• V
    memcg: add page_cgroup_ino helper · 2fc04524
    Vladimir Davydov 提交于
    This patchset introduces a new user API for tracking user memory pages
    that have not been used for a given period of time.  The purpose of this
    is to provide the userspace with the means of tracking a workload's
    working set, i.e.  the set of pages that are actively used by the
    workload.  Knowing the working set size can be useful for partitioning the
    system more efficiently, e.g.  by tuning memory cgroup limits
    appropriately, or for job placement within a compute cluster.
    
    ==== USE CASES ====
    
    The unified cgroup hierarchy has memory.low and memory.high knobs, which
    are defined as the low and high boundaries for the workload working set
    size.  However, the working set size of a workload may be unknown or
    change in time.  With this patch set, one can periodically estimate the
    amount of memory unused by each cgroup and tune their memory.low and
    memory.high parameters accordingly, therefore optimizing the overall
    memory utilization.
    
    Another use case is balancing workloads within a compute cluster.  Knowing
    how much memory is not really used by a workload unit may help take a more
    optimal decision when considering migrating the unit to another node
    within the cluster.
    
    Also, as noted by Minchan, this would be useful for per-process reclaim
    (https://lwn.net/Articles/545668/). With idle tracking, we could reclaim idle
    pages only by smart user memory manager.
    
    ==== USER API ====
    
    The user API consists of two new files:
    
     * /sys/kernel/mm/page_idle/bitmap.  This file implements a bitmap where each
       bit corresponds to a page, indexed by PFN. When the bit is set, the
       corresponding page is idle. A page is considered idle if it has not been
       accessed since it was marked idle. To mark a page idle one should set the
       bit corresponding to the page by writing to the file. A value written to the
       file is OR-ed with the current bitmap value. Only user memory pages can be
       marked idle, for other page types input is silently ignored. Writing to this
       file beyond max PFN results in the ENXIO error. Only available when
       CONFIG_IDLE_PAGE_TRACKING is set.
    
       This file can be used to estimate the amount of pages that are not
       used by a particular workload as follows:
    
       1. mark all pages of interest idle by setting corresponding bits in the
          /sys/kernel/mm/page_idle/bitmap
       2. wait until the workload accesses its working set
       3. read /sys/kernel/mm/page_idle/bitmap and count the number of bits set
    
     * /proc/kpagecgroup.  This file contains a 64-bit inode number of the
       memory cgroup each page is charged to, indexed by PFN. Only available when
       CONFIG_MEMCG is set.
    
       This file can be used to find all pages (including unmapped file pages)
       accounted to a particular cgroup. Using /sys/kernel/mm/page_idle/bitmap, one
       can then estimate the cgroup working set size.
    
    For an example of using these files for estimating the amount of unused
    memory pages per each memory cgroup, please see the script attached
    below.
    
    ==== REASONING ====
    
    The reason to introduce the new user API instead of using
    /proc/PID/{clear_refs,smaps} is that the latter has two serious
    drawbacks:
    
     - it does not count unmapped file pages
     - it affects the reclaimer logic
    
    The new API attempts to overcome them both. For more details on how it
    is achieved, please see the comment to patch 6.
    
    ==== PATCHSET STRUCTURE ====
    
    The patch set is organized as follows:
    
     - patch 1 adds page_cgroup_ino() helper for the sake of
       /proc/kpagecgroup and patches 2-3 do related cleanup
     - patch 4 adds /proc/kpagecgroup, which reports cgroup ino each page is
       charged to
     - patch 5 introduces a new mmu notifier callback, clear_young, which is
       a lightweight version of clear_flush_young; it is used in patch 6
     - patch 6 implements the idle page tracking feature, including the
       userspace API, /sys/kernel/mm/page_idle/bitmap
     - patch 7 exports idle flag via /proc/kpageflags
    
    ==== SIMILAR WORKS ====
    
    Originally, the patch for tracking idle memory was proposed back in 2011
    by Michel Lespinasse (see http://lwn.net/Articles/459269/).  The main
    difference between Michel's patch and this one is that Michel implemented
    a kernel space daemon for estimating idle memory size per cgroup while
    this patch only provides the userspace with the minimal API for doing the
    job, leaving the rest up to the userspace.  However, they both share the
    same idea of Idle/Young page flags to avoid affecting the reclaimer logic.
    
    ==== PERFORMANCE EVALUATION ====
    
    SPECjvm2008 (https://www.spec.org/jvm2008/) was used to evaluate the
    performance impact introduced by this patch set.  Three runs were carried
    out:
    
     - base: kernel without the patch
     - patched: patched kernel, the feature is not used
     - patched-active: patched kernel, 1 minute-period daemon is used for
       tracking idle memory
    
    For tracking idle memory, idlememstat utility was used:
    https://github.com/locker/idlememstat
    
    testcase            base            patched        patched-active
    
    compiler       537.40 ( 0.00)%   532.26 (-0.96)%   538.31 ( 0.17)%
    compress       305.47 ( 0.00)%   301.08 (-1.44)%   300.71 (-1.56)%
    crypto         284.32 ( 0.00)%   282.21 (-0.74)%   284.87 ( 0.19)%
    derby          411.05 ( 0.00)%   413.44 ( 0.58)%   412.07 ( 0.25)%
    mpegaudio      189.96 ( 0.00)%   190.87 ( 0.48)%   189.42 (-0.28)%
    scimark.large   46.85 ( 0.00)%    46.41 (-0.94)%    47.83 ( 2.09)%
    scimark.small  412.91 ( 0.00)%   415.41 ( 0.61)%   421.17 ( 2.00)%
    serial         204.23 ( 0.00)%   213.46 ( 4.52)%   203.17 (-0.52)%
    startup         36.76 ( 0.00)%    35.49 (-3.45)%    35.64 (-3.05)%
    sunflow        115.34 ( 0.00)%   115.08 (-0.23)%   117.37 ( 1.76)%
    xml            620.55 ( 0.00)%   619.95 (-0.10)%   620.39 (-0.03)%
    
    composite      211.50 ( 0.00)%   211.15 (-0.17)%   211.67 ( 0.08)%
    
    time idlememstat:
    
    17.20user 65.16system 2:15:23elapsed 1%CPU (0avgtext+0avgdata 8476maxresident)k
    448inputs+40outputs (1major+36052minor)pagefaults 0swaps
    
    ==== SCRIPT FOR COUNTING IDLE PAGES PER CGROUP ====
    #! /usr/bin/python
    #
    
    import os
    import stat
    import errno
    import struct
    
    CGROUP_MOUNT = "/sys/fs/cgroup/memory"
    BUFSIZE = 8 * 1024  # must be multiple of 8
    
    def get_hugepage_size():
        with open("/proc/meminfo", "r") as f:
            for s in f:
                k, v = s.split(":")
                if k == "Hugepagesize":
                    return int(v.split()[0]) * 1024
    
    PAGE_SIZE = os.sysconf("SC_PAGE_SIZE")
    HUGEPAGE_SIZE = get_hugepage_size()
    
    def set_idle():
        f = open("/sys/kernel/mm/page_idle/bitmap", "wb", BUFSIZE)
        while True:
            try:
                f.write(struct.pack("Q", pow(2, 64) - 1))
            except IOError as err:
                if err.errno == errno.ENXIO:
                    break
                raise
        f.close()
    
    def count_idle():
        f_flags = open("/proc/kpageflags", "rb", BUFSIZE)
        f_cgroup = open("/proc/kpagecgroup", "rb", BUFSIZE)
    
        with open("/sys/kernel/mm/page_idle/bitmap", "rb", BUFSIZE) as f:
            while f.read(BUFSIZE): pass  # update idle flag
    
        idlememsz = {}
        while True:
            s1, s2 = f_flags.read(8), f_cgroup.read(8)
            if not s1 or not s2:
                break
    
            flags, = struct.unpack('Q', s1)
            cgino, = struct.unpack('Q', s2)
    
            unevictable = (flags >> 18) & 1
            huge = (flags >> 22) & 1
            idle = (flags >> 25) & 1
    
            if idle and not unevictable:
                idlememsz[cgino] = idlememsz.get(cgino, 0) + \
                    (HUGEPAGE_SIZE if huge else PAGE_SIZE)
    
        f_flags.close()
        f_cgroup.close()
        return idlememsz
    
    if __name__ == "__main__":
        print "Setting the idle flag for each page..."
        set_idle()
    
        raw_input("Wait until the workload accesses its working set, "
                  "then press Enter")
    
        print "Counting idle pages..."
        idlememsz = count_idle()
    
        for dir, subdirs, files in os.walk(CGROUP_MOUNT):
            ino = os.stat(dir)[stat.ST_INO]
            print dir + ": " + str(idlememsz.get(ino, 0) / 1024) + " kB"
    ==== END SCRIPT ====
    
    This patch (of 8):
    
    Add page_cgroup_ino() helper to memcg.
    
    This function returns the inode number of the closest online ancestor of
    the memory cgroup a page is charged to.  It is required for exporting
    information about which page is charged to which cgroup to userspace,
    which will be introduced by a following patch.
    Signed-off-by: NVladimir Davydov <vdavydov@parallels.com>
    Reviewed-by: NAndres Lagar-Cavilla <andreslc@google.com>
    Cc: Minchan Kim <minchan@kernel.org>
    Cc: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
    Cc: Johannes Weiner <hannes@cmpxchg.org>
    Cc: Michal Hocko <mhocko@suse.cz>
    Cc: Greg Thelen <gthelen@google.com>
    Cc: Michel Lespinasse <walken@google.com>
    Cc: David Rientjes <rientjes@google.com>
    Cc: Pavel Emelyanov <xemul@parallels.com>
    Cc: Cyrill Gorcunov <gorcunov@openvz.org>
    Cc: Jonathan Corbet <corbet@lwn.net>
    Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
    2fc04524
memcontrol.c 147.0 KB