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 <haozhong.zh...@intel.com>
> Signed-off-by: Zhang Yi <yi.z.zh...@linux.intel.com>
> ---
> 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 <asm-generic/mman.h>
> +
> +#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
warning here? Otherwise, won't we still need an option for cases
that require MAP_SYNC to be working?
> + }
--
Eduardo
