Re: [PATCH] shrinker support for the mmu cache

[Anthony Liguori <anthony@codemonkey.ws>]

Izik Eidus wrote:
> this patch simply register the mmu cache with the shrinker.

Please inline patches in the future as it makes it easier to review.  
The implementation looks good and I think it's a good idea.

One is that there is one shrinker for all VMs but you run through the 
list of VMs in order.  This means the first VM in the list is most 
frequently going to be shrunk down to KVM_MIN_ALLOC_MMU_PAGES.  This 
seems unfair and potentially dangerous.  The shrinker can be triggered 
potentially by the growth of the MMU cache on other VMs.

I think in the least, you should attempt to go through the VMs in a 
round-robin fashion to ensure that if you shrink one VM, the next time 
you'll shrink a different VM.

The other thing I wonder about is whether DEFAULT_SEEKS is the best 
value to use.  On the one hand, a guest page fault is probably not as 
expensive as reclaiming something from disk.  On the other hand, NPT 
guests are likely to be very sensitive to evicting things from the 
shadow page cache.  I would think it's pretty clear that in the NPT 
case, the MMU cache should have a higher seek cost than the default.

Regards,

Anthony Liguori

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