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Patch "mm/hugetlb: introduce minimum hugepage order" has been added to the 4.1-stable tree

PATCH [email protected] 1 participant 1 message Jul 31, 2015

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This is a note to let you know that I've just added the patch titled

mm/hugetlb: introduce minimum hugepage order

to the 4.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
mm-hugetlb-introduce-minimum-hugepage-order.patch
and it can be found in the queue-4.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

Quoted 1 line

From 641844f5616d7c6597309f560838f996466d7aac Mon Sep 17 00:00:00 2001

From: Naoya Horiguchi <[email protected]>
Date: Wed, 24 Jun 2015 16:56:59 -0700
Subject: mm/hugetlb: introduce minimum hugepage order

From: Naoya Horiguchi <[email protected]>

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 <[email protected]>
Signed-off-by Naoya Horiguchi <[email protected]>
Signed-off-by Andrew Morton <[email protected]>
Signed-off-by Linus Torvalds <[email protected]>
Signed-off-by Greg Kroah-Hartman <[email protected]>
---
 mm/hugetlb.c |   19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)
mm/hugetlb.c +11 -8
@@ -40,6 +40,11 @@ int 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);
 

@@ -1188,19 +1193,13 @@ static void dissolve_free_huge_page(stru
  */
 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));
 }
 

@@ -1627,10 +1626,14 @@ static void __init hugetlb_init_hstates(
 	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)

Patches currently in stable-queue which might be from [email protected] are

queue-4.1/mm-hugetlb-introduce-minimum-hugepage-order.patch