From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <48D2E65A.6020004@redhat.com> Date: Thu, 18 Sep 2008 16:38:02 -0700 From: Avi Kivity MIME-Version: 1.0 Subject: Re: Populating multiple ptes at fault time References: <48D142B2.3040607@goop.org> <48D17E75.80807@redhat.com> <48D1851B.70703@goop.org> <48D18919.9060808@redhat.com> <48D18C6B.5010407@goop.org> <48D2B970.7040903@redhat.com> <48D2D3B2.10503@goop.org> In-Reply-To: <48D2D3B2.10503@goop.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Jeremy Fitzhardinge Cc: Nick Piggin , Hugh Dickens , Linux Memory Management List , Linux Kernel Mailing List , Avi Kivity , Andrew Morton , Rik van Riel , Marcelo Tosatti List-ID: Jeremy Fitzhardinge wrote: > Avi Kivity wrote: > >>> Do you need to set the A bit synchronously? >>> >> Yes, of course (if no guest cooperation). >> > > Is the A bit architecturally guaranteed to be synchronously set? I believe so. The cpu won't cache tlb entries with the A bit clear (much like the shadow code), and will rmw the pte on first access. > Can > speculative accesses set it? Yes, but don't abuse this. >> If we add an async mode for guests that can cope, maybe this is >> workable. I guess this is what you're suggesting. >> >> > > Yes. At worst Linux would underestimate the process RSS a bit > (depending on how many unsynchronized ptes you leave lying around). I > Not the RSS (that's pte.present pages) but the working set (aka active list). > bet there's an appropriate pvop hook you could use to force > synchronization just before the kernel actually inspects the bits > (leaving lazy mode sounds good). > It would have to be a new lazy mode, not the existing one, I think. -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org