 00:00 0		 [rollup]
+		Size:               1192 kB
+		KernelPageSize:        4 kB
+		MMUPageSize:           4 kB
 		Rss:		     884 kB
 		Pss:		     385 kB
+		Pss_Anon:	     301 kB
+		Pss_File:	      80 kB
+		Pss_Shmem:	       4 kB
 		Shared_Clean:	     696 kB
 		Shared_Dirty:	       0 kB
 		Private_Clean:	     120 kB
diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
index 66cad5c86171..e21c975d75f0 100644
--- a/Documentation/filesystems/proc.txt
+++ b/Documentation/filesystems/proc.txt
@@ -153,9 +153,11 @@ Table 1-1: Process specific entries in /proc
 		symbol the task is blocked in - or "0" if not blocked.
  pagemap	Page table
  stack		Report full stack trace, enable via CONFIG_STACKTRACE
- smaps		an extension based on maps, showing the memory consumption of
+ smaps		An extension based on maps, showing the memory consumption of
 		each mapping and flags associated with it
- numa_maps	an extension based on maps, showing the memory locality and
+ smaps_rollup	Accumulated smaps stats for all mappings of the process.  This
+		can be derived from smaps, but is faster and more convenient
+ numa_maps	An extension based on maps, showing the memory locality and
 		binding policy as well as mem usage (in pages) of each mapping.
@@ -365,7 +367,7 @@ Table 1-4: Contents of the stat files (as of 2.6.30-rc7)
   exit_code     the thread's exit_code in the form reported by the waitpid system call
-The /proc/PID/maps file containing the currently mapped memory regions and
+The /proc/PID/maps file contains the currently mapped memory regions and
 their access permissions.
 The format is:
@@ -416,11 +418,14 @@ is not associated with a file:
  or if empty, the mapping is anonymous.
 The /proc/PID/smaps is an extension based on maps, showing the memory
-consumption for each of the process's mappings. For each of mappings there
-is a series of lines such as the following:
+consumption for each of the process's mappings. For each mapping (aka Virtual
+Memory Area, or VMA) there is a series of lines such as the following:
 08048000-080bc000 r-xp 00000000 03:02 13130      /bin/bash
 Size:               1084 kB
+KernelPageSize:        4 kB
+MMUPageSize:           4 kB
 Rss:                 892 kB
 Pss:                 374 kB
 Shared_Clean:        892 kB
@@ -442,11 +447,14 @@ Locked:                0 kB
 THPeligible:           0
 VmFlags: rd ex mr mw me dw
-the first of these lines shows the same information as is displayed for the
-mapping in /proc/PID/maps.  The remaining lines show the size of the mapping
-(size), the amount of the mapping that is currently resident in RAM (RSS), the
-process' proportional share of this mapping (PSS), the number of clean and
-dirty private pages in the mapping.
+The first of these lines shows the same information as is displayed for the
+mapping in /proc/PID/maps.  Following lines show the size of the mapping
+(size); the size of each page allocated when backing a VMA (KernelPageSize),
+which is usually the same as the size in the page table entries; the page size
+used by the MMU when backing a VMA (in most cases, the same as KernelPageSize);
+the amount of the mapping that is currently resident in RAM (RSS); the
+process' proportional share of this mapping (PSS); and the number of clean and
+dirty shared and private pages in the mapping.
 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.
@@ -531,6 +539,19 @@ guarantees:
 2) If there is something at a given vaddr during the entirety of the
    life of the smaps/maps walk, there will be some output for it.
+The /proc/PID/smaps_rollup file includes the same fields as /proc/PID/smaps,
+but their values are the sums of the corresponding values for all mappings of
+the process.  Additionally, it contains these fields:
+They represent the proportional shares of anonymous, file, and shmem pages, as
+described for smaps above.  These fields are omitted in smaps since each
+mapping identifies the type (anon, file, or shmem) of all pages it contains.
+Thus all information in smaps_rollup can be derived from smaps, but at a
+significantly higher cost.
 The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG
 bits on both physical and virtual pages associated with a process, and the
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 01d4eb0e6bd1..00d110dcd6c2 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -417,17 +417,53 @@ struct mem_size_stats {
 	unsigned long shared_hugetlb;
 	unsigned long private_hugetlb;
 	u64 pss;
+	u64 pss_anon;
+	u64 pss_file;
+	u64 pss_shmem;
 	u64 pss_locked;
 	u64 swap_pss;
 	bool check_shmem_swap;
+static void smaps_page_accumulate(struct mem_size_stats *mss,
+		struct page *page, unsigned long size, unsigned long pss,
+		bool dirty, bool locked, bool private)
+	mss->pss += pss;
+	if (PageAnon(page))
+		mss->pss_anon += pss;
+	else if (PageSwapBacked(page))
+		mss->pss_shmem += pss;
+	else
+		mss->pss_file += pss;
+	if (locked)
+		mss->pss_locked += pss;
+	if (dirty || PageDirty(page)) {
+		if (private)
+			mss->private_dirty += size;
+		else
+			mss->shared_dirty += size;
+	} else {
+		if (private)
+			mss->private_clean += size;
+		else
+			mss->shared_clean += size;
+	}
 static void smaps_account(struct mem_size_stats *mss, struct page *page,
 		bool compound, bool young, bool dirty, bool locked)
 	int i, nr = compound ? 1 << compound_order(page) : 1;
 	unsigned long size = nr * PAGE_SIZE;
+	/*
+	 * First accumulate quantities that depend only on |size| and the type
+	 * of the compound page.
+	 */
 	if (PageAnon(page)) {
 		mss->anonymous += size;
 		if (!PageSwapBacked(page) && !dirty && !PageDirty(page))
@@ -440,42 +476,25 @@ static void smaps_account(struct mem_size_stats *mss, struct page *page,
 		mss->referenced += size;
+	 * Then accumulate quantities that may depend on sharing, or that may
+	 * differ page-by-page.
+	 *
 	 * page_count(page) == 1 guarantees the page is mapped exactly once.
 	 * If any subpage of the compound page mapped with PTE it would elevate
 	 * page_count().
 	if (page_count(page) == 1) {
-		if (dirty || PageDirty(page))
-			mss->private_dirty += size;
-		else
-			mss->private_clean += size;
-		mss->pss += (u64)size << PSS_SHIFT;
-		if (locked)
-			mss->pss_locked += (u64)size << PSS_SHIFT;
+		smaps_page_accumulate(mss, page, size, size << PSS_SHIFT, dirty,
+			locked, true);
 	for (i = 0; i < nr; i++, page++) {
 		int mapcount = page_mapcount(page);
-		unsigned long pss = (PAGE_SIZE << PSS_SHIFT);
-		if (mapcount >= 2) {
-			if (dirty || PageDirty(page))
-				mss->shared_dirty += PAGE_SIZE;
-			else
-				mss->shared_clean += PAGE_SIZE;
-			mss->pss += pss / mapcount;
-			if (locked)
-				mss->pss_locked += pss / mapcount;
-		} else {
-			if (dirty || PageDirty(page))
-				mss->private_dirty += PAGE_SIZE;
-			else
-				mss->private_clean += PAGE_SIZE;
-			mss->pss += pss;
-			if (locked)
-				mss->pss_locked += pss;
-		}
+		unsigned long pss = PAGE_SIZE << PSS_SHIFT;
+		if (mapcount >= 2)
+			pss /= mapcount;
+		smaps_page_accumulate(mss, page, PAGE_SIZE, pss, dirty, locked,
+				      mapcount < 2);
@@ -754,10 +773,23 @@ static void smap_gather_stats(struct vm_area_struct *vma,
 		seq_put_decimal_ull_width(m, str, (val) >> 10, 8)
 /* Show the contents common for smaps and smaps_rollup */
-static void __show_smap(struct seq_file *m, const struct mem_size_stats *mss)
+static void __show_smap(struct seq_file *m, const struct mem_size_stats *mss,
+	bool rollup_mode)
 	SEQ_PUT_DEC("Rss:            ", mss->resident);
 	SEQ_PUT_DEC(" kB\nPss:            ", mss->pss >> PSS_SHIFT);
+	if (rollup_mode) {
+		/*
+		 * These are meaningful only for smaps_rollup, otherwise two of
+		 * them are zero, and the other one is the same as Pss.
+		 */
+		SEQ_PUT_DEC(" kB\nPss_Anon:       ",
+			mss->pss_anon >> PSS_SHIFT);
+		SEQ_PUT_DEC(" kB\nPss_File:       ",
+			mss->pss_file >> PSS_SHIFT);
+		SEQ_PUT_DEC(" kB\nPss_Shmem:      ",
+			mss->pss_shmem >> PSS_SHIFT);
+	}
 	SEQ_PUT_DEC(" kB\nShared_Clean:   ", mss->shared_clean);
 	SEQ_PUT_DEC(" kB\nShared_Dirty:   ", mss->shared_dirty);
 	SEQ_PUT_DEC(" kB\nPrivate_Clean:  ", mss->private_clean);
@@ -794,7 +826,7 @@ static int show_smap(struct seq_file *m, void *v)
 	SEQ_PUT_DEC(" kB\nMMUPageSize:    ", vma_mmu_pagesize(vma));
 	seq_puts(m, " kB\n");
-	__show_smap(m, &mss);
+	__show_smap(m, &mss, false);
 	seq_printf(m, "THPeligible:    %d\n", transparent_hugepage_enabled(vma));
@@ -841,7 +873,7 @@ static int show_smaps_rollup(struct seq_file *m, void *v)
 	seq_pad(m, ' ');
 	seq_puts(m, "[rollup]\n");
-	__show_smap(m, &mss);
+	__show_smap(m, &mss, true);

                 reply index

Thread overview: [no followups] expand[flat|nested]  mbox.gz  Atom feed

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \ \ \ \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-mm Archive on

Archives are clonable:
	git clone --mirror linux-mm/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-mm linux-mm/ \
	public-inbox-index linux-mm

Example config snippet for mirrors

Newsgroup available over NNTP:

AGPL code for this site: git clone