Messages in this thread | | | Date | Wed, 05 Aug 2009 11:15:07 -0400 | From | Rik van Riel <> | Subject | Re: [RFC] respect the referenced bit of KVM guest pages? |
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Avi Kivity wrote:
>> If so, we could unmap them when they get moved from the >> active to the inactive list, and soft fault them back in >> on access, emulating the referenced bit for EPT pages and >> making page replacement on them work like it should. > > It should be easy to implement via the mmu notifier callback: when the > mm calls clear_flush_young(), mark it as young, and unmap it from the > EPT pagetable.
You mean "mark it as old"?
>> Your approximation of pretending the page is accessed the >> first time and pretending it's not the second time sounds >> like it will just lead to less efficient FIFO replacement, >> not to anything even vaguely approximating LRU. > > Right, it's just a hack that gives EPT pages higher priority, like the > original patch suggested. Note that LRU for VMs is not a good > algorithm, since the VM will also reference the least recently used > page, leading to thrashing.
That is one of the reasons we use a very coarse two handed clock algorithm instead of true LRU.
LRU has more overhead and more artifacts :)
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