linux-kernel - [PATCH 3.19.y-ckt 206/251] mm/hugetlb: introduce minimum hugepage order

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Message-Id: <1437008972-9140-207-git-send-email-kamal@canonical.com>
Date:	Wed, 15 Jul 2015 18:08:47 -0700
From:	Kamal Mostafa <kamal@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Kamal Mostafa <kamal@...onical.com>
Subject: [PATCH 3.19.y-ckt 206/251] mm/hugetlb: introduce minimum hugepage order

3.19.8-ckt4 -stable review patch.  If anyone has any objections, please let me know.

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

From: Naoya Horiguchi <n-horiguchi@...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@...cle.com>
Signed-off-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Kamal Mostafa <kamal@...onical.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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