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    Subject[RFC][PATCH v7 01/14] memcg: document cgroup dirty memory interfaces
    Date
    Document cgroup dirty memory interfaces and statistics.

    The implementation for these new interfaces routines comes in a series
    of following patches.

    Signed-off-by: Andrea Righi <arighi@develer.com>
    Signed-off-by: Greg Thelen <gthelen@google.com>
    Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
    Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>
    ---
    Changelog since v6:
    - Removed 'Inode writeback issue' now that memcg-writeback is implemented in
    the series.
    - Trivial reword of section 5.6 "dirty memory".

    Changelog since v4:
    - Minor rewording of '5.5 dirty memory' section.
    - Added '5.5.1 Inode writeback issue' section.

    Changelog since v3:
    - Described interactions with memory.use_hierarchy.
    - Added description of total_dirty, total_writeback, and total_nfs_unstable.

    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 | 70 ++++++++++++++++++++++++++++++++++++++
    1 files changed, 70 insertions(+), 0 deletions(-)

    diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
    index 43b9e46..15019a3 100644
    --- a/Documentation/cgroups/memory.txt
    +++ b/Documentation/cgroups/memory.txt
    @@ -395,6 +395,10 @@ soft_direct_steal- # of pages reclaimed in global hierarchical reclaim from
    direct reclaim
    soft_direct_scan- # of pages scanned in global hierarchical reclaim from
    direct reclaim
    +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
    @@ -420,6 +424,9 @@ total_soft_kswapd_steal - sum of all children's "soft_kswapd_steal"
    total_soft_kswapd_scan - sum of all children's "soft_kswapd_scan"
    total_soft_direct_steal - sum of all children's "soft_direct_steal"
    total_soft_direct_scan - sum of all children's "soft_direct_scan"
    +total_dirty - sum of all children's "dirty"
    +total_writeback - sum of all children's "writeback"
    +total_nfs_unstable - sum of all children's "nfs_unstable"
    total_inactive_anon - sum of all children's "inactive_anon"
    total_active_anon - sum of all children's "active_anon"
    total_inactive_file - sum of all children's "inactive_file"
    @@ -476,6 +483,69 @@ value for efficient access. (Of course, when necessary, it's synchronized.)
    If you want to know more exact memory usage, you should use RSS+CACHE(+SWAP)
    value in memory.stat(see 5.2).

    +5.6 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 throttled if they cross that limit. System-wide dirty limits are also
    +consulted. Dirty memory consumption is checked against both system-wide and
    +per-cgroup dirty limits.
    +
    +The interface is similar to the procfs interface: /proc/sys/vm/dirty_*. It is
    +possible to configure a limit to trigger throttling of a dirtier or queue
    +background writeback. 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 be throttled.
    + The default value is the system-wide dirty ratio, /proc/sys/vm/dirty_ratio.
    +
    +- memory.dirty_limit_in_bytes: the amount of dirty memory (expressed in bytes)
    + in the cgroup at which a process generating dirty pages will be throttled.
    + Suffix (k, K, m, M, g, or G) can be used to indicate that value is kilo, mega
    + or gigabytes. The default value is the system-wide dirty limit,
    + /proc/sys/vm/dirty_bytes.
    +
    + Note: memory.dirty_limit_in_bytes is the counterpart of memory.dirty_ratio.
    + Only one 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. The default value is the
    + system-wide background dirty ratio, /proc/sys/vm/dirty_background_ratio.
    +
    +- 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. The default value is the
    + system-wide dirty background limit, /proc/sys/vm/dirty_background_bytes.
    +
    + Note: memory.dirty_background_limit_in_bytes is the counterpart of
    + memory.dirty_background_ratio. Only one 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.
    +
    +When use_hierarchy=0, each cgroup has independent dirty memory usage and limits.
    +When use_hierarchy=1 the dirty limits of parent cgroups are also checked to
    +ensure that no dirty limit is exceeded.
    +
    6. Hierarchy support

    The memory controller supports a deep hierarchy and hierarchical accounting.
    --
    1.7.3.1


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