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Message-ID: <ba84ec1f-79f2-e15b-e225-7d2e2885a4c6@redhat.com> Date: Tue, 9 Apr 2019 09:05:16 +0200 From: David Hildenbrand <david@...hat.com> To: "Michael S. Tsirkin" <mst@...hat.com>, Alexander Duyck <alexander.duyck@...il.com> Cc: Nitesh Narayan Lal <nitesh@...hat.com>, kvm list <kvm@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, linux-mm <linux-mm@...ck.org>, Paolo Bonzini <pbonzini@...hat.com>, lcapitulino@...hat.com, pagupta@...hat.com, wei.w.wang@...el.com, Yang Zhang <yang.zhang.wz@...il.com>, Rik van Riel <riel@...riel.com>, dodgen@...gle.com, Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>, dhildenb@...hat.com, Andrea Arcangeli <aarcange@...hat.com> Subject: Re: Thoughts on simple scanner approach for free page hinting On 09.04.19 04:44, Michael S. Tsirkin wrote: > On Fri, Apr 05, 2019 at 05:09:45PM -0700, Alexander Duyck wrote: >> In addition we will need some way to identify which pages have been >> hinted on and which have not. The way I believe easiest to do this >> would be to overload the PageType value so that we could essentially >> have two values for "Buddy" pages. We would have our standard "Buddy" >> pages, and "Buddy" pages that also have the "Offline" value set in the >> PageType field. Tracking the Online vs Offline pages this way would >> actually allow us to do this with almost no overhead as the mapcount >> value is already being reset to clear the "Buddy" flag so adding a >> "Offline" flag to this clearing should come at no additional cost. > > It bothers me a bit that this doesn't scale to multiple hint types > if we ever need them. Would it be better to have two > free lists: hinted and non-hinted one? That would imply having to change all places trying to allocate memory to have a look at both lists? I think that could be factored out. I assume keeping track of the amount of pages would feel more naturally than having split counters for the existing lists. I think I'd actually prefer something like that, avoiding mixing page types and working with different types per list. -- Thanks, David / dhildenb
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