From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([209.51.188.92]:56050) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gofc1-0004d6-46 for qemu-devel@nongnu.org; Tue, 29 Jan 2019 21:28:26 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gofbz-0007no-NG for qemu-devel@nongnu.org; Tue, 29 Jan 2019 21:28:24 -0500 Received: from mx1.redhat.com ([209.132.183.28]:56786) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1gofbz-0007nc-BF for qemu-devel@nongnu.org; Tue, 29 Jan 2019 21:28:23 -0500 Date: Tue, 29 Jan 2019 21:28:17 -0500 From: "Michael S. Tsirkin" Message-ID: <20190129212747-mutt-send-email-mst@kernel.org> References: <20190129083952-mutt-send-email-mst@kernel.org> <20190130103646.GA53874@tiger-server> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190130103646.GA53874@tiger-server> Subject: Re: [Qemu-devel] [PATCH v11 2/3] util/mmap-alloc: support MAP_SYNC in qemu_ram_mmap() List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: xiaoguangrong.eric@gmail.com, stefanha@redhat.com, pbonzini@redhat.com, pagupta@redhat.com, yu.c.zhang@linux.intel.com, richardw.yang@linux.intel.com, ehabkost@redhat.com, qemu-devel@nongnu.org, imammedo@redhat.com, dan.j.williams@intel.com On Wed, Jan 30, 2019 at 06:36:46PM +0800, Yi Zhang wrote: > On 2019-01-29 at 08:50:46 -0500, Michael S. Tsirkin wrote: > > On Tue, Jan 29, 2019 at 10:49:09PM +0800, Zhang, Yi wrote: > > > From: Zhang Yi > > > > > > 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). > > > > > > Current, We have below different possible use cases: > > > > > > 1. pmem=on is set, shared=on is set, MAP_SYNC supported: > > > a: backend is a dax supporting file. > > > - MAP_SYNC will active. > > > b: backend is not a dax supporting file. > > > - mmap will trigger a warning. then MAP_SYNC flag will be ignored > > > > > > 2. The rest of cases: > > > - we will never pass the MAP_SYNC to mmap2 > > > > > > Signed-off-by: Haozhong Zhang > > > Signed-off-by: Zhang Yi > > > --- > > > include/qemu/osdep.h | 21 +++++++++++++++++++++ > > > util/mmap-alloc.c | 28 +++++++++++++++++++++++++++- > > > 2 files changed, 48 insertions(+), 1 deletion(-) > > > > > > diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h > > > index 457d24e..96209bb 100644 > > > --- a/include/qemu/osdep.h > > > +++ b/include/qemu/osdep.h > > > @@ -419,6 +419,27 @@ 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 0x80000 > > > +#endif > > > + > > > +#ifndef MAP_SHARED_VALIDATE > > > +#define MAP_SHARED_VALIDATE 0x03 > > > +#endif > > > + > > > > I commented on this part in v7. That's a wrong way to handle > > compatibility. > MAP_SYNC and MAP_SHARED_VALIDATE have not defined at pre 4.15 kernel. > to handle the compatibility we should defined it, Right?, That is Why I > changed the value to run time handle the compatibility. > > in previous version, you comments that we shouldn't direct define that > in our own headers to avoid duplicated code. > > So we add #include Right? > > Then shouldn't consider build qemu on pre 4.15 kernel header? won't > failed? > > #ifndef MAP_SYNC > #define MAP_SYNC 0x80000 > #endif > > #ifndef MAP_SHARED_VALIDATE > #define MAP_SHARED_VALIDATE 0x03 > #endif > > forgive my poor understanding, I'm getting more confused. Look at how we handle other such defines such as e.g. kvm ioctl values. > > > > > We had this discussion several times in the past. commit log doesn't > > mention any reasons to ignore this. All for setting a single bit in a > > single system call. This is getting discouraging. > > > > > > > +#else /* !CONFIG_LINUX */ > > > +#define MAP_SYNC 0x0 > > > +#define MAP_SHARED_VALIDATE 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 97bbeed..2c86ad2 100644 > > > --- a/util/mmap-alloc.c > > > +++ b/util/mmap-alloc.c > > > @@ -101,6 +101,7 @@ void *qemu_ram_mmap(int fd, > > > #else > > > void *ptr = mmap(0, total, PROT_NONE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0); > > > #endif > > > + int mmap_xflags = 0; > > > > That's not a good variable name. It's extra for you since > > you are writing the patch but it makes no sense > > in the context of the function. Just mmap_flags > > will do - and I would put all flags there, not just > > the "extra" that this patch is adding. > > > > > > > size_t offset; > > > void *ptr1; > > > > > > @@ -111,13 +112,38 @@ void *qemu_ram_mmap(int fd, > > > assert(is_power_of_2(align)); > > > /* Always align to host page size */ > > > assert(align >= getpagesize()); > > > + if (shared && is_pmem) { > > > + mmap_xflags = MAP_SYNC | MAP_SHARED_VALIDATE; > > > + } > > > > > > offset = QEMU_ALIGN_UP((uintptr_t)ptr, align) - (uintptr_t)ptr; > > > +retry_mmap: > > > 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 map failed with MAP_SHARED_VALIDATE | MAP_SYNC, > > > + * we try with MAP_SHARED_VALIDATE without MAP_SYNC > > > + */ > > > + if (ptr1 == MAP_FAILED && > > > + mmap_xflags == (MAP_SYNC | MAP_SHARED_VALIDATE)) { > > > + if (errno == ENOTSUP) { > > > + perror("failed to validate with mapping flags"); > > > + } > > > + mmap_xflags = MAP_SHARED_VALIDATE; > > > + goto retry_mmap; > > > > Have you read > > https://homepages.cwi.nl/~storm/teaching/reader/Dijkstra68.pdf > > > > Please just call the function twice. You don't need goto > > to repeat a single line. > > > > > > > + } > > > + /* MAP_SHARED_VALIDATE flag is available since Linux 4.15 > > > + * Test only with MAP_SHARED_VALIDATE flag for compatibility. > > > + * Then ignore the MAP_SHARED_VALIDATE flag and retry again > > > + */ > > > + if (mmap_xflags == MAP_SHARED_VALIDATE && > > > + ptr1 == MAP_FAILED) { > > > + mmap_xflags &= ~MAP_SHARED_VALIDATE; > > > + goto retry_mmap; > > > + } > > > if (ptr1 == MAP_FAILED) { > > > munmap(ptr, total); > > > return MAP_FAILED; > > > -- > > > 2.7.4