* [PATCH] docs: clarify xl mem-max semantics
@ 2017-01-20 9:54 Juergen Gross
2017-01-20 13:48 ` Konrad Rzeszutek Wilk
2017-01-20 23:15 ` Jim Fehlig
0 siblings, 2 replies; 6+ messages in thread
From: Juergen Gross @ 2017-01-20 9:54 UTC (permalink / raw)
To: xen-devel; +Cc: Juergen Gross, wei.liu2, ian.jackson
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@suse.com>
---
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.
+
+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);
--
2.10.2
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^ permalink raw reply related [flat|nested] 6+ messages in thread* Re: [PATCH] docs: clarify xl mem-max semantics
2017-01-20 9:54 [PATCH] docs: clarify xl mem-max semantics Juergen Gross
@ 2017-01-20 13:48 ` Konrad Rzeszutek Wilk
2017-01-20 15:51 ` Ian Jackson
2017-01-20 23:15 ` Jim Fehlig
1 sibling, 1 reply; 6+ messages in thread
From: Konrad Rzeszutek Wilk @ 2017-01-20 13:48 UTC (permalink / raw)
To: Juergen Gross, daniel.kiper; +Cc: xen-devel, wei.liu2, ian.jackson
On Fri, Jan 20, 2017 at 10:54:18AM +0100, 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.
CC-ing Daniel
>
> Signed-off-by: Juergen Gross <jgross@suse.com>
> ---
> 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.
> +
> +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);
> --
> 2.10.2
>
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org
> https://lists.xen.org/xen-devel
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^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH] docs: clarify xl mem-max semantics
2017-01-20 13:48 ` Konrad Rzeszutek Wilk
@ 2017-01-20 15:51 ` Ian Jackson
2017-01-20 16:13 ` Juergen Gross
0 siblings, 1 reply; 6+ messages in thread
From: Ian Jackson @ 2017-01-20 15:51 UTC (permalink / raw)
To: Konrad Rzeszutek Wilk; +Cc: Juergen Gross, xen-devel, daniel.kiper, wei.liu2
Konrad Rzeszutek Wilk writes ("Re: [Xen-devel] [PATCH] docs: clarify xl mem-max semantics"):
> On Fri, Jan 20, 2017 at 10:54:18AM +0100, Juergen Gross wrote:
> > 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.
Thanks for working on this.
> > +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,
This is not true. It is perfectly possible to set max_pages lower
than the current reservation. This is routine: xl mem-set does it
when the guest is being asked to shrink. It prevents the guest from
growing instead.
Setting max_pages < target seems like it wouldn't make sense but as I
don't understand the system setup for target != max_pages I don't feel
confident about that.
> > + * 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!
static-max is an "almost unrelated" entry, not a "related" one.
Ian.
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^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH] docs: clarify xl mem-max semantics
2017-01-20 15:51 ` Ian Jackson
@ 2017-01-20 16:13 ` Juergen Gross
0 siblings, 0 replies; 6+ messages in thread
From: Juergen Gross @ 2017-01-20 16:13 UTC (permalink / raw)
To: Ian Jackson, Konrad Rzeszutek Wilk; +Cc: xen-devel, daniel.kiper, wei.liu2
On 20/01/17 16:51, Ian Jackson wrote:
> Konrad Rzeszutek Wilk writes ("Re: [Xen-devel] [PATCH] docs: clarify xl mem-max semantics"):
>> On Fri, Jan 20, 2017 at 10:54:18AM +0100, Juergen Gross wrote:
>>> 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.
>
> Thanks for working on this.
>
>>> +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,
>
> This is not true. It is perfectly possible to set max_pages lower
> than the current reservation. This is routine: xl mem-set does it
> when the guest is being asked to shrink. It prevents the guest from
> growing instead.
>
> Setting max_pages < target seems like it wouldn't make sense but as I
> don't understand the system setup for target != max_pages I don't feel
> confident about that.
xl mem-max won't let you set the value below current reservation.
There is an explicit test in libxl_domain_setmaxmem() to deny such an
attempt.
You are right, however, that there is no causal link between above two
sentences as the wording implies. I'll rephrase that part.
>>> + * 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!
>
> static-max is an "almost unrelated" entry, not a "related" one.
static-max is related to maxmem. It isn't really related to max_pages.
Juergen
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^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] docs: clarify xl mem-max semantics
2017-01-20 9:54 [PATCH] docs: clarify xl mem-max semantics Juergen Gross
2017-01-20 13:48 ` Konrad Rzeszutek Wilk
@ 2017-01-20 23:15 ` Jim Fehlig
2017-01-23 6:07 ` Juergen Gross
1 sibling, 1 reply; 6+ messages in thread
From: Jim Fehlig @ 2017-01-20 23:15 UTC (permalink / raw)
To: Juergen Gross, xen-devel; +Cc: ian.jackson, wei.liu2
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@suse.com>
> ---
> 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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^ permalink raw reply [flat|nested] 6+ messages in thread* Re: [PATCH] docs: clarify xl mem-max semantics
2017-01-20 23:15 ` Jim Fehlig
@ 2017-01-23 6:07 ` Juergen Gross
0 siblings, 0 replies; 6+ messages in thread
From: Juergen Gross @ 2017-01-23 6:07 UTC (permalink / raw)
To: Jim Fehlig, xen-devel; +Cc: ian.jackson, wei.liu2
On 21/01/17 00:15, Jim Fehlig wrote:
> 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@suse.com>
>> ---
>> 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>.
Yes, this is better.
Thanks,
Juergen
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^ permalink raw reply [flat|nested] 6+ messages in thread
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2017-01-20 9:54 [PATCH] docs: clarify xl mem-max semantics Juergen Gross
2017-01-20 13:48 ` Konrad Rzeszutek Wilk
2017-01-20 15:51 ` Ian Jackson
2017-01-20 16:13 ` Juergen Gross
2017-01-20 23:15 ` Jim Fehlig
2017-01-23 6:07 ` Juergen Gross
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