linux-kernel - Re: [PATCH 1/3] kvm: memslots: track id_to_index changes during the insertion sort

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Message-ID: <546611E5.2090209@redhat.com>
Date:	Fri, 14 Nov 2014 15:29:57 +0100
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	kvm@...r.kernel.org
Subject: Re: [PATCH 1/3] kvm: memslots: track id_to_index changes during the
 insertion sort



On 14/11/2014 14:35, Radim Krčmář wrote:
> We are replacing in a sorted array, so the the direction of our
> traversal doesn't change, (and we could lose one tab level here,)
> 
> 	if (new->npages < mslots[i].npages) {
> 		while (i < (KVM_MEM_SLOTS_NUM - 1) &&
> 		       new->npages < mslots[i + 1].npages) {
> 			mslots[i] = mslots[i + 1];
> 			slots->id_to_index[mslots[i].id] = i;
> 			i++;
> 		}
> 	else if (new->npages > mslots[i].npages)
> 		while (i > 0 &&
> 		       new->npages > mslots[i - 1].npages) {
> 			mslots[i] = mslots[i - 1];
> 			slots->id_to_index[mslots[i].id] = i;
> 			i--;
> 		}
> 
> (I guess you don't want me to abstract these two loops further :)

Right.  You do not need the "else if" as long as you keep the outer "if
(new->npages != mslots[i].npages)".

> (We'll have to change it into an interval tree, or something, if the
>  number of slots rises anyway.)

I don't think that's needed, actually.  gfn_to_page and gfn_to_memslot
are very rarely in the profiles with EPT.

Paolo

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