[PATCH v3] docs: clarify xl mem-max semantics

[PATCH v3] docs: clarify xl mem-max semantics

[Juergen Gross]

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>
---
V3: more rewording as suggested by Jim Fehlig
V2: rewording as suggested by Jim Fehlig and Ian Jackson
---
 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..7caed08 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. It can't be set 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). 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>.
+
+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..d400fa2 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 specified 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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Re: [PATCH v3] docs: clarify xl mem-max semantics

[Wei Liu]

On Fri, Jan 27, 2017 at 12:45:18PM +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.
> 
> Signed-off-by: Juergen Gross <jgross@suse.com>

Acked + applied.

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