Re: [Qemu-devel] [PATCH v12 8/9] qcow2: Set the default cache-clean-interval to 10 minutes

[Eric Blake]

On 9/26/18 11:04 AM, Leonid Bloch wrote:
> The default cache-clean-interval is set to 10 minutes, in order to lower
> the overhead of the qcow2 caches (before the default was 0, i.e.
> disabled).
>
> * For non-Linux platforms the default is kept at 0, because
>    cache-clean-interval is not supported there yet.
>
> Signed-off-by: Leonid Bloch <address@hidden>
> Reviewed-by: Alberto Garcia <address@hidden>
> Reviewed-by: Kevin Wolf <address@hidden>
> ---

> @@ -76,13 +76,15 @@
>   
>   #ifdef CONFIG_LINUX
>   #define DEFAULT_L2_CACHE_MAX_SIZE S_32MiB
> +#define DEFAULT_CACHE_CLEAN_INTERVAL 600  /* seconds */
>   #else
>   #define DEFAULT_L2_CACHE_MAX_SIZE S_8MiB
> +/* Cache clean interval is currently available only on Linux, so must be 0 */
> +#define DEFAULT_CACHE_CLEAN_INTERVAL 0
>   #endif
>   

> +++ b/docs/qcow2-cache.txt
> @@ -210,8 +210,8 @@ This example removes all unused cache entries every 15 
> minutes:
>   
>      -drive file=hd.qcow2,cache-clean-interval=900
>   
> -If unset, the default value for this parameter is 0 and it disables
> -this feature.
> +If unset, the default value for this parameter is 600. Setting it to 0
> +disables this feature.

Should this wording mention that the non-zero default is only on Linux 
(or rather, only on platforms where a non-zero value makes a difference)?

>   
>   Note that this functionality currently relies on the MADV_DONTNEED
>   argument for madvise() to actually free the memory. This is a
> diff --git a/qapi/block-core.json b/qapi/block-core.json
> index ac3b48ee54..46dac23d2f 100644
> --- a/qapi/block-core.json
> +++ b/qapi/block-core.json
> @@ -2895,7 +2895,8 @@
>   #
>   # @cache-clean-interval:  clean unused entries in the L2 and refcount
>   #                         caches. The interval is in seconds. The default 
> value
> -#                         is 0 and it disables this feature (since 2.5)
> +#                         is 600, and 0 disables this feature. (since 2.5)

and again here

> +#
>   # @encrypt:               Image decryption options. Mandatory for
>   #                         encrypted images, except when doing a metadata-only
>   #                         probe of the image. (since 2.10)
> diff --git a/qemu-options.hx b/qemu-options.hx
> index 14aee78c6c..52d9d9f06d 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -747,7 +747,7 @@ it which is not used for the L2 cache)
>   
>   @item cache-clean-interval
>   Clean unused entries in the L2 and refcount caches. The interval is in 
> seconds.
> -The default value is 0 and it disables this feature.
> +The default value is 600. Setting it to 0 disables this feature.

and here?

--
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org