Messages in this thread | | | Date | Fri, 02 Nov 2007 00:00:10 +0100 | From | Eric Dumazet <> | Subject | Re: [patch 0/7] [RFC] SLUB: Improve allocpercpu to reduce per cpu access overhead |
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Christoph Lameter a écrit : > On Thu, 1 Nov 2007, David Miller wrote: > >> From: Christoph Lameter <clameter@sgi.com> >> Date: Thu, 1 Nov 2007 15:15:39 -0700 (PDT) >> >>> After boot is complete we allow the reduction of the size of the per cpu >>> areas . Lets say we only need 128k per cpu. Then the remaining pages will >>> be returned to the page allocator. >> You don't know how much you will need. I exhausted the limit on >> sparc64 very late in the boot process when the last few userland >> services were starting up. > > Well you would be able to specify how much will remain. If not it will > just keep the 2M reserve around. > >> And if I subsequently bring up 100,000 IP tunnels, it will exhaust the >> per-cpu allocation area. > > Each tunnel needs 4 bytes per cpu?
well, if we move last_rx to a percpu var, we need 8 bytes of percpu space per net_device :)
> >> You have to make it fully dynamic, there is no way around it. > > Na. Some reasonable upper limit needs to be set. If we set that to say > 32Megabytes and do the virtual mapping then we can just populate the first > 2M and only allocate the remainder if we need it. Then we need to rely on > Mel's defrag stuff though defrag memory if we need it.
If a 2MB page is not available, could we revert using 4KB pages ? (like vmalloc stuff), paying an extra runtime overhead of course.
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