From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([209.51.188.92]:49341) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gjEnH-00052w-PN for qemu-devel@nongnu.org; Mon, 14 Jan 2019 21:49:36 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gjEnG-0007Eu-Tv for qemu-devel@nongnu.org; Mon, 14 Jan 2019 21:49:35 -0500 Received: from mga03.intel.com ([134.134.136.65]:24863) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1gjEnG-0007EQ-Lw for qemu-devel@nongnu.org; Mon, 14 Jan 2019 21:49:34 -0500 Date: Tue, 15 Jan 2019 10:49:45 +0800 From: Yi Zhang Message-ID: <20190115024944.GB67749@tiger-server> References: <0b17cd9e914372c4790296b2cc21d6dd6e6d5466.1546399191.git.yi.z.zhang@linux.intel.com> <20190114190702.GE28115@habkost.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190114190702.GE28115@habkost.net> Subject: Re: [Qemu-devel] [PATCH V8 3/5] util/mmap-alloc: support MAP_SYNC in qemu_ram_mmap() List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Eduardo Habkost Cc: xiaoguangrong.eric@gmail.com, stefanha@redhat.com, pbonzini@redhat.com, pagupta@redhat.com, yu.c.zhang@linux.intel.com, mst@redhat.com, imammedo@redhat.com, dan.j.williams@intel.com, qemu-devel@nongnu.org On 2019-01-14 at 17:07:02 -0200, Eduardo Habkost wrote: > On Wed, Jan 02, 2019 at 01:26:15PM +0800, Zhang Yi wrote: > > When a file supporting DAX is used as vNVDIMM backend, mmap it with > > MAP_SYNC flag in addition which can ensure file system metadata > > synced in each guest writes to the backend file, without other QEMU > > actions (e.g., periodic fsync() by QEMU). > > > > Signed-off-by: Haozhong Zhang > > Signed-off-by: Zhang Yi > > --- > > include/qemu/osdep.h | 16 ++++++++++++++++ > > util/mmap-alloc.c | 12 +++++++++++- > > 2 files changed, 27 insertions(+), 1 deletion(-) > > > > diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h > > index 3bf48bc..bb1eba1 100644 > > --- a/include/qemu/osdep.h > > +++ b/include/qemu/osdep.h > > @@ -410,6 +410,22 @@ void qemu_anon_ram_free(void *ptr, size_t size); > > # define QEMU_VMALLOC_ALIGN getpagesize() > > #endif > > > > +/* > > + * MAP_SHARED_VALIDATE and MAP_SYNC are introduced in Linux kernel > > + * 4.15, so they may not be defined when compiling on older kernels. > > + */ > > +#ifdef CONFIG_LINUX > > + > > +#include > > + > > +#ifndef MAP_SYNC > > +#define MAP_SYNC 0x0 > > +#endif > > + > > +#else /* !CONFIG_LINUX */ > > +#define MAP_SYNC 0x0 > > +#endif /* CONFIG_LINUX */ > > + > > #ifdef CONFIG_POSIX > > struct qemu_signalfd_siginfo { > > uint32_t ssi_signo; /* Signal number */ > > diff --git a/util/mmap-alloc.c b/util/mmap-alloc.c > > index 8f0a740..a9d5e56 100644 > > --- a/util/mmap-alloc.c > > +++ b/util/mmap-alloc.c > > @@ -99,6 +99,8 @@ void *qemu_ram_mmap(int fd, size_t size, size_t align, uint32_t flags) > > void *ptr = mmap(0, total, PROT_NONE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0); > > #endif > > bool shared = flags & RAM_SHARED; > > + bool is_pmem = flags & RAM_PMEM; > > + int mmap_xflags = 0; > > size_t offset; > > void *ptr1; > > > > @@ -109,13 +111,21 @@ void *qemu_ram_mmap(int fd, size_t size, size_t align, uint32_t flags) > > assert(is_power_of_2(align)); > > /* Always align to host page size */ > > assert(align >= getpagesize()); > > + if (shared && is_pmem) { > > + mmap_xflags |= MAP_SYNC; > > + } > > > > offset = QEMU_ALIGN_UP((uintptr_t)ptr, align) - (uintptr_t)ptr; > > + retry_mmap_fd: > > ptr1 = mmap(ptr + offset, size, PROT_READ | PROT_WRITE, > > MAP_FIXED | > > (fd == -1 ? MAP_ANONYMOUS : 0) | > > - (shared ? MAP_SHARED : MAP_PRIVATE), > > + (shared ? MAP_SHARED : MAP_PRIVATE) | mmap_xflags, > > fd, 0); > > + if ((ptr1 == MAP_FAILED) && (mmap_xflags & MAP_SYNC)) { > > + mmap_xflags &= ~MAP_SYNC; > > + goto retry_mmap_fd; > > Do we have use cases where using pmem=on without MAP_SYNC isn't > going to cause problems? If not, shouldn't we at least print a Yes, we have a case that direct use dax device but not a files on dax aware file system, we prefer to don't set the MAP_SYNC if user haven't much knowledge about that. it may took some potencial performance issues with MAP_SYNC. > warning here? Otherwise, won't we still need an option for cases > that require MAP_SYNC to be working? > > > + } > > -- > Eduardo