Re: [Xen-devel] Proposed new "memory capacity claim" hypercall/feature

[Keir Fraser <keir@xxxxxxx>]

On 02/11/2012 09:01, "Jan Beulich" <JBeulich@xxxxxxxx> wrote:

> Plus, if necessary, that loop could be broken up so that only the
> initial part of it gets run with the lock held (see c/s
> 22135:69e8bb164683 for why the unlock was moved past the
> loop). That would make for a shorter lock hold time, but for a
> higher allocation latency on large oder allocations (due to worse
> cache locality).

In fact I believe only the first page needs to have its count_info set to !=
PGC_state_free, while the lock is held. That is sufficient to defeat the
buddy merging in free_heap_pages(). Similarly, we could hoist most of the
first loop in free_heap_pages() outside the lock. There's a lot of scope for
optimisation here.

 -- Keir



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