* Theodore Tso <tytso@xxxxxxx> [2009-04-21 15:14:01]: > On Tue, Apr 21, 2009 at 11:44:29PM +0530, Balbir Singh wrote: > > > > That would be true in general, but only the process writing to the > > file will dirty it. So dirty already accounts for the read/write > > split. I'd assume that the cost is only for the dirty page, since we > > do IO only on write in this case, unless I am missing something very > > obvious. > > Maybe I'm missing something, but the (in development) patches I saw > seemed to use the existing infrastructure designed for RSS cost > tracking (which is also not yet in mainline, unless I'm mistaken --- > but I didn't see page_get_page_cgroup() in the mainline tree yet). > > Right? So if process A in cgroup A reads touches the file first by > reading from it, then the pages read by process A will be assigned as > being "owned" by cgroup A. Then when the patch described at > > http://lkml.org/lkml/2008/9/9/245 That is correct, but on reclaim (hitting the limit) a page that is frequently used by B and not A, can get reclaimed from A and move to B if B is heavily using it. > > ... tries to charge a write done by process B in cgroup B, the code > will call page_get_page_cgroup(), see that it is "owned" by cgroup A, > and charge the dirty page to cgroup A. If process A and all of the > other processes in cgroup A only access this file read-only, and > process B is updating this file very heavily --- and it is a large > file --- then cgroup B will get a completely free pass as far as > dirtying pages to this file, since it will be all charged 100% to > cgroup A, incorrectly. > > So what am I missing? You are right. As long as A is not exceeding its limit, B will get a free pass at the page. The page will be inactive on A's LRU and active on the global LRU though from the memory controller perspective. We'll need to find a way to fix this, if this is a very common scenario for the IO controller. -- Balbir _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers
