[libvirt] [PATCH 1/3] virNumaGetPageInfo: Take huge pages into account

[Ján Tomko]

On 06/23/2014 03:59 PM, Michal Privoznik wrote:
> On the Linux kernel, if huge pages are allocated the size they cut off
> from memory is accounted under the 'MemUsed' in the meminfo file.
> However, we want the sum to be subtracted from 'MemTotal'. This patch
> implements this feature. After this change, we can enable reporting
> of the ordinary system pages in the capability XML:
> 
> <capabilities>
> 
>   <host>
>     <uuid>01281cda-f352-cb11-a9db-e905fe22010c</uuid>
>     <cpu>
>       <arch>x86_64</arch>
>       <model>Haswell</model>
>       <vendor>Intel</vendor>
>       <topology sockets='1' cores='1' threads='1'/>
>       <feature/>
>       <pages unit='KiB' size='4'/>
>       <pages unit='KiB' size='2048'/>
>       <pages unit='KiB' size='1048576'/>
>     </cpu>
>     <power_management/>
>     <migration_features/>
>     <topology>
>       <cells num='4'>
>         <cell id='0'>
>           <memory unit='KiB'>4048248</memory>
>           <pages unit='KiB' size='4'>748382</pages>
>           <pages unit='KiB' size='2048'>3</pages>
>           <pages unit='KiB' size='1048576'>1</pages>
>           <distances/>
>           <cpus num='1'>
>             <cpu id='0' socket_id='0' core_id='0' siblings='0'/>
>           </cpus>
>         </cell>
>         ...
>       </cells>
>     </topology>
>   </host>
> </capabilities>
> 
> You can see the beautiful thing about this: if you sum up all the
> <pages/> you'll get <memory/>.
> 
> Signed-off-by: Michal Privoznik <mprivozn at redhat.com>
> ---
>  src/nodeinfo.c     |  2 +-
>  src/util/virnuma.c | 65 +++++++++++++++++++++++++++++++-----------------------
>  src/util/virnuma.h |  1 +
>  3 files changed, 39 insertions(+), 29 deletions(-)
> 

> @@ -647,6 +649,13 @@ virNumaGetHugePageInfo(int node,
>   * total number of pages in the pool (both free and taken)
>   * and count for free pages in the pool.
>   *
> + * The @huge_page_sum parameter exists there due to the Linux

s/there//

> + * kernel limitation. The problem is, if there are some huge
> + * pages allocated, they are accounted under the 'MemUsed' field
> + * in the meminfo file instead of being subtracted from the
> + * 'MemTotal'. We must do the subtraction ourselves.
> + * If unsure, pass 0.
> + *
>   * If you're interested in just one bit, pass NULL to the other one.
>   *
>   * As a special case, if @node == -1, overall info is fetched
> @@ -657,6 +666,7 @@ virNumaGetHugePageInfo(int node,
>  int
>  virNumaGetPageInfo(int node,
>                     unsigned int page_size,
> +                   unsigned long long huge_page_sum,
>                     unsigned int *page_avail,
>                     unsigned int *page_free)
>  {
> @@ -666,7 +676,6 @@ virNumaGetPageInfo(int node,
>      /* sysconf() returns page size in bytes,
>       * the @page_size is however in kibibytes */
>      if (page_size == system_page_size / 1024) {
> -# if 0
>          unsigned long long memsize, memfree;
>  
>          /* TODO: come up with better algorithm that takes huge pages into
> @@ -679,16 +688,14 @@ virNumaGetPageInfo(int node,
>                  goto cleanup;
>          }
>  
> +        /* see description above */

I think you can just move the comment above here.

> +        memsize -= huge_page_sum;
> +
>          if (page_avail)
>              *page_avail = memsize / system_page_size;
>  
>          if (page_free)
>              *page_free = memfree / system_page_size;

ACK

Jan

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