Andrea Righi wrote: > On 2008-11-03 08:01, Gui Jianfeng wrote: >> Hi Andrea, >> >> I'v tested io-throttle(v11), it seems io-throttle doesn't work well >> when a process writes(delay-write) a small file(<50M may be). it can't >> throttle the request process accurately. >> I guess the following reason causes this problem. >> The write-request process terminates too early to see all accounting >> calculated in pdflush. So io-throttle can't throttle >> enough time for that process. Am i right? > > Hi Gui, > > sorry for my late first of all. You're right in part. The fact is that > with asynchronous IO (no O_DIRECT more exactly) the accounting is > performed when the blocks are submitted to the IO subsystem (submit_bio) > and the throttling is performed post-facto when the same process or the > other processes in the same cgroup write additional pages mapped to the > limited device (throttling is performed in > balance_dirty_pages_ratelimited_nr). > > Anyway, if the process did a single small write in memory the operation > is not accounted until pdflush writes the data back to the block device. > When pdflush (or the process itself) performs the writeback the > operation is accounted and next reads/writes that come from the same > cgroup can now be throttled according to the defined limits. > > So, the accounting is not lost, this information is only used later to > throttle the next operations that will cause IO requests. IO spikes in > this way are not prevented. With an early version of io-throttle I did > both throttling and accounting in balance_dirty_pages_ratelimited_nr > (when pages are written to memory), this can prevent IO spikes, but only > if dirty_ratio is set to small values. Hi, Andrea, Thanks for your detailed explanation, I'v got your point. I think it makes more sense if throttling can be fair among other tasks. ;-) > > Hope this clarify, > -Andrea > > > -- Regards Gui Jianfeng _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers
