diff mbox series

[1/6] migration/postcopy: reduce memset when it is zero page and matches_target_page_size

Message ID 20191018004850.9888-2-richardw.yang@linux.intel.com
State New
Headers show
Series migration/postcopy: enable compress during postcopy | expand

Commit Message

Wei Yang Oct. 18, 2019, 12:48 a.m. UTC 
In this case, page_buffer content would not be used.

Skip this to save some time.

Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
---
 migration/ram.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

Comments

Dr. David Alan Gilbert Nov. 6, 2019, 6:18 p.m. UTC | #1 
* Wei Yang (richardw.yang@linux.intel.com) wrote:
> In this case, page_buffer content would not be used.
> 
> Skip this to save some time.
> 
> Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
> ---
>  migration/ram.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/migration/ram.c b/migration/ram.c
> index 99a98b2da4..7938a643d9 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -4091,7 +4091,13 @@ static int ram_load_postcopy(QEMUFile *f)
>          switch (flags & ~RAM_SAVE_FLAG_CONTINUE) {
>          case RAM_SAVE_FLAG_ZERO:
>              ch = qemu_get_byte(f);
> -            memset(page_buffer, ch, TARGET_PAGE_SIZE);
> +            /*
> +             * Can skip to set page_buffer when
> +             * this is a zero page and (block->page_size == TARGET_PAGE_SIZE).
> +             */

When it's zero we will use place_page_zero which doesn't need
to page_buffer; so yes that's OK; and you're right, the gotcha is with 
mismatched page sizes where one subpage might be zero but not all of
them; so yes it's right that we need that check.

SO yes,


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

> +            if (ch || !matches_target_page_size) {
> +                memset(page_buffer, ch, TARGET_PAGE_SIZE);
> +            }
>              if (ch) {
>                  all_zero = false;
>              }
> -- 
> 2.17.1
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
diff mbox series

Patch

diff --git a/migration/ram.c b/migration/ram.c
index 99a98b2da4..7938a643d9 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -4091,7 +4091,13 @@  static int ram_load_postcopy(QEMUFile *f)
         switch (flags & ~RAM_SAVE_FLAG_CONTINUE) {
         case RAM_SAVE_FLAG_ZERO:
             ch = qemu_get_byte(f);
-            memset(page_buffer, ch, TARGET_PAGE_SIZE);
+            /*
+             * Can skip to set page_buffer when
+             * this is a zero page and (block->page_size == TARGET_PAGE_SIZE).
+             */
+            if (ch || !matches_target_page_size) {
+                memset(page_buffer, ch, TARGET_PAGE_SIZE);
+            }
             if (ch) {
                 all_zero = false;
             }