linux-kernel - [PATCH 3.16 210/294] mm/hugetlb: improve locking in dissolve_free_huge

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Message-ID: <lsq.1510009382.229599267@decadent.org.uk>
Date:   Mon, 06 Nov 2017 23:03:02 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "Mike Kravetz" <mike.kravetz@...cle.com>,
        "Michal Hocko" <mhocko@...e.com>,
        "Gerald Schaefer" <gerald.schaefer@...ibm.com>,
        "Dave Hansen" <dave.hansen@...ux.intel.com>,
        "Heiko Carstens" <heiko.carstens@...ibm.com>,
        "Rui Teng" <rui.teng@...ux.vnet.ibm.com>,
        "Linus Torvalds" <torvalds@...ux-foundation.org>,
        "Martin Schwidefsky" <schwidefsky@...ibm.com>,
        "Arnd Bergmann" <arnd@...db.de>,
        "Naoya Horiguchi" <n-horiguchi@...jp.nec.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        "Vlastimil Babka" <vbabka@...e.cz>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.vnet.ibm.com>
Subject: [PATCH 3.16 210/294] mm/hugetlb: improve locking in
 dissolve_free_huge_pages()

3.16.50-rc1 review patch.  If anyone has any objections, please let me know.

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

From: Gerald Schaefer <gerald.schaefer@...ibm.com>

commit eb03aa008561004257900983193d024e57abdd96 upstream.

For every pfn aligned to minimum_order, dissolve_free_huge_pages() will
call dissolve_free_huge_page() which takes the hugetlb spinlock, even if
the page is not huge at all or a hugepage that is in-use.

Improve this by doing the PageHuge() and page_count() checks already in
dissolve_free_huge_pages() before calling dissolve_free_huge_page().  In
dissolve_free_huge_page(), when holding the spinlock, those checks need
to be revalidated.

Link: http://lkml.kernel.org/r/20160926172811.94033-4-gerald.schaefer@de.ibm.com
Signed-off-by: Gerald Schaefer <gerald.schaefer@...ibm.com>
Acked-by: Michal Hocko <mhocko@...e.com>
Acked-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
Cc: "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
Cc: Vlastimil Babka <vbabka@...e.cz>
Cc: Mike Kravetz <mike.kravetz@...cle.com>
Cc: "Aneesh Kumar K . V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc: Martin Schwidefsky <schwidefsky@...ibm.com>
Cc: Heiko Carstens <heiko.carstens@...ibm.com>
Cc: Rui Teng <rui.teng@...ux.vnet.ibm.com>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Arnd Bergmann <arnd@...db.de>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 mm/hugetlb.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1105,14 +1105,20 @@ out:
 int dissolve_free_huge_pages(unsigned long start_pfn, unsigned long end_pfn)
 {
 	unsigned long pfn;
+	struct page *page;
 	int rc = 0;
 
 	if (!hugepages_supported())
 		return rc;
 
-	for (pfn = start_pfn; pfn < end_pfn; pfn += 1 << minimum_order)
-		if (rc = dissolve_free_huge_page(pfn_to_page(pfn)))
-			break;
+	for (pfn = start_pfn; pfn < end_pfn; pfn += 1 << minimum_order) {
+		page = pfn_to_page(pfn);
+		if (PageHuge(page) && !page_count(page)) {
+			rc = dissolve_free_huge_page(page);
+			if (rc)
+				break;
+		}
+	}
 
 	return rc;
 }