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    Subject[PATCH v3 02/11] memcg: document cgroup dirty memory interfaces
    Date
    Document cgroup dirty memory interfaces and statistics.

    Signed-off-by: Andrea Righi <arighi@develer.com>
    Signed-off-by: Greg Thelen <gthelen@google.com>
    ---

    Changelog since v1:
    - Renamed "nfs"/"total_nfs" to "nfs_unstable"/"total_nfs_unstable" in per cgroup
    memory.stat to match /proc/meminfo.

    - Allow [kKmMgG] suffixes for newly created dirty limit value cgroupfs files.

    - Describe a situation where a cgroup can exceed its dirty limit.

    Documentation/cgroups/memory.txt | 60 ++++++++++++++++++++++++++++++++++++++
    1 files changed, 60 insertions(+), 0 deletions(-)

    diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
    index 7781857..02bbd6f 100644
    --- a/Documentation/cgroups/memory.txt
    +++ b/Documentation/cgroups/memory.txt
    @@ -385,6 +385,10 @@ mapped_file - # of bytes of mapped file (includes tmpfs/shmem)
    pgpgin - # of pages paged in (equivalent to # of charging events).
    pgpgout - # of pages paged out (equivalent to # of uncharging events).
    swap - # of bytes of swap usage
    +dirty - # of bytes that are waiting to get written back to the disk.
    +writeback - # of bytes that are actively being written back to the disk.
    +nfs_unstable - # of bytes sent to the NFS server, but not yet committed to
    + the actual storage.
    inactive_anon - # of bytes of anonymous memory and swap cache memory on
    LRU list.
    active_anon - # of bytes of anonymous and swap cache memory on active
    @@ -453,6 +457,62 @@ memory under it will be reclaimed.
    You can reset failcnt by writing 0 to failcnt file.
    # echo 0 > .../memory.failcnt

    +5.5 dirty memory
    +
    +Control the maximum amount of dirty pages a cgroup can have at any given time.
    +
    +Limiting dirty memory is like fixing the max amount of dirty (hard to reclaim)
    +page cache used by a cgroup. So, in case of multiple cgroup writers, they will
    +not be able to consume more than their designated share of dirty pages and will
    +be forced to perform write-out if they cross that limit.
    +
    +The interface is equivalent to the procfs interface: /proc/sys/vm/dirty_*. It
    +is possible to configure a limit to trigger both a direct writeback or a
    +background writeback performed by per-bdi flusher threads. The root cgroup
    +memory.dirty_* control files are read-only and match the contents of
    +the /proc/sys/vm/dirty_* files.
    +
    +Per-cgroup dirty limits can be set using the following files in the cgroupfs:
    +
    +- memory.dirty_ratio: the amount of dirty memory (expressed as a percentage of
    + cgroup memory) at which a process generating dirty pages will itself start
    + writing out dirty data.
    +
    +- memory.dirty_limit_in_bytes: the amount of dirty memory (expressed in bytes)
    + in the cgroup at which a process generating dirty pages will start itself
    + writing out dirty data. Suffix (k, K, m, M, g, or G) can be used to indicate
    + that value is kilo, mega or gigabytes.
    +
    + Note: memory.dirty_limit_in_bytes is the counterpart of memory.dirty_ratio.
    + Only one of them may be specified at a time. When one is written it is
    + immediately taken into account to evaluate the dirty memory limits and the
    + other appears as 0 when read.
    +
    +- memory.dirty_background_ratio: the amount of dirty memory of the cgroup
    + (expressed as a percentage of cgroup memory) at which background writeback
    + kernel threads will start writing out dirty data.
    +
    +- memory.dirty_background_limit_in_bytes: the amount of dirty memory (expressed
    + in bytes) in the cgroup at which background writeback kernel threads will
    + start writing out dirty data. Suffix (k, K, m, M, g, or G) can be used to
    + indicate that value is kilo, mega or gigabytes.
    +
    + Note: memory.dirty_background_limit_in_bytes is the counterpart of
    + memory.dirty_background_ratio. Only one of them may be specified at a time.
    + When one is written it is immediately taken into account to evaluate the dirty
    + memory limits and the other appears as 0 when read.
    +
    +A cgroup may contain more dirty memory than its dirty limit. This is possible
    +because of the principle that the first cgroup to touch a page is charged for
    +it. Subsequent page counting events (dirty, writeback, nfs_unstable) are also
    +counted to the originally charged cgroup.
    +
    +Example: If page is allocated by a cgroup A task, then the page is charged to
    +cgroup A. If the page is later dirtied by a task in cgroup B, then the cgroup A
    +dirty count will be incremented. If cgroup A is over its dirty limit but cgroup
    +B is not, then dirtying a cgroup A page from a cgroup B task may push cgroup A
    +over its dirty limit without throttling the dirtying cgroup B task.
    +
    6. Hierarchy support

    The memory controller supports a deep hierarchy and hierarchical accounting.
    --
    1.7.1


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