Re: [PATCH v4 11/15] util/mmap-alloc: Implement resizeable mmaps

["Murilo Opsfelder Araújo" <muriloo@linux.ibm.com>]

On Thursday, March 5, 2020 11:29:41 AM -03 David Hildenbrand wrote:
> Implement resizeable mmaps. For now, the actual resizing is not wired up.
> Introduce qemu_ram_mmap_resizeable() and qemu_ram_mmap_resize(). Make
> qemu_ram_mmap() a wrapper of qemu_ram_mmap_resizeable().
>
> Reviewed-by: Peter Xu <peterx@redhat.com>
> Cc: Richard Henderson <richard.henderson@linaro.org>
> Cc: Igor Kotrasinski <i.kotrasinsk@partner.samsung.com>
> Cc: Murilo Opsfelder Araujo <muriloo@linux.ibm.com>
> Cc: "Michael S. Tsirkin" <mst@redhat.com>
> Cc: Greg Kurz <groug@kaod.org>
> Cc: Eduardo Habkost <ehabkost@redhat.com>
> Cc: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> Cc: Igor Mammedov <imammedo@redhat.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---

Acked-by: Murilo Opsfelder Araujo <muriloo@linux.ibm.com>

>  include/qemu/mmap-alloc.h | 21 +++++++++++--------
>  util/mmap-alloc.c         | 43 ++++++++++++++++++++++++++++-----------
>  2 files changed, 44 insertions(+), 20 deletions(-)
>
> diff --git a/include/qemu/mmap-alloc.h b/include/qemu/mmap-alloc.h
> index e786266b92..ca8f7edf70 100644
> --- a/include/qemu/mmap-alloc.h
> +++ b/include/qemu/mmap-alloc.h
> @@ -7,11 +7,13 @@ size_t qemu_fd_getpagesize(int fd);
>  size_t qemu_mempath_getpagesize(const char *mem_path);
>
>  /**
> - * qemu_ram_mmap: mmap the specified file or device.
> + * qemu_ram_mmap_resizeable: reserve a memory region of @max_size to mmap
> the + *                           specified file or device and mmap @size
> of it. *
>   * Parameters:
>   *  @fd: the file or the device to mmap
>   *  @size: the number of bytes to be mmaped
> + *  @max_size: the number of bytes to be reserved
>   *  @align: if not zero, specify the alignment of the starting mapping
> address; *          otherwise, the alignment in use will be determined by
> QEMU. *  @shared: map has RAM_SHARED flag.
> @@ -21,12 +23,15 @@ size_t qemu_mempath_getpagesize(const char *mem_path);
>   *  On success, return a pointer to the mapped area.
>   *  On failure, return MAP_FAILED.
>   */
> -void *qemu_ram_mmap(int fd,
> -                    size_t size,
> -                    size_t align,
> -                    bool shared,
> -                    bool is_pmem);
> -
> -void qemu_ram_munmap(int fd, void *ptr, size_t size);
> +void *qemu_ram_mmap_resizeable(int fd, size_t size, size_t max_size,
> +                              size_t align, bool shared, bool is_pmem);
> +bool qemu_ram_mmap_resize(void *ptr, int fd, size_t old_size, size_t
> new_size, +                          bool shared, bool is_pmem);
> +static inline void *qemu_ram_mmap(int fd, size_t size, size_t align,
> +                                  bool shared, bool is_pmem)
> +{
> +    return qemu_ram_mmap_resizeable(fd, size, size, align, shared,
> is_pmem); +}
> +void qemu_ram_munmap(int fd, void *ptr, size_t max_size);
>
>  #endif
> diff --git a/util/mmap-alloc.c b/util/mmap-alloc.c
> index 2767caa33b..7ed85f16d3 100644
> --- a/util/mmap-alloc.c
> +++ b/util/mmap-alloc.c
> @@ -174,11 +174,8 @@ static inline size_t mmap_guard_pagesize(int fd)
>  #endif
>  }
>
> -void *qemu_ram_mmap(int fd,
> -                    size_t size,
> -                    size_t align,
> -                    bool shared,
> -                    bool is_pmem)
> +void *qemu_ram_mmap_resizeable(int fd, size_t size, size_t max_size,
> +                               size_t align, bool shared, bool is_pmem)
>  {
>      const size_t guard_pagesize = mmap_guard_pagesize(fd);
>      const size_t pagesize = qemu_fd_getpagesize(fd);
> @@ -186,12 +183,14 @@ void *qemu_ram_mmap(int fd,
>      void *ptr, *guardptr;
>
>      g_assert(QEMU_IS_ALIGNED(size, pagesize));
> +    g_assert(QEMU_IS_ALIGNED(max_size, pagesize));
>
>      /*
>       * Note: this always allocates at least one extra page of virtual
> address -     * space, even if size is already aligned.
> +     * space, even if the size is already aligned. We will reserve an area
> of +     * at least max_size, but only activate the requested part of it.
> */
> -    total = size + align;
> +    total = max_size + align;
>
>      guardptr = mmap_reserve(NULL, total, fd);
>      if (guardptr == MAP_FAILED) {
> @@ -219,21 +218,41 @@ void *qemu_ram_mmap(int fd,
>       * a guard page guarding against potential buffer overflows.
>       */
>      total -= offset;
> -    if (total > size + guard_pagesize) {
> -        munmap(ptr + size + guard_pagesize, total - size - guard_pagesize);
> +    if (total > max_size + guard_pagesize) {
> +        munmap(ptr + max_size + guard_pagesize,
> +               total - max_size - guard_pagesize);
>      }
>
>      return ptr;
>  }
>
> -void qemu_ram_munmap(int fd, void *ptr, size_t size)
> +bool qemu_ram_mmap_resize(void *ptr, int fd, size_t old_size, size_t
> new_size, +                          bool shared, bool is_pmem)
>  {
>      const size_t pagesize = qemu_fd_getpagesize(fd);
>
> -    g_assert(QEMU_IS_ALIGNED(size, pagesize));
> +    g_assert(QEMU_IS_ALIGNED(old_size, pagesize));
> +    g_assert(QEMU_IS_ALIGNED(new_size, pagesize));
> +
> +    if (old_size < new_size) {
> +        /* activate the missing piece in the reserved area */
> +        ptr = mmap_activate(ptr + old_size, new_size - old_size, fd,
> old_size, +                            shared, is_pmem);
> +    } else if (old_size > new_size) {
> +        /* discard this piece, marking it reserved */
> +        ptr = mmap_reserve(ptr + new_size, old_size - new_size, fd);
> +    }
> +    return ptr != MAP_FAILED;
> +}
> +
> +void qemu_ram_munmap(int fd, void *ptr, size_t max_size)
> +{
> +    const size_t pagesize = qemu_fd_getpagesize(fd);
> +
> +    g_assert(QEMU_IS_ALIGNED(max_size, pagesize));
>
>      if (ptr) {
>          /* Unmap both the RAM block and the guard page */
> -        munmap(ptr, size + mmap_guard_pagesize(fd));
> +        munmap(ptr, max_size + mmap_guard_pagesize(fd));
>      }
>  }


--
Murilo