From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anthony Liguori Subject: Re: [PATCH 3/4] Swapping Date: Sat, 13 Oct 2007 18:35:25 -0500 Message-ID: <4711563D.8020000@codemonkey.ws> References: <47102919.6070802@qumranet.com> <471124D4.3090901@codemonkey.ws> <471126D9.4030204@qumranet.com> <47112D66.4020500@qumranet.com> <47115207.3090909@codemonkey.ws> <4711542F.2060306@qumranet.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org To: Izik Eidus Return-path: In-Reply-To: <4711542F.2060306-atKUWr5tajBWk0Htik3J/w@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 Izik Eidus wrote: > 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. I think it's just a matter of calling do_mmap() with the appropriate parameters. It looks likes there's some drivers call do_mmap() directly. Regards, Anthony Liguori >> 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/