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. Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx> --- 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>