Messages in this thread | | | Date | Wed, 17 Jun 2015 17:48:52 -0400 | From | Theodore Ts'o <> | Subject | Re: [PATCH 3/3] writeback, blkio: add documentation for cgroup writeback support |
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On Wed, Jun 17, 2015 at 02:52:37PM -0400, Tejun Heo wrote: > > Hmmm... so, overriding things *before* an bio is issued shouldn't be > too difficult and as long as this sort of operations aren't prevalent > we might be able to get away with just charging them against root. > Especially if it's to avoid getting blocked on the journal which we > already consider a shared overhead which is charged to root. If this > becomes large enough to require exacting charges, it'll be more > complex but still way better than trying to raise priority on a bio > which is already issued, which is likely to be excruciatingly painful > if possible at all.
Yeah, just charging the overhead to root seems good enough.
I could imagine charging it to whatever cgroup the jbd/jbd2 thread belongs to, which in turn would be the cgroup of the process that mounted the file system. The only problem with that is that if a low-priority process is allowed to mount a file system, and it gets traversed by a high priority process, the high priority process will get impacted. So maybe it's better to just say that it always get charged to the root cgroup.
- Ted
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