Re: [PATCH] mm/hugetlb: fix total hugetlbfs pages count when memory overcommit accouting

[Wanpeng Li <liwanp@linux.vnet.ibm.com>]

On Thu, Mar 14, 2013 at 10:44:19AM +0100, Michal Hocko wrote:
>On Wed 13-03-13 15:08:31, Wanpeng Li wrote:
>> After commit 42d7395f ("mm: support more pagesizes for MAP_HUGETLB/SHM_HUGETLB")
>> be merged, kernel permit multiple huge page sizes,
>

Hi Michal,

>multiple huge page sizes were possible long before this commit. The
>above mentioned patch just made their usage via IPC much easier. You
>could do the same previously (since a137e1cc) by mounting hugetlbfs with
>a specific page size as a parameter and using mmap.
>

Agreed.

>> and when the system administrator has configured the system to provide
>> huge page pools of different sizes, application can choose the page
>> size used for their allocation.
>
>> However, just default size of huge page pool is statistical when
>> memory overcommit accouting, the bad is that this will result in
>> innocent processes be killed by oom-killer later.
>
>Why would an innnocent process be killed? The overcommit calculation
>is incorrect, that is true, but this just means that an unexpected
>ENOMEM/EFAULT or SIGSEGV would be returned, no? How an OOM could be a
>result?

Agreed.

>
>> Fix it by statistic all huge page pools of different sizes provided by
>> administrator.
>
>The patch makes sense but the description is misleading AFAICS.
>

Thanks for your pointing out Michal, I will update the description. :-)

Regards,
Wanpeng Li 

>> Testcase:
>> boot: hugepagesz=1G hugepages=1
>> before patch:
>> egrep 'CommitLimit' /proc/meminfo
>> CommitLimit:     55434168 kB
>> after patch:
>> egrep 'CommitLimit' /proc/meminfo
>> CommitLimit:     54909880 kB
>> 
>> Signed-off-by: Wanpeng Li <liwanp@linux.vnet.ibm.com>
>> ---
>>  mm/hugetlb.c | 7 +++++--
>>  1 file changed, 5 insertions(+), 2 deletions(-)
>> 
>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>> index cdb64e4..9e25040 100644
>> --- a/mm/hugetlb.c
>> +++ b/mm/hugetlb.c
>> @@ -2124,8 +2124,11 @@ int hugetlb_report_node_meminfo(int nid, char *buf)
>>  /* Return the number pages of memory we physically have, in PAGE_SIZE units. */
>>  unsigned long hugetlb_total_pages(void)
>>  {
>> -	struct hstate *h = &default_hstate;
>> -	return h->nr_huge_pages * pages_per_huge_page(h);
>> +	struct hstate *h;
>> +	unsigned long nr_total_pages = 0;
>> +	for_each_hstate(h)
>> +		nr_total_pages += h->nr_huge_pages * pages_per_huge_page(h);
>> +	return nr_total_pages;
>>  }
>>  
>>  static int hugetlb_acct_memory(struct hstate *h, long delta)
>> -- 
>> 1.7.11.7
>> 
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>
>-- 
>Michal Hocko
>SUSE Labs

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