From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:37471) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1a3id8-000427-Hb for qemu-devel@nongnu.org; Tue, 01 Dec 2015 05:57:55 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1a3id5-0006hD-9V for qemu-devel@nongnu.org; Tue, 01 Dec 2015 05:57:54 -0500 Received: from mx1.redhat.com ([209.132.183.28]:37152) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1a3id5-0006h6-3i for qemu-devel@nongnu.org; Tue, 01 Dec 2015 05:57:51 -0500 Date: Tue, 1 Dec 2015 12:57:47 +0200 From: "Michael S. Tsirkin" Message-ID: <20151201125659-mutt-send-email-mst@redhat.com> References: <20151130105044.12269.21261.stgit@bahia.huguette.org> <20151130150353-mutt-send-email-mst@redhat.com> <20151130144631.4736280b@bahia.local> <20151130185328-mutt-send-email-mst@redhat.com> <878u5eqw2w.fsf@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <878u5eqw2w.fsf@linux.vnet.ibm.com> Subject: Re: [Qemu-devel] [PATCH] mmap-alloc: use same backend for all mappings List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Aneesh Kumar K.V" Cc: Paolo Bonzini , qemu-devel@nongnu.org, Greg Kurz On Tue, Dec 01, 2015 at 04:23:11PM +0530, Aneesh Kumar K.V wrote: > "Michael S. Tsirkin" writes: > > > On Mon, Nov 30, 2015 at 02:46:31PM +0100, Greg Kurz wrote: > >> On Mon, 30 Nov 2015 15:06:33 +0200 > >> "Michael S. Tsirkin" wrote: > >> > > > .... > >> > >> On ppc64, the address space is divided in 256MB-sized segments where all pages > >> have the same size. This is a hw limitation IIUC. I don't know if it can be > >> fixed and I'll let Ben comment on it. > > > > But it's anonymous memory with PROT_NONE. There should be no pages there: > > just a chunk of virtual memory reserved. > > > > ppc64 use page size (called as base page size) to find the hash slot in > which we find the virtual address to real address translation. All the > pages in a segment should have same base page size. Hugetlb pages have a > base page size of 16M whereas a regular linux page have 64K. mmap will > fail to map a hugetlb mapping in a segment that already have regular > pages mapped. > > -aneesh I see this in kernel: } else if (flags & MAP_HUGETLB) { struct user_struct *user = NULL; struct hstate *hs; hs = hstate_sizelog((flags >> MAP_HUGE_SHIFT) & SHM_HUGE_MASK); if (!hs) return -EINVAL; len = ALIGN(len, huge_page_size(hs)); /* * VM_NORESERVE is used because the reservations will be * taken when vm_ops->mmap() is called * A dummy user value is used because we are not locking * memory so no accounting is necessary */ file = hugetlb_file_setup(HUGETLB_ANON_FILE, len, VM_NORESERVE, &user, HUGETLB_ANONHUGE_INODE, (flags >> MAP_HUGE_SHIFT) & MAP_HUGE_MASK); if (IS_ERR(file)) return PTR_ERR(file); } So maybe it's a question of passing in MAP_HUGETLB and the correct size mask. -- MST