Il 16/05/2013 15:41, Gleb Natapov ha scritto:
> On Thu, May 16, 2013 at 03:14:35PM +0200, Paolo Bonzini wrote:
>> Il 16/05/2013 14:43, Gleb Natapov ha scritto:
>>>>> +restart:
>>>>> + list_for_each_entry_safe(sp, node, &kvm->arch.active_mmu_pages, link) {
>>>>> + if (!is_obsolete_sp(kvm, sp))
>>>>> + continue;
>>> What if we save kvm->arch.active_mmu_pages on the stack and init
>>> kvm->arch.active_mmu_pages to be empty at the entrance to
>>> zap_invalid_pages(). This loop will iterate over saved list. This will
>>> allow us to drop the is_obsolete_sp() check and will save time since we
>>> will not be iterating over newly created sps.
>>>
>>
>> But when you add cond_resched_lock a thread may want to zap pages itself
>> (e.g. from prepare_zap_oldest_mmu_page) and it won't find them.
>>
> Yes, this will break mmu pages accounting. We can make
> prepare_zap_oldest_mmu_page() wait while zap_invalid_pages()
> frees needed amount of pages if one is in progress.
>
>> Here is another proposal... The idea is to avoid looking at new pages
>> more than necessary after a "goto restart".
>>
>> Basically, you alternate between two phases:
>>
>> - look for pages to be zapped, group them together
>>
>> - zap the pages
>>
>> Something like:
>>
>> moved = 0;
>> restart:
>> zapping = true;
>> for each page in active_mmu_pages [reverse and safe] {
>> if (!is_obsolete || invalid) {
>> /*
>> * Found a new page, stop zapping for now and
>> * try to segregate the invalid ones at one end
>> * of the list.
>> */
>> zapping = false;
>> continue;
>> }
>>
>> if (batch > 10 && ...) {
>> cond_resched_lock
>> batch = 0;
>> goto restart;
>> }
>>
>> if (!zapping) {
>> /*
>> * Segregate pages to one end of the list where
>> * new pages don't get in the way.
>> */
>> list_move_tail(page, active_mmu_pages)
>> batch++; /* or maybe not? */
>> moved++;
>> } else {
>> batch += prepare_zap_page
>> goto restart;
>> }
>> }
>>
>> /* Need another pass to look at segregated pages? */
>> if (moved) {
>> moved = 0;
>> goto restart;
>> }
> Not sure what are you trying to achieve with "moved" tricks. Just
> walking the list from the end and stopping on first valid sp should be
> enough since active_mmu_pages list is a FIFO right now.
Right, I missed that "sp->role.invalid = 1" will ensure anyway that
pages are visited at most twice.
Paolo
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