From mboxrd@z Thu Jan 1 00:00:00 1970 From: Izik Eidus Subject: Re: [PATCH 3/4] Swapping Date: Sun, 14 Oct 2007 01:26:39 +0200 Message-ID: <4711542F.2060306@qumranet.com> References: <47102919.6070802@qumranet.com> <471124D4.3090901@codemonkey.ws> <471126D9.4030204@qumranet.com> <47112D66.4020500@qumranet.com> <47115207.3090909@codemonkey.ws> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org To: Anthony Liguori Return-path: In-Reply-To: <47115207.3090909-rdkfGonbjUSkNkDKm+mE6A@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Errors-To: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: kvm.vger.kernel.org Anthony Liguori wrote: > Izik Eidus wrote: >> Izik Eidus wrote: >>> Anthony Liguori wrote: >>>> Izik Eidus wrote: >>>>> >>>>> @@ -1058,8 +1038,27 @@ struct page *gfn_to_page(struct kvm *kvm, >>>>> gfn_t gfn) >>>>> >>>>> gfn = unalias_gfn(kvm, gfn); >>>>> slot = __gfn_to_memslot(kvm, gfn); >>>>> - if (!slot) >>>>> + if (!slot) { >>>>> + get_page(bad_page); >>>>> return bad_page; >>>>> + } >>>>> + if (slot->user_alloc) { >>>>> + struct page *page[1]; >>>>> + int npages; >>>>> + >>>>> + down_read(¤t->mm->mmap_sem); >>>>> + npages = get_user_pages(current, current->mm, >>>>> + slot->userspace_addr >>>>> + + (gfn - slot->base_gfn) * PAGE_SIZE, 1, >>>>> + 1, 0, page, NULL); >>>>> + up_read(¤t->mm->mmap_sem); >>>>> + if (npages != 1) { >>>>> + get_page(bad_page); >>>>> + return bad_page; >>>>> + } >>>>> + return page[0]; >>>>> >>>> >>>> Wouldn't it be necessary to assign page[0] to slot->phys_mem[gfn - >>>> slot->base_gfn]? >>> >> sorry, it seems like i missunderstand you in the answer i gave you. >> it wouldnt be necessary to assign page[0] to slot->phys_mem[gfn - >> slot->base_gfn], beacuse phys_mem wont have any memory allocate by >> this time. >> >> with this patch, we are not holding anymore (when using userspace >> allocation) array of all the memory at phys_mem. >> beacuse now that the pages are swappable, the physical address >> pointed by the virtual address all the time change (for example when >> swapping happn) >> so no one promise us that slot->phys_mem[gfn - slot->base_gfn] will >> really point to page holding the gfn page. >> >> so what we did, is throw away the phys_mem array (also nice beacuse >> it waste less ram), and at runtime we are getting the pages by using >> the virtual address >> beacuse the reference of the page get increased, it promised us that >> untill we release it point to the gfn (release it by doing put_page) >> >> hope i was more clear this time :) > > Yes, that makes sense! > > I wonder if there's a more elegant way dealing with older userspaces. > For instance, is there any reason why we can allocate a userspace > memory region on behalf of userspace. That way swap would even work > with older userspaces. if we can do that, yes swap will work on older userspace. > Regards, > > Anthony Liguori > > ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/