Re: [PATCH] mm: make transparent hugepage size public

[Michal Hocko <mhocko@suse.com>]

On Mon 05-12-16 22:05:22, Hugh Dickins wrote:
> Test programs want to know the size of a transparent hugepage.
> While it is commonly the same as the size of a hugetlbfs page
> (shown as Hugepagesize in /proc/meminfo), that is not always so:
> powerpc implements transparent hugepages in a different way from
> hugetlbfs pages, so it's coincidence when their sizes are the same;
> and x86 and others can support more than one hugetlbfs page size.
> 
> Add /sys/kernel/mm/transparent_hugepage/hpage_pmd_size to show the
> THP size in bytes - it's the same for Anonymous and Shmem hugepages.
> Call it hpage_pmd_size (after HPAGE_PMD_SIZE) rather than hpage_size,
> in case some transparent support for pud and pgd pages is added later.

Definitely much better than cluttering /proc/meminfo even more.

> Signed-off-by: Hugh Dickins <hughd@google.com>

Acked-by: Michal Hocko <mhocko@suse.com>

> ---
> 
>  Documentation/vm/transhuge.txt |    5 +++++
>  mm/huge_memory.c               |   10 ++++++++++
>  2 files changed, 15 insertions(+)
> 
> --- 4.9-rc8/Documentation/vm/transhuge.txt	2016-10-02 16:24:33.000000000 -0700
> +++ linux/Documentation/vm/transhuge.txt	2016-12-05 20:55:12.142578631 -0800
> @@ -136,6 +136,11 @@ or enable it back by writing 1:
>  echo 0 >/sys/kernel/mm/transparent_hugepage/use_zero_page
>  echo 1 >/sys/kernel/mm/transparent_hugepage/use_zero_page
>  
> +Some userspace (such as a test program, or an optimized memory allocation
> +library) may want to know the size (in bytes) of a transparent hugepage:
> +
> +cat /sys/kernel/mm/transparent_hugepage/hpage_pmd_size
> +
>  khugepaged will be automatically started when
>  transparent_hugepage/enabled is set to "always" or "madvise, and it'll
>  be automatically shutdown if it's set to "never".
> --- 4.9-rc8/mm/huge_memory.c	2016-12-04 16:42:39.881703357 -0800
> +++ linux/mm/huge_memory.c	2016-12-05 20:58:19.953010005 -0800
> @@ -285,6 +285,15 @@ static ssize_t use_zero_page_store(struc
>  }
>  static struct kobj_attribute use_zero_page_attr =
>  	__ATTR(use_zero_page, 0644, use_zero_page_show, use_zero_page_store);
> +
> +static ssize_t hpage_pmd_size_show(struct kobject *kobj,
> +		struct kobj_attribute *attr, char *buf)
> +{
> +	return sprintf(buf, "%lu\n", HPAGE_PMD_SIZE);
> +}
> +static struct kobj_attribute hpage_pmd_size_attr =
> +	__ATTR_RO(hpage_pmd_size);
> +
>  #ifdef CONFIG_DEBUG_VM
>  static ssize_t debug_cow_show(struct kobject *kobj,
>  				struct kobj_attribute *attr, char *buf)
> @@ -307,6 +316,7 @@ static struct attribute *hugepage_attr[]
>  	&enabled_attr.attr,
>  	&defrag_attr.attr,
>  	&use_zero_page_attr.attr,
> +	&hpage_pmd_size_attr.attr,
>  #if defined(CONFIG_SHMEM) && defined(CONFIG_TRANSPARENT_HUGE_PAGECACHE)
>  	&shmem_enabled_attr.attr,
>  #endif
> 
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-- 
Michal Hocko
SUSE Labs

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