From: Daniel Colascione <dancol@xxxxxxxxxx>
Subject: 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@xxxxxxxxxx
Signed-off-by: Daniel Colascione <dancol@xxxxxxxxxx>
Cc: Tim Murray <timmurray@xxxxxxxxxx>
Cc: Joel Fernandes <joelaf@xxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Sonny Rao <sonnyrao@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/ABI/testing/procfs-smaps_rollup | 34 ++
fs/proc/base.c | 2
fs/proc/internal.h | 3
fs/proc/task_mmu.c | 196 ++++++++++------
4 files changed, 173 insertions(+), 62 deletions(-)
diff -puN /dev/null Documentation/ABI/testing/procfs-smaps_rollup
--- /dev/null
+++ a/Documentation/ABI/testing/procfs-smaps_rollup
@@ -0,0 +1,34 @@
+What: /proc/pid/smaps_rollup
+Date: August 2017
+Contact: Daniel Colascione <dancol@xxxxxxxxxx>
+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 -puN fs/proc/base.c~add-proc-pid-smaps_rollup fs/proc/base.c
--- a/fs/proc/base.c~add-proc-pid-smaps_rollup
+++ a/fs/proc/base.c
@@ -2931,6 +2931,7 @@ static const struct pid_entry tgid_base_
#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_s
#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 -puN fs/proc/internal.h~add-proc-pid-smaps_rollup fs/proc/internal.h
--- a/fs/proc/internal.h~add-proc-pid-smaps_rollup
+++ a/fs/proc/internal.h
@@ -269,10 +269,12 @@ extern int proc_remount(struct super_blo
/*
* 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
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 -puN fs/proc/task_mmu.c~add-proc-pid-smaps_rollup fs/proc/task_mmu.c
--- a/fs/proc/task_mmu.c~add-proc-pid-smaps_rollup
+++ a/fs/proc/task_mmu.c
@@ -253,6 +253,7 @@ static int proc_map_release(struct inode
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_pri
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
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_ma
#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_fi
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,
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,
/* mmap_sem is held in m_start */
walk_page_vma(vma, &smaps_walk);
+ if (vma->vm_flags & VM_LOCKED)
+ mss->pss_locked += mss->pss;
- 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) {
+ 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;
+ }
+
+ 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 *
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);
@@ -847,6 +912,13 @@ const struct file_operations proc_pid_sm
.read = seq_read,
.llseek = seq_lseek,
.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 = {
_
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