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author | Daniel Colascione <dancol@google.com> | 2017-09-06 16:25:08 -0700 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2017-09-06 17:27:30 -0700 |
commit | 493b0e9d945fa9dfe96be93ae41b4ca4b6fdb317 (patch) | |
tree | c994839f490d27e9bff0715b90a5c8a124b331ad /fs/proc/task_mmu.c | |
parent | c79b57e462b5d2f47afa5f175cf1828f16e18612 (diff) | |
download | linux-stable-493b0e9d945fa9dfe96be93ae41b4ca4b6fdb317.tar.gz linux-stable-493b0e9d945fa9dfe96be93ae41b4ca4b6fdb317.tar.bz2 linux-stable-493b0e9d945fa9dfe96be93ae41b4ca4b6fdb317.zip |
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>
Diffstat (limited to 'fs/proc/task_mmu.c')
-rw-r--r-- | fs/proc/task_mmu.c | 196 |
1 files changed, 134 insertions, 62 deletions
diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c index fe8f3265e877..b2330aedc63f 100644 --- 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, |