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Re: UVM patch for PR port-xen/45975
Chuck Silvers <chuq%chuq.com@localhost> wrote:
> - it would be better to remove the mappings before freeing the page
> on all platforms, not just xen. that's just a good practice.
> if you're concerned about a potential performance impact,
> you could process the pages in batches of 16 or so using a little
> array on the stack, which should handle most operations in one batch.
> I did a quick experiment just now and found that most calls
> to uvm_km_pgremove_intrsafe() are for 4 pages or less.
> (I wonder why those aren't using some higher-level cache?)
> about 10% of the calls were for 16 pages, and none were larger.
Yes. Also, one should be careful about potential race condition - that is,
TLB invalidations must happen *before* VA becomes available for use by other
processes. Otherwise, memory might be allocated with that VA range and used
while TLB caches have stale entries i.e. pointing to a wrong physical page.
> - the calls to pmap_update() should be moved along with the calls to
Due to deferred TLB invalidations (or flush), we want to call pmap_update()
at the point when all pmap_kremove() calls weere "collected".
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