* Theodore Tso <tytso@xxxxxxx> [2009-04-21 13:46:20]: > On Tue, Apr 21, 2009 at 10:53:17PM +0530, Balbir Singh wrote: > > Coming to the dirty page tracking issue, the issue that is being > > brought about is the same issue that we have shared page accounting. I > > am working on estimates for shared page accounting and it should be > > possible to extend it to dirty shared page accounting. Using the > > shared ratios for decisions might be a better strategy. > > It's the same issue, but again, consider the use case where the > readers and the writers are in different cgroups. This can happen > quite often in database workloads, where you might have many readers, > and a single process doing the database update. Or the case where you > have one process in one cgroup doing a tail -f of some log file, and > another process doing writing to the log file. > 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. > Using a shared ratio is certainly better than charging 100% of the > write to whichever unfortunate process happened to first read the > page, but it will still not be terribly accurate. A lot really > depends on how you expect these cgroup limits will be used, and what > the requirements actually will be with respect to accuracy. If the > requirements for accuracy are different for RSS tracking and dirty > page tracking --- which could easily be the case, since memory is > usually much cheaper than I/O bandwidth, and there is generally far > more clean memory pages than there are dirty memory pages, so a small > numberical error in dirty page accounting translates to a much larger > percentage error than read-only RSS page accounting --- it may make > sense to use different mechanisms for tracking the two, given the > different requirements and differring overhead implications. > > Anyway, something for you to think about. Yep, but I would recommend using the controller we have, if the overheads span out to be too large for IO, we think about alternatives. -- Balbir _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers
