From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gleb Natapov Subject: Re: [PATCH unit-tests] Add async page fault test Date: Wed, 9 May 2012 11:59:17 +0300 Message-ID: <20120509085917.GR15960@redhat.com> References: <20120508112446.GB8988@redhat.com> <4FAA2AD7.7050109@redhat.com> <20120509084119.GP15960@redhat.com> <4FAA3059.2040105@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: kvm@vger.kernel.org, mtosatti@redhat.com To: Avi Kivity Return-path: Received: from mx1.redhat.com ([209.132.183.28]:49750 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757901Ab2EII7T (ORCPT ); Wed, 9 May 2012 04:59:19 -0400 Received: from int-mx01.intmail.prod.int.phx2.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id q498xJZW001965 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK) for ; Wed, 9 May 2012 04:59:19 -0400 Content-Disposition: inline In-Reply-To: <4FAA3059.2040105@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On Wed, May 09, 2012 at 11:52:41AM +0300, Avi Kivity wrote: > On 05/09/2012 11:41 AM, Gleb Natapov wrote: > > > > > > > void vfree(void *mem) > > > > { > > > > unsigned long size = ((unsigned long *)mem)[-1]; > > > > diff --git a/lib/x86/vm.h b/lib/x86/vm.h > > > > index 71ab4a8..ff4842f 100644 > > > > --- a/lib/x86/vm.h > > > > +++ b/lib/x86/vm.h > > > > @@ -22,6 +22,7 @@ void vfree(void *mem); > > > > void *vmap(unsigned long long phys, unsigned long size); > > > > void *alloc_vpage(void); > > > > void *alloc_vpages(ulong nr); > > > > +unsigned long virt_to_phys_cr3(void *mem); > > > > > > uint64_t. > > virt_to_phys() also unsigned long. And get_pte() that virt_to_phys_cr3() > > uses also. I guess the code is not ready for more then 2^32 memory in > > 32bit VM. > > It's certainly not enterprise quality yet. But let's not add more problems. > Okay. > > > Alterative ways of doing this: > > > - file-backed memory using FUSE to control paging > > Not sure how that can be done. > > > > > - add madvise(MADV_DONTNEED) support to testdev, and have the guest > > > trigger page-in itself. > > MADV_DONTNEED will drop page, not swap it out. > > Right, but it will be have to be reloaded from disk (it has to be > file-backed for this to work). If it's dirty, sync it first. > Hmm, yes if it is file backed it may work. Setting up qemu to use file backed memory is one more complication while running the test though. I haven't checked by I am not sure that MADV_DONTNEED will drop page immediately though. It probably puts it on some list to be freed later. Hmm actually looking at the comments it seems like this is what happens: /* * Application no longer needs these pages. If the pages are dirty, * it's OK to just throw them away. The app will be more careful about * data it wants to keep. Be sure to free swap resources too. The * zap_page_range call sets things up for shrink_active_list to actually * free * these pages later if no one else has touched them in the meantime, * although we could add these pages to a global reuse list for * shrink_active_list to pick up before reclaiming other pages. */ -- Gleb.