Re: [Qemu-devel] [PATCH 4/5] memory: Add 'persistent' parameter to memory_region_init_ram_from_file()

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Eduardo Habkost (ehabkost@redhat.com) wrote:
> Make it possible to set the RAM_NONPERSISTENT flag on the RAMBlock when
> mapping a file.
> 
> Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

A little confusing having a persistent flag passed in but setting a
NONPERSISTENT flag.

One thing to watch out for is the other effect, for example I think
doing an MADV_REMOVE will zero the file;  if that's a ROM file that
would probably be bad; but your description of persistent=false
might make sense for a ROM file since it wont be changed.

Dave

> ---
>  include/exec/memory.h   | 4 ++++
>  include/exec/ram_addr.h | 4 ++--
>  backends/hostmem-file.c | 2 +-
>  exec.c                  | 7 +++++--
>  memory.c                | 4 +++-
>  numa.c                  | 2 +-
>  6 files changed, 16 insertions(+), 7 deletions(-)
> 
> diff --git a/include/exec/memory.h b/include/exec/memory.h
> index 80e605a96a..f47c534179 100644
> --- a/include/exec/memory.h
> +++ b/include/exec/memory.h
> @@ -446,6 +446,9 @@ void memory_region_init_resizeable_ram(MemoryRegion *mr,
>   *        must be unique within any device
>   * @size: size of the region.
>   * @share: %true if memory must be mmaped with the MAP_SHARED flag
> + * @persistent: %false if RAM contents can be discarded and don't
> + *              need to be flushed to disk when the memory region
> + *              is freed.
>   * @path: the path in which to allocate the RAM.
>   * @errp: pointer to Error*, to store an error if it happens.
>   */
> @@ -454,6 +457,7 @@ void memory_region_init_ram_from_file(MemoryRegion *mr,
>                                        const char *name,
>                                        uint64_t size,
>                                        bool share,
> +                                      bool persistent,
>                                        const char *path,
>                                        Error **errp);
>  #endif
> diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
> index 140efa840c..67dc099355 100644
> --- a/include/exec/ram_addr.h
> +++ b/include/exec/ram_addr.h
> @@ -63,8 +63,8 @@ static inline void *ramblock_ptr(RAMBlock *block, ram_addr_t offset)
>  long qemu_getrampagesize(void);
>  unsigned long last_ram_page(void);
>  RAMBlock *qemu_ram_alloc_from_file(ram_addr_t size, MemoryRegion *mr,
> -                                   bool share, const char *mem_path,
> -                                   Error **errp);
> +                                   bool share, bool persistent,
> +                                   const char *mem_path, Error **errp);
>  RAMBlock *qemu_ram_alloc_from_ptr(ram_addr_t size, void *host,
>                                    MemoryRegion *mr, Error **errp);
>  RAMBlock *qemu_ram_alloc(ram_addr_t size, MemoryRegion *mr, Error **errp);
> diff --git a/backends/hostmem-file.c b/backends/hostmem-file.c
> index fc4ef46d11..d078775b4b 100644
> --- a/backends/hostmem-file.c
> +++ b/backends/hostmem-file.c
> @@ -57,7 +57,7 @@ file_backend_memory_alloc(HostMemoryBackend *backend, Error **errp)
>          path = object_get_canonical_path(OBJECT(backend));
>          memory_region_init_ram_from_file(&backend->mr, OBJECT(backend),
>                                   path,
> -                                 backend->size, fb->share,
> +                                 backend->size, fb->share, true,
>                                   fb->mem_path, errp);
>          g_free(path);
>      }
> diff --git a/exec.c b/exec.c
> index a6e9ed4ece..77734198d0 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -1937,8 +1937,8 @@ static void ram_block_add(RAMBlock *new_block, Error **errp)
>  
>  #ifdef __linux__
>  RAMBlock *qemu_ram_alloc_from_file(ram_addr_t size, MemoryRegion *mr,
> -                                   bool share, const char *mem_path,
> -                                   Error **errp)
> +                                   bool share, bool persistent,
> +                                   const char *mem_path, Error **errp)
>  {
>      RAMBlock *new_block;
>      Error *local_err = NULL;
> @@ -1965,6 +1965,9 @@ RAMBlock *qemu_ram_alloc_from_file(ram_addr_t size, MemoryRegion *mr,
>      new_block->used_length = size;
>      new_block->max_length = size;
>      new_block->flags = share ? RAM_SHARED : 0;
> +    if (!persistent) {
> +        new_block->flags |= RAM_NONPERSISTENT;
> +    }
>      new_block->host = file_ram_alloc(new_block, size,
>                                       mem_path, errp);
>      if (!new_block->host) {
> diff --git a/memory.c b/memory.c
> index 0ddc4cc28d..3c0c0ff141 100644
> --- a/memory.c
> +++ b/memory.c
> @@ -1387,6 +1387,7 @@ void memory_region_init_ram_from_file(MemoryRegion *mr,
>                                        const char *name,
>                                        uint64_t size,
>                                        bool share,
> +                                      bool persistent,
>                                        const char *path,
>                                        Error **errp)
>  {
> @@ -1394,7 +1395,8 @@ void memory_region_init_ram_from_file(MemoryRegion *mr,
>      mr->ram = true;
>      mr->terminates = true;
>      mr->destructor = memory_region_destructor_ram;
> -    mr->ram_block = qemu_ram_alloc_from_file(size, mr, share, path, errp);
> +    mr->ram_block = qemu_ram_alloc_from_file(size, mr, share, persistent,
> +                                             path, errp);
>      mr->dirty_log_mask = tcg_enabled() ? (1 << DIRTY_MEMORY_CODE) : 0;
>  }
>  #endif
> diff --git a/numa.c b/numa.c
> index 65701cb6c8..825d5933ca 100644
> --- a/numa.c
> +++ b/numa.c
> @@ -531,7 +531,7 @@ static void allocate_system_memory_nonnuma(MemoryRegion *mr, Object *owner,
>      if (mem_path) {
>  #ifdef __linux__
>          Error *err = NULL;
> -        memory_region_init_ram_from_file(mr, owner, name, ram_size, false,
> +        memory_region_init_ram_from_file(mr, owner, name, ram_size, false, true,
>                                           mem_path, &err);
>          if (err) {
>              error_report_err(err);
> -- 
> 2.11.0.259.g40922b1
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK