lkml.org 
[lkml]   [2010]   [Oct]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH v4 02/11] memcg: document cgroup dirty memory interfaces
    Hi Greg,

    On Fri, Oct 29, 2010 at 03:09:05PM +0800, Greg Thelen wrote:

    > Document cgroup dirty memory interfaces and statistics.
    >
    > Signed-off-by: Andrea Righi <arighi@develer.com>
    > Signed-off-by: Greg Thelen <gthelen@google.com>
    > ---

    > +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.

    It's more pertinent to say "will be throttled", as "perform write-out"
    is some implementation behavior that will change soon.

    > +- 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.

    The suffix feature is handy, thanks! It makes sense to also add this
    for the global interfaces, perhaps in a standalone patch.

    > +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.

    It's good to document the above "misbehavior". But why not throttling
    the dirtying cgroup B task? Is it simply not implemented or makes no
    sense to do so at all?

    Thanks,
    Fengguang


    \
     
     \ /
      Last update: 2010-10-29 13:07    [W:3.300 / U:0.000 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site