mm: add /proc/pid/smaps_rollup

/proc/pid/smaps_rollup is a new proc file that improves the performance
of user programs that determine aggregate memory statistics (e.g., total
PSS) of a process.

Android regularly "samples" the memory usage of various processes in
order to balance its memory pool sizes.  This sampling process involves
opening /proc/pid/smaps and summing certain fields.  For very large
processes, sampling memory use this way can take several hundred
milliseconds, due mostly to the overhead of the seq_printf calls in
task_mmu.c.

smaps_rollup improves the situation.  It contains most of the fields of
/proc/pid/smaps, but instead of a set of fields for each VMA,
smaps_rollup instead contains one synthetic smaps-format entry
representing the whole process.  In the single smaps_rollup synthetic
entry, each field is the summation of the corresponding field in all of
the real-smaps VMAs.  Using a common format for smaps_rollup and smaps
allows userspace parsers to repurpose parsers meant for use with
non-rollup smaps for smaps_rollup, and it allows userspace to switch
between smaps_rollup and smaps at runtime (say, based on the
availability of smaps_rollup in a given kernel) with minimal fuss.

By using smaps_rollup instead of smaps, a caller can avoid the
significant overhead of formatting, reading, and parsing each of a large
process's potentially very numerous memory mappings.  For sampling
system_server's PSS in Android, we measured a 12x speedup, representing
a savings of several hundred milliseconds.

One alternative to a new per-process proc file would have been including
PSS information in /proc/pid/status.  We considered this option but
thought that PSS would be too expensive (by a few orders of magnitude)
to collect relative to what's already emitted as part of
/proc/pid/status, and slowing every user of /proc/pid/status for the
sake of readers that happen to want PSS feels wrong.

The code itself works by reusing the existing VMA-walking framework we
use for regular smaps generation and keeping the mem_size_stats
structure around between VMA walks instead of using a fresh one for each
VMA.  In this way, summation happens automatically.  We let seq_file
walk over the VMAs just as it does for regular smaps and just emit
nothing to the seq_file until we hit the last VMA.

Benchmarks:

    using smaps:
    iterations:1000 pid:1163 pss:220023808
    0m29.46s real 0m08.28s user 0m20.98s system

    using smaps_rollup:
    iterations:1000 pid:1163 pss:220702720
    0m04.39s real 0m00.03s user 0m04.31s system

We're using the PSS samples we collect asynchronously for
system-management tasks like fine-tuning oom_adj_score, memory use
tracking for debugging, application-level memory-use attribution, and
deciding whether we want to kill large processes during system idle
maintenance windows.  Android has been using PSS for these purposes for
a long time; as the average process VMA count has increased and and
devices become more efficiency-conscious, PSS-collection inefficiency
has started to matter more.  IMHO, it'd be a lot safer to optimize the
existing PSS-collection model, which has been fine-tuned over the years,
instead of changing the memory tracking approach entirely to work around
smaps-generation inefficiency.

Tim said:

: There are two main reasons why Android gathers PSS information:
:
: 1. Android devices can show the user the amount of memory used per
:    application via the settings app.  This is a less important use case.
:
: 2. We log PSS to help identify leaks in applications.  We have found
:    an enormous number of bugs (in the Android platform, in Google's own
:    apps, and in third-party applications) using this data.
:
: To do this, system_server (the main process in Android userspace) will
: sample the PSS of a process three seconds after it changes state (for
: example, app is launched and becomes the foreground application) and about
: every ten minutes after that.  The net result is that PSS collection is
: regularly running on at least one process in the system (usually a few
: times a minute while the screen is on, less when screen is off due to
: suspend).  PSS of a process is an incredibly useful stat to track, and we
: aren't going to get rid of it.  We've looked at some very hacky approaches
: using RSS ("take the RSS of the target process, subtract the RSS of the
: zygote process that is the parent of all Android apps") to reduce the
: accounting time, but it regularly overestimated the memory used by 20+
: percent.  Accordingly, I don't think that there's a good alternative to
: using PSS.
:
: We started looking into PSS collection performance after we noticed random
: frequency spikes while a phone's screen was off; occasionally, one of the
: CPU clusters would ramp to a high frequency because there was 200-300ms of
: constant CPU work from a single thread in the main Android userspace
: process.  The work causing the spike (which is reasonable governor
: behavior given the amount of CPU time needed) was always PSS collection.
: As a result, Android is burning more power than we should be on PSS
: collection.
:
: The other issue (and why I'm less sure about improving smaps as a
: long-term solution) is that the number of VMAs per process has increased
: significantly from release to release.  After trying to figure out why we
: were seeing these 200-300ms PSS collection times on Android O but had not
: noticed it in previous versions, we found that the number of VMAs in the
: main system process increased by 50% from Android N to Android O (from
: ~1800 to ~2700) and varying increases in every userspace process.  Android
: M to N also had an increase in the number of VMAs, although not as much.
: I'm not sure why this is increasing so much over time, but thinking about
: ASLR and ways to make ASLR better, I expect that this will continue to
: increase going forward.  I would not be surprised if we hit 5000 VMAs on
: the main Android process (system_server) by 2020.
:
: If we assume that the number of VMAs is going to increase over time, then
: doing anything we can do to reduce the overhead of each VMA during PSS
: collection seems like the right way to go, and that means outputting an
: aggregate statistic (to avoid whatever overhead there is per line in
: writing smaps and in reading each line from userspace).

Link: http://lkml.kernel.org/r/20170812022148.178293-1-dancol@google.com
Signed-off-by: Daniel Colascione <dancol@google.com>
Cc: Tim Murray <timmurray@google.com>
Cc: Joel Fernandes <joelaf@google.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Sonny Rao <sonnyrao@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/Documentation/ABI/testing/procfs-smaps_rollup b/Documentation/ABI/testing/procfs-smaps_rollup
new file mode 100644 (file)
index 0000000..0a54ed0
--- /dev/null
+++ b/Documentation/ABI/testing/procfs-smaps_rollup
@@ -0,0 +1,31 @@
+What:          /proc/pid/smaps_rollup
+Date:          August 2017
+Contact:       Daniel Colascione <dancol@google.com>
+Description:
+               This file provides pre-summed memory information for a
+               process.  The format is 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.
+
+               Typical output looks like this:
+
+               00100000-ff709000 ---p 00000000 00:00 0          [rollup]
+               Rss:                 884 kB
+               Pss:                 385 kB
+               Shared_Clean:        696 kB
+               Shared_Dirty:          0 kB
+               Private_Clean:       120 kB
+               Private_Dirty:        68 kB
+               Referenced:          884 kB
+               Anonymous:            68 kB
+               LazyFree:              0 kB
+               AnonHugePages:         0 kB
+               ShmemPmdMapped:        0 kB
+               Shared_Hugetlb:        0 kB
+               Private_Hugetlb:       0 kB
+               Swap:                  0 kB
+               SwapPss:               0 kB
+               Locked:              385 kB

diff --git a/fs/proc/base.c b/fs/proc/base.c
index 98fd8f6df85122beda8066b734e23aabe3e7b306..e5d89a0d0b8a7bceb29dae702436a572dc041336 100644 (file)
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2931,6 +2931,7 @@ static const struct pid_entry tgid_base_stuff[] = {
 #ifdef CONFIG_PROC_PAGE_MONITOR
        REG("clear_refs", S_IWUSR, proc_clear_refs_operations),
        REG("smaps",      S_IRUGO, proc_pid_smaps_operations),
+       REG("smaps_rollup", S_IRUGO, proc_pid_smaps_rollup_operations),
        REG("pagemap",    S_IRUSR, proc_pagemap_operations),
 #endif
 #ifdef CONFIG_SECURITY
@@ -3324,6 +3325,7 @@ static const struct pid_entry tid_base_stuff[] = {
 #ifdef CONFIG_PROC_PAGE_MONITOR
        REG("clear_refs", S_IWUSR, proc_clear_refs_operations),
        REG("smaps",     S_IRUGO, proc_tid_smaps_operations),
+       REG("smaps_rollup", S_IRUGO, proc_pid_smaps_rollup_operations),
        REG("pagemap",    S_IRUSR, proc_pagemap_operations),
 #endif
 #ifdef CONFIG_SECURITY

diff --git a/fs/proc/internal.h b/fs/proc/internal.h
index aa2b8907163086daf83034a3dcf54b011d794fe9..2cbfcd32e884478c9806c64986874bf49bd8ed8e 100644 (file)
--- a/fs/proc/internal.h
+++ b/fs/proc/internal.h
@@ -269,10 +269,12 @@ extern int proc_remount(struct super_block *, int *, char *);
 /*
  * task_[no]mmu.c
  */
+struct mem_size_stats;
 struct proc_maps_private {
        struct inode *inode;
        struct task_struct *task;
        struct mm_struct *mm;
+       struct mem_size_stats *rollup;
 #ifdef CONFIG_MMU
        struct vm_area_struct *tail_vma;
 #endif
@@ -288,6 +290,7 @@ extern const struct file_operations proc_tid_maps_operations;
 extern const struct file_operations proc_pid_numa_maps_operations;
 extern const struct file_operations proc_tid_numa_maps_operations;
 extern const struct file_operations proc_pid_smaps_operations;
+extern const struct file_operations proc_pid_smaps_rollup_operations;
 extern const struct file_operations proc_tid_smaps_operations;
 extern const struct file_operations proc_clear_refs_operations;
 extern const struct file_operations proc_pagemap_operations;

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index fe8f3265e8779ac18a5694ef600c024f9e88f281..b2330aedc63f01ef36988295a655899be74ffb2a 100644 (file)
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -253,6 +253,7 @@ static int proc_map_release(struct inode *inode, struct file *file)
        if (priv->mm)
                mmdrop(priv->mm);
 
+       kfree(priv->rollup);
        return seq_release_private(inode, file);
 }
 
@@ -279,6 +280,23 @@ static int is_stack(struct proc_maps_private *priv,
                vma->vm_end >= vma->vm_mm->start_stack;
 }
 
+static void show_vma_header_prefix(struct seq_file *m,
+                                  unsigned long start, unsigned long end,
+                                  vm_flags_t flags, unsigned long long pgoff,
+                                  dev_t dev, unsigned long ino)
+{
+       seq_setwidth(m, 25 + sizeof(void *) * 6 - 1);
+       seq_printf(m, "%08lx-%08lx %c%c%c%c %08llx %02x:%02x %lu ",
+                  start,
+                  end,
+                  flags & VM_READ ? 'r' : '-',
+                  flags & VM_WRITE ? 'w' : '-',
+                  flags & VM_EXEC ? 'x' : '-',
+                  flags & VM_MAYSHARE ? 's' : 'p',
+                  pgoff,
+                  MAJOR(dev), MINOR(dev), ino);
+}
+
 static void
 show_map_vma(struct seq_file *m, struct vm_area_struct *vma, int is_pid)
 {
@@ -301,17 +319,7 @@ show_map_vma(struct seq_file *m, struct vm_area_struct *vma, int is_pid)
 
        start = vma->vm_start;
        end = vma->vm_end;
-
-       seq_setwidth(m, 25 + sizeof(void *) * 6 - 1);
-       seq_printf(m, "%08lx-%08lx %c%c%c%c %08llx %02x:%02x %lu ",
-                       start,
-                       end,
-                       flags & VM_READ ? 'r' : '-',
-                       flags & VM_WRITE ? 'w' : '-',
-                       flags & VM_EXEC ? 'x' : '-',
-                       flags & VM_MAYSHARE ? 's' : 'p',
-                       pgoff,
-                       MAJOR(dev), MINOR(dev), ino);
+       show_vma_header_prefix(m, start, end, flags, pgoff, dev, ino);
 
        /*
         * Print the dentry name for named mappings, and a
@@ -430,6 +438,7 @@ const struct file_operations proc_tid_maps_operations = {
 
 #ifdef CONFIG_PROC_PAGE_MONITOR
 struct mem_size_stats {
+       bool first;
        unsigned long resident;
        unsigned long shared_clean;
        unsigned long shared_dirty;
@@ -443,7 +452,9 @@ struct mem_size_stats {
        unsigned long swap;
        unsigned long shared_hugetlb;
        unsigned long private_hugetlb;
+       unsigned long first_vma_start;
        u64 pss;
+       u64 pss_locked;
        u64 swap_pss;
        bool check_shmem_swap;
 };
@@ -719,18 +730,36 @@ void __weak arch_show_smap(struct seq_file *m, struct vm_area_struct *vma)
 
 static int show_smap(struct seq_file *m, void *v, int is_pid)
 {
+       struct proc_maps_private *priv = m->private;
        struct vm_area_struct *vma = v;
-       struct mem_size_stats mss;
+       struct mem_size_stats mss_stack;
+       struct mem_size_stats *mss;
        struct mm_walk smaps_walk = {
                .pmd_entry = smaps_pte_range,
 #ifdef CONFIG_HUGETLB_PAGE
                .hugetlb_entry = smaps_hugetlb_range,
 #endif
                .mm = vma->vm_mm,
-               .private = &mss,
        };
+       int ret = 0;
+       bool rollup_mode;
+       bool last_vma;
+
+       if (priv->rollup) {
+               rollup_mode = true;
+               mss = priv->rollup;
+               if (mss->first) {
+                       mss->first_vma_start = vma->vm_start;
+                       mss->first = false;
+               }
+               last_vma = !m_next_vma(priv, vma);
+       } else {
+               rollup_mode = false;
+               memset(&mss_stack, 0, sizeof(mss_stack));
+               mss = &mss_stack;
+       }
 
-       memset(&mss, 0, sizeof mss);
+       smaps_walk.private = mss;
 
 #ifdef CONFIG_SHMEM
        if (vma->vm_file && shmem_mapping(vma->vm_file->f_mapping)) {
@@ -748,9 +777,9 @@ static int show_smap(struct seq_file *m, void *v, int is_pid)
 
                if (!shmem_swapped || (vma->vm_flags & VM_SHARED) ||
                                        !(vma->vm_flags & VM_WRITE)) {
-                       mss.swap = shmem_swapped;
+                       mss->swap = shmem_swapped;
                } else {
-                       mss.check_shmem_swap = true;
+                       mss->check_shmem_swap = true;
                        smaps_walk.pte_hole = smaps_pte_hole;
                }
        }
@@ -758,54 +787,71 @@ static int show_smap(struct seq_file *m, void *v, int is_pid)
 
        /* mmap_sem is held in m_start */
        walk_page_vma(vma, &smaps_walk);
+       if (vma->vm_flags & VM_LOCKED)
+               mss->pss_locked += mss->pss;
+
+       if (!rollup_mode) {
+               show_map_vma(m, vma, is_pid);
+       } else if (last_vma) {
+               show_vma_header_prefix(
+                       m, mss->first_vma_start, vma->vm_end, 0, 0, 0, 0);
+               seq_pad(m, ' ');
+               seq_puts(m, "[rollup]\n");
+       } else {
+               ret = SEQ_SKIP;
+       }
 
-       show_map_vma(m, vma, is_pid);
-
-       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"
-                  "Private_Dirty:  %8lu kB\n"
-                  "Referenced:     %8lu kB\n"
-                  "Anonymous:      %8lu kB\n"
-                  "LazyFree:       %8lu kB\n"
-                  "AnonHugePages:  %8lu kB\n"
-                  "ShmemPmdMapped: %8lu kB\n"
-                  "Shared_Hugetlb: %8lu kB\n"
-                  "Private_Hugetlb: %7lu kB\n"
-                  "Swap:           %8lu kB\n"
-                  "SwapPss:        %8lu kB\n"
-                  "KernelPageSize: %8lu kB\n"
-                  "MMUPageSize:    %8lu kB\n"
-                  "Locked:         %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,
-                  mss.private_dirty >> 10,
-                  mss.referenced >> 10,
-                  mss.anonymous >> 10,
-                  mss.lazyfree >> 10,
-                  mss.anonymous_thp >> 10,
-                  mss.shmem_thp >> 10,
-                  mss.shared_hugetlb >> 10,
-                  mss.private_hugetlb >> 10,
-                  mss.swap >> 10,
-                  (unsigned long)(mss.swap_pss >> (10 + PSS_SHIFT)),
-                  vma_kernel_pagesize(vma) >> 10,
-                  vma_mmu_pagesize(vma) >> 10,
-                  (vma->vm_flags & VM_LOCKED) ?
-                       (unsigned long)(mss.pss >> (10 + PSS_SHIFT)) : 0);
-
-       arch_show_smap(m, vma);
-       show_smap_vma_flags(m, vma);
+       if (!rollup_mode)
+               seq_printf(m,
+                          "Size:           %8lu kB\n"
+                          "KernelPageSize: %8lu kB\n"
+                          "MMUPageSize:    %8lu kB\n",
+                          (vma->vm_end - vma->vm_start) >> 10,
+                          vma_kernel_pagesize(vma) >> 10,
+                          vma_mmu_pagesize(vma) >> 10);
+
+
+       if (!rollup_mode || last_vma)
+               seq_printf(m,
+                          "Rss:            %8lu kB\n"
+                          "Pss:            %8lu kB\n"
+                          "Shared_Clean:   %8lu kB\n"
+                          "Shared_Dirty:   %8lu kB\n"
+                          "Private_Clean:  %8lu kB\n"
+                          "Private_Dirty:  %8lu kB\n"
+                          "Referenced:     %8lu kB\n"
+                          "Anonymous:      %8lu kB\n"
+                          "LazyFree:       %8lu kB\n"
+                          "AnonHugePages:  %8lu kB\n"
+                          "ShmemPmdMapped: %8lu kB\n"
+                          "Shared_Hugetlb: %8lu kB\n"
+                          "Private_Hugetlb: %7lu kB\n"
+                          "Swap:           %8lu kB\n"
+                          "SwapPss:        %8lu kB\n"
+                          "Locked:         %8lu kB\n",
+                          mss->resident >> 10,
+                          (unsigned long)(mss->pss >> (10 + PSS_SHIFT)),
+                          mss->shared_clean  >> 10,
+                          mss->shared_dirty  >> 10,
+                          mss->private_clean >> 10,
+                          mss->private_dirty >> 10,
+                          mss->referenced >> 10,
+                          mss->anonymous >> 10,
+                          mss->lazyfree >> 10,
+                          mss->anonymous_thp >> 10,
+                          mss->shmem_thp >> 10,
+                          mss->shared_hugetlb >> 10,
+                          mss->private_hugetlb >> 10,
+                          mss->swap >> 10,
+                          (unsigned long)(mss->swap_pss >> (10 + PSS_SHIFT)),
+                          (unsigned long)(mss->pss >> (10 + PSS_SHIFT)));
+
+       if (!rollup_mode) {
+               arch_show_smap(m, vma);
+               show_smap_vma_flags(m, vma);
+       }
        m_cache_vma(m, vma);
-       return 0;
+       return ret;
 }
 
 static int show_pid_smap(struct seq_file *m, void *v)
@@ -837,6 +883,25 @@ static int pid_smaps_open(struct inode *inode, struct file *file)
        return do_maps_open(inode, file, &proc_pid_smaps_op);
 }
 
+static int pid_smaps_rollup_open(struct inode *inode, struct file *file)
+{
+       struct seq_file *seq;
+       struct proc_maps_private *priv;
+       int ret = do_maps_open(inode, file, &proc_pid_smaps_op);
+
+       if (ret < 0)
+               return ret;
+       seq = file->private_data;
+       priv = seq->private;
+       priv->rollup = kzalloc(sizeof(*priv->rollup), GFP_KERNEL);
+       if (!priv->rollup) {
+               proc_map_release(inode, file);
+               return -ENOMEM;
+       }
+       priv->rollup->first = true;
+       return 0;
+}
+
 static int tid_smaps_open(struct inode *inode, struct file *file)
 {
        return do_maps_open(inode, file, &proc_tid_smaps_op);
@@ -849,6 +914,13 @@ const struct file_operations proc_pid_smaps_operations = {
        .release        = proc_map_release,
 };
 
+const struct file_operations proc_pid_smaps_rollup_operations = {
+       .open           = pid_smaps_rollup_open,
+       .read           = seq_read,
+       .llseek         = seq_lseek,
+       .release        = proc_map_release,
+};
+
 const struct file_operations proc_tid_smaps_operations = {
        .open           = tid_smaps_open,
        .read           = seq_read,