Re: [Xen-devel] [PATCH] docs: clarify xl mem-max semantics

[Jim Fehlig <jfehlig@xxxxxxxx>]

On 01/20/2017 02:54 AM, Juergen Gross wrote:
> The information given in the xl man page for the mem-max command is
> rather brief. Expand it in order to let the reader understand what it
> is really doing.
>
> As the related libxl function libxl_domain_setmaxmem() isn't much
> clearer add a comment to it explaining the desired semantics.
>
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> ---
>  docs/man/xl.pod.1.in | 10 ++++++++++
>  tools/libxl/libxl.c  |  6 ++++++
>  2 files changed, 16 insertions(+)
>
> diff --git a/docs/man/xl.pod.1.in b/docs/man/xl.pod.1.in
> index 09c1faa..62307e8 100644
> --- a/docs/man/xl.pod.1.in
> +++ b/docs/man/xl.pod.1.in
> @@ -401,6 +401,16 @@ for bytes.
>  The mem-max value may not correspond to the actual memory used in the
>  domain, as it may balloon down its memory to give more back to the OS.
>
> +The value given just sets the memory amount the domain is allowed to allocate
> +in the hypervisor. Thus it can't be lower than the current reservation, but
> +it is allowed to be higher than the configured maximum memory size of the
> +domain (B<maxmem> parameter in the domain's configuration). Setting the
> +allowed memory size via B<xl mem-max> above the B<maxmem> size won't let use
> +this value to be used for B<xl mem-set>, as B<xl mem-set> will still use
> +B<maxmem> as an upper limit.
I find the last sentence a bit awkward. Might I suggest

Using B<xl mem-max> to set the maximum memory above the initial B<maxmem> value 
will not allow the additional memory to be used via B<xl mem-set>. The initial 
B<maxmem> value is still used as an upper limit for B<xl mem-set>.
Regards,
Jim

> +
> +The domain is not receiving any signal regarding the changed memory limit.
> +
>  =item B<mem-set> I<domain-id> I<mem>
>
>  Set the domain's used memory using the balloon driver; append 't' for
> diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
> index 0622311..ed59510 100644
> --- a/tools/libxl/libxl.c
> +++ b/tools/libxl/libxl.c
> @@ -4018,6 +4018,12 @@ out:
>
>  
> /******************************************************************************/
>
> +/*
> + * Set the maximum memory size of the domain in the hypervisor. There is no
> + * change of the current memory size involved. The allowed memory size can
> + * even be above the configured maxmem size of the domain, but the related
> + * Xenstore entry memory/static-max isn't modified!
> + */
>  int libxl_domain_setmaxmem(libxl_ctx *ctx, uint32_t domid, uint64_t max_memkb)
>  {
>      GC_INIT(ctx);

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