Messages in this thread | | | Date | Tue, 02 Nov 2004 08:55:15 -0800 | From | "Martin J. Bligh" <> | Subject | Re: [PATCH] Use MPOL_INTERLEAVE for tmpfs files |
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--Andi Kleen <ak@suse.de> wrote (on Tuesday, November 02, 2004 16:55:07 +0100):
> On Tue, Nov 02, 2004 at 07:46:59AM -0800, Martin J. Bligh wrote: >> > This patch causes memory allocation for tmpfs files to be distributed >> > evenly across NUMA machines. In most circumstances today, tmpfs files >> > will be allocated on the same node as the task writing to the file. >> > In many cases, particularly when large files are created, or a large >> > number of files are created by a single task, this leads to a severe >> > imbalance in free memory amongst nodes. This patch corrects that >> > situation. >> >> Yeah, but it also ruins your locality of reference (in a NUMA sense). >> Not convinced that's a good idea. You're guaranteeing universally consistent >> worse-case performance for everyone. And you're only looking at a situation >> where there's one allocator on the system, and that's imbalanced. >> >> You WANT your data to be local. That's the whole idea. > > I think it depends on how you use tmpfs. When you use it for read/write > it's a good idea because you likely don't care about a bit of additional > latency and it's better to not fill up your local nodes with temporary > files. > > If you use it with mmap then you likely want local policy. > > But that's a big ugly to distingush, that is why I suggested the sysctl.
As long as it defaults to off, I guess I don't really care. Though I'm still wholly unconvinced it makes much sense. I think we're just papering over the underlying problem - that we don't do good balancing between nodes under mem pressure.
M.
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