From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43879) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1cdL57-0005bM-0J for qemu-devel@nongnu.org; Mon, 13 Feb 2017 13:10:34 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1cdL55-0002Z2-IE for qemu-devel@nongnu.org; Mon, 13 Feb 2017 13:10:32 -0500 Received: from mx1.redhat.com ([209.132.183.28]:58096) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1cdL55-0002Yx-CA for qemu-devel@nongnu.org; Mon, 13 Feb 2017 13:10:31 -0500 Date: Mon, 13 Feb 2017 19:10:28 +0100 From: Andrea Arcangeli Message-ID: <20170213181028.GH25530@redhat.com> References: <20170206173306.20603-1-dgilbert@redhat.com> <20170206174529.GI2524@work-vm> <20170213171058.GA4246@aperevalov-ubuntu> <20170213175722.GG25530@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170213175722.GG25530@redhat.com> Subject: Re: [Qemu-devel] [PATCH v2 00/16] Postcopy: Hugepage support List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Alexey Perevalov Cc: "Dr. David Alan Gilbert" , qemu-devel@nongnu.org, quintela@redhat.com, Mike Kravetz On Mon, Feb 13, 2017 at 06:57:22PM +0100, Andrea Arcangeli wrote: > Hello, > > On Mon, Feb 13, 2017 at 08:11:06PM +0300, Alexey Perevalov wrote: > > Another one request. > > QEMU could use mem_path in hugefs with share key simultaneously > > (-object memory-backend-file,id=mem,size=${mem_size},mem-path=${mem_path},share=on) and vm > > in this case will start and will properly work (it will allocate memory > > with mmap), but in case of destination for postcopy live migration > > UFFDIO_COPY ioctl will fail for > > such region, in Arcangeli's git tree there is such prevent check > > (if (!vma_is_shmem(dst_vma) && dst_vma->vm_flags & VM_SHARED). > > Is it possible to handle such situation at qemu? > > It'd be nice to lift this hugetlbfs !VM_SHARED restriction I agree, I > already asked Mike (CC'ed) why is there, because I'm afraid it's a Cc'ed not existent email, mail client autocompletion error, corrected the CC. > leftover from the anon version where VM_SHARED means a very different > thing but it was already lifted for shmem. share=on should already > work on top of tmpfs and also with THP on tmpfs enabled. > > For hugetlbfs and shmem it should be generally more complicated to > cope with private mappings than shared ones, shared is just the native > form of the pseudofs without having to deal with private COWs aliases > so it's hard to imagine something going wrong for VM_SHARED if the > MAP_PRIVATE mapping already works fine. If it turns out to be > superflous the check may be just turned into > "vma_is_anonymous(dst_vma) && dst_vma->vm_flags & VM_SHARED". > > Thanks, > Andrea