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 <[email protected]>
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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