Messages in this thread | | | Date | Thu, 18 Sep 2008 10:10:28 +0900 | From | Kazuo Ito <> | Subject | Re: [PATCH] dm-snapshot: poor copy-on-write performance due to I/O reordering |
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Hi,
Bodo Eggert wrote: > Kazuo Ito <ito.kazuo@oss.ntt.co.jp> wrote: > >> Write throughput to LVM snapshot origin volume is an order >> of magnitude slower than those to LV without snapshots or >> snapshot target volumes, especially in the case of sequential >> writes with O_SYNC on. >> >> The following patch originally written by Kevin Jamieson and >> Jan Blunck and slightly modified for the current RCs by myself >> tries to improve the performance by modifying the behaviour >> of kcopyd, so that it pushes back an I/O job to the head of >> the job queue instead of the tail as process_jobs() currently >> does when it has to wait for free pages. This way, write >> requests aren't shuffled to cause extra seeks. > > Did you check for starvation problems, too?
I ran sadc along with the tests and figures like %memused, kbbuffers and kbcached didn't change much before and after the patch. And since the buffered I/O results didn't deteriorate at least in the cases of 10 and 100 megabyte sequential writes, I assumed there should be plentiful of memory for the kernel to use at least in these cases.
Anyway I can send you more detailed info upon your request.
Regards,
Kazuo Ito, NTT Open Source Software Center Phone: +81-3-5860-5125 / FAX: +81-3-5463-5690 / E-mail: ito.kazuo@oss.ntt.co.jp
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