Hello, David.
On Monday, February 3, 2020 3:31:20 PM -03 David Hildenbrand wrote:
> When shrinking a mmap we want to re-reserve the already populated area.
> When growing a memory region, we want to populate starting with a given
> fd_offset. Prepare by allowing to pass these parameters.
>
> Also, let's make sure we always process full pages, to avoid
> unmapping/remapping pages that are already in use when
> growing/shrinking. (existing callers seem to guarantee this, but that's
> not obvious)
>
> Cc: "Michael S. Tsirkin" <m...@redhat.com>
> Cc: Greg Kurz <gr...@kaod.org>
> Cc: Murilo Opsfelder Araujo <muri...@linux.ibm.com>
> Cc: Eduardo Habkost <ehabk...@redhat.com>
> Cc: "Dr. David Alan Gilbert" <dgilb...@redhat.com>
> Signed-off-by: David Hildenbrand <da...@redhat.com>
> ---
> util/mmap-alloc.c | 32 +++++++++++++++++++++-----------
> 1 file changed, 21 insertions(+), 11 deletions(-)
>
> diff --git a/util/mmap-alloc.c b/util/mmap-alloc.c
> index f043ccb0ab..63ad6893b7 100644
> --- a/util/mmap-alloc.c
> +++ b/util/mmap-alloc.c
> @@ -83,12 +83,12 @@ size_t qemu_mempath_getpagesize(const char *mem_path)
> }
>
> /*
> - * Reserve a new memory region of the requested size to be used for mapping
> - * from the given fd (if any).
> + * Reserve a new memory region of the requested size or re-reserve parts
> + * of an existing region to be used for mapping from the given fd (if any).
> */
> -static void *mmap_reserve(size_t size, int fd)
> +static void *mmap_reserve(void *ptr, size_t size, int fd)
> {
> - int flags = MAP_PRIVATE;
> + int flags = MAP_PRIVATE | (ptr ? MAP_FIXED : 0);
>
> #if defined(__powerpc64__) && defined(__linux__)
> /*
> @@ -111,19 +111,23 @@ static void *mmap_reserve(size_t size, int fd)
> flags |= MAP_ANONYMOUS;
> #endif
>
> - return mmap(0, size, PROT_NONE, flags, fd, 0);
> + return mmap(ptr, size, PROT_NONE, flags, fd, 0);
> }
>
> /*
> * Populate memory in a reserved region from the given fd (if any).
> */
> -static void *mmap_populate(void *ptr, size_t size, int fd, bool shared,
> - bool is_pmem)
> +static void *mmap_populate(void *ptr, size_t size, int fd, size_t
> fd_offset, + bool shared, bool is_pmem)
> {
> int map_sync_flags = 0;
> int flags = MAP_FIXED;
> void *new_ptr;
>
> + if (fd == -1) {
> + fd_offset = 0;
> + }
> +
> flags |= fd == -1 ? MAP_ANONYMOUS : 0;
> flags |= shared ? MAP_SHARED : MAP_PRIVATE;
> if (shared && is_pmem) {
> @@ -131,7 +135,7 @@ static void *mmap_populate(void *ptr, size_t size, int
> fd, bool shared, }
>
> new_ptr = mmap(ptr, size, PROT_READ | PROT_WRITE, flags |
> map_sync_flags, - fd, 0);
> + fd, fd_offset);
> if (new_ptr == MAP_FAILED && map_sync_flags) {
> if (errno == ENOTSUP) {
> char *proc_link = g_strdup_printf("/proc/self/fd/%d", fd);
> @@ -153,7 +157,7 @@ static void *mmap_populate(void *ptr, size_t size, int
> fd, bool shared, * If mmap failed with MAP_SHARED_VALIDATE | MAP_SYNC, we
> will try * again without these flags to handle backwards compatibility. */
> - new_ptr = mmap(ptr, size, PROT_READ | PROT_WRITE, flags, fd, 0);
> + new_ptr = mmap(ptr, size, PROT_READ | PROT_WRITE, flags, fd,
> fd_offset); }
> return new_ptr;
> }
> @@ -178,13 +182,16 @@ void *qemu_ram_mmap(int fd,
> size_t offset, total;
> void *ptr, *guardptr;
>
> + /* we can only map whole pages */
> + size = QEMU_ALIGN_UP(size, pagesize);
> +
Caller already rounds up size to block->page_size.
Why this QEMU_ALIGN_UP is necessary?
> /*
> * Note: this always allocates at least one extra page of virtual
> address * space, even if size is already aligned.
> */
> total = size + align;
If size was aligned above with pagesize boundary, why would this align be
necessary?
Can the pagesize differ from memory region align?
>
> - guardptr = mmap_reserve(total, fd);
> + guardptr = mmap_reserve(0, total, fd);
> if (guardptr == MAP_FAILED) {
> return MAP_FAILED;
> }
> @@ -195,7 +202,7 @@ void *qemu_ram_mmap(int fd,
>
> offset = QEMU_ALIGN_UP((uintptr_t)guardptr, align) -
> (uintptr_t)guardptr;
>
> - ptr = mmap_populate(guardptr + offset, size, fd, shared, is_pmem);
> + ptr = mmap_populate(guardptr + offset, size, fd, 0, shared, is_pmem);
> if (ptr == MAP_FAILED) {
> munmap(guardptr, total);
> return MAP_FAILED;
> @@ -221,6 +228,9 @@ void qemu_ram_munmap(int fd, void *ptr, size_t size)
> {
> const size_t pagesize = mmap_pagesize(fd);
>
> + /* we can only map whole pages */
> + size = QEMU_ALIGN_UP(size, pagesize);
> +
I'm trying to understand why this align is necessary, too.
> if (ptr) {
> /* Unmap both the RAM block and the guard page */
> munmap(ptr, size + pagesize);
--
Murilo
