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@xxxxxxxxxxx> > Signed-off-by: Greg Thelen <gthelen@xxxxxxxxxx> > --- > +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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>