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Subject[PATCH 3.19.y-ckt 206/251] mm/hugetlb: introduce minimum hugepage order
Date
3.19.8-ckt4 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>

commit 641844f5616d7c6597309f560838f996466d7aac upstream.

Currently the initial value of order in dissolve_free_huge_page is 64 or
32, which leads to the following warning in static checker:

mm/hugetlb.c:1203 dissolve_free_huge_pages()
warn: potential right shift more than type allows '9,18,64'

This is a potential risk of infinite loop, because 1 << order (== 0) is used
in for-loop like this:

for (pfn =3D start_pfn; pfn < end_pfn; pfn +=3D 1 << order)
...

So this patch fixes it by using global minimum_order calculated at boot time.

text data bss dec hex filename
28313 469 84236 113018 1b97a mm/hugetlb.o
28256 473 84236 112965 1b945 mm/hugetlb.o (patched)

Fixes: c8721bbbdd36 ("mm: memory-hotplug: enable memory hotplug to handle hugepage")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
mm/hugetlb.c | 19 +++++++++++--------
1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index a2bfd02..2870d90 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -40,6 +40,11 @@ unsigned long hugepages_treat_as_movable;
int hugetlb_max_hstate __read_mostly;
unsigned int default_hstate_idx;
struct hstate hstates[HUGE_MAX_HSTATE];
+/*
+ * Minimum page order among possible hugepage sizes, set to a proper value
+ * at boot time.
+ */
+static unsigned int minimum_order __read_mostly = UINT_MAX;

__initdata LIST_HEAD(huge_boot_pages);

@@ -1084,19 +1089,13 @@ static void dissolve_free_huge_page(struct page *page)
*/
void dissolve_free_huge_pages(unsigned long start_pfn, unsigned long end_pfn)
{
- unsigned int order = 8 * sizeof(void *);
unsigned long pfn;
- struct hstate *h;

if (!hugepages_supported())
return;

- /* Set scan step to minimum hugepage size */
- for_each_hstate(h)
- if (order > huge_page_order(h))
- order = huge_page_order(h);
- VM_BUG_ON(!IS_ALIGNED(start_pfn, 1 << order));
- for (pfn = start_pfn; pfn < end_pfn; pfn += 1 << order)
+ VM_BUG_ON(!IS_ALIGNED(start_pfn, 1 << minimum_order));
+ for (pfn = start_pfn; pfn < end_pfn; pfn += 1 << minimum_order)
dissolve_free_huge_page(pfn_to_page(pfn));
}

@@ -1523,10 +1522,14 @@ static void __init hugetlb_init_hstates(void)
struct hstate *h;

for_each_hstate(h) {
+ if (minimum_order > huge_page_order(h))
+ minimum_order = huge_page_order(h);
+
/* oversize hugepages were init'ed in early boot */
if (!hstate_is_gigantic(h))
hugetlb_hstate_alloc_pages(h);
}
+ VM_BUG_ON(minimum_order == UINT_MAX);
}

static char * __init memfmt(char *buf, unsigned long n)
--
1.9.1


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