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Re: [Qemu-devel] [PATCH V12 4/5] util/mmap-alloc: support MAP_SYNC in qe
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PATCH V12 4/5] util/mmap-alloc: support MAP_SYNC in qemu_ram_mmap() |
Date: |
Wed, 6 Feb 2019 13:25:09 -0500 |
On Thu, Feb 07, 2019 at 01:27:19AM +0800, Zhang, Yi wrote:
> From: Zhang Yi <address@hidden>
>
> 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 <address@hidden>
> Signed-off-by: Zhang Yi <address@hidden>
> ---
> include/qemu/osdep.h | 7 +++++++
> util/mmap-alloc.c | 24 +++++++++++++++++++++++-
> 2 files changed, 30 insertions(+), 1 deletion(-)
>
> diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
> index 457d24e..9a94cc3 100644
> --- a/include/qemu/osdep.h
> +++ b/include/qemu/osdep.h
> @@ -115,6 +115,13 @@ extern int daemon(int, int);
> #include "sysemu/os-win32.h"
> #endif
>
> +#ifdef CONFIG_LINUX
> +#include <linux/mman.h>
> +#else /* !CONFIG_LINUX */
> +#define MAP_SYNC 0x0
> +#define MAP_SHARED_VALIDATE 0x0
> +#endif /* CONFIG_LINUX */
> +
> #ifdef CONFIG_POSIX
> #include "sysemu/os-posix.h"
> #endif
It's only used in one place. Maybe put this code in mmap-alloc.c ?
> diff --git a/util/mmap-alloc.c b/util/mmap-alloc.c
> index 97bbeed..e4e55fc 100644
> --- a/util/mmap-alloc.c
> +++ b/util/mmap-alloc.c
> @@ -15,6 +15,7 @@
> #include "qemu/host-utils.h"
>
> #define HUGETLBFS_MAGIC 0x958458f6
> +#define MAP_SYNC_FLAGS (MAP_SYNC | MAP_SHARED_VALIDATE)
>
Pls don't do this, just put it in a local variable within qemu_ram_mmap.
> #ifdef CONFIG_LINUX
> #include <sys/vfs.h>
> @@ -101,6 +102,7 @@ void *qemu_ram_mmap(int fd,
> #else
> void *ptr = mmap(0, total, PROT_NONE, MAP_ANONYMOUS | MAP_PRIVATE, -1,
> 0);
> #endif
> + int mmap_flags;
> size_t offset;
> void *ptr1;
>
> @@ -111,13 +113,33 @@ void *qemu_ram_mmap(int fd,
> assert(is_power_of_2(align));
> /* Always align to host page size */
> assert(align >= getpagesize());
> + mmap_flags = shared ? MAP_SHARED : MAP_PRIVATE;
> + if (shared && is_pmem) {
> + mmap_flags |= MAP_SYNC_FLAGS;
> + }
>
> offset = QEMU_ALIGN_UP((uintptr_t)ptr, align) - (uintptr_t)ptr;
> ptr1 = mmap(ptr + offset, size, PROT_READ | PROT_WRITE,
> MAP_FIXED |
> (fd == -1 ? MAP_ANONYMOUS : 0) |
> - (shared ? MAP_SHARED : MAP_PRIVATE),
> + mmap_flags,
> fd, 0);
> +
> +
> + if (ptr1 == MAP_FAILED &&
> + (mmap_flags & MAP_SYNC_FLAGS) == MAP_SYNC_FLAGS) {
> + if (errno == ENOTSUP) {
> + perror("failed to validate with mapping flags");
I don't think this warning message makes sense.
Are you trying to say:
Warning: requesting persistence across crashes
for file XYZ failed. Proceeding without persistence,
data might become corrupted in case of host crash.
?
> + }
> + /* if map failed with MAP_SHARED_VALIDATE | MAP_SYNC,
> + * we will remove these flags to handle compatibility.
> + */
> + ptr1 = mmap(ptr + offset, size, PROT_READ | PROT_WRITE,
> + MAP_FIXED |
> + (fd == -1 ? MAP_ANONYMOUS : 0) |
> + MAP_SHARED,
> + fd, 0);
> + }
> if (ptr1 == MAP_FAILED) {
> munmap(ptr, total);
> return MAP_FAILED;
> --
> 2.7.4
- [Qemu-devel] [PATCH V12 0/5] support MAP_SYNC for memory-backend-file, Zhang, Yi, 2019/02/06
- [Qemu-devel] [PATCH V12 3/5] linux-headers: add linux/mman.h., Zhang, Yi, 2019/02/06
- [Qemu-devel] [PATCH V12 4/5] util/mmap-alloc: support MAP_SYNC in qemu_ram_mmap(), Zhang, Yi, 2019/02/06
- Re: [Qemu-devel] [PATCH V12 4/5] util/mmap-alloc: support MAP_SYNC in qemu_ram_mmap(),
Michael S. Tsirkin <=
- [Qemu-devel] [PATCH V12 5/5] docs: Added MAP_SYNC documentation, Zhang, Yi, 2019/02/06
[Qemu-devel] [PATCH V12 1/5] util/mmap-alloc: Add a 'is_pmem' parameter to qemu_ram_mmap, Zhang, Yi, 2019/02/06
[Qemu-devel] [PATCH V12 2/5] scripts/update-linux-headers: add linux/mman.h, Zhang, Yi, 2019/02/06