linux-kernel - [PATCH, RFC 5/6] mm: make clear_huge_page cache clear only around the fault address

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Message-Id: <1342788622-10290-6-git-send-email-kirill.shutemov@linux.intel.com>
Date:	Fri, 20 Jul 2012 15:50:21 +0300
From:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:	linux-mm@...ck.org
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	Andi Kleen <ak@...ux.intel.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Tim Chen <tim.c.chen@...ux.intel.com>,
	Alex Shi <alex.shu@...el.com>,
	Jan Beulich <jbeulich@...ell.com>,
	Robert Richter <robert.richter@....com>,
	Andy Lutomirski <luto@...capital.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Hugh Dickins <hughd@...gle.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Mel Gorman <mgorman@...e.de>, linux-kernel@...r.kernel.org
Subject: [PATCH, RFC 5/6] mm: make clear_huge_page cache clear only around the fault address

From: Andi Kleen <ak@...ux.intel.com>

Clearing a 2MB huge page will typically blow away several levels
of CPU caches. To avoid this only cache clear the 4K area
around the fault address and use a cache avoiding clears
for the rest of the 2MB area.

TBD add numbers

Signed-off-by: Andi Kleen <ak@...ux.intel.com>
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
---
 mm/memory.c |   30 +++++++++++++++++++++++++++---
 1 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index c356ead..b4740cf 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3957,18 +3957,35 @@ EXPORT_SYMBOL(might_fault);
 #endif
 
 #if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_HUGETLBFS)
+
+#ifndef ARCH_HAS_USER_NOCACHE
+#define ARCH_HAS_USER_NOCACHE 0
+#endif
+
+#if ARCH_HAS_USER_NOCACHE == 0
+#define clear_user_highpage_nocache clear_user_highpage
+#endif
+
 static void clear_gigantic_page(struct page *page,
 				unsigned long addr,
 				unsigned int pages_per_huge_page)
 {
 	int i;
 	struct page *p = page;
+	unsigned long vaddr;
+	unsigned long haddr = addr & HPAGE_PMD_MASK;
+	int target = (addr - haddr) >> PAGE_SHIFT;
 
 	might_sleep();
+	vaddr = haddr;
 	for (i = 0; i < pages_per_huge_page;
 	     i++, p = mem_map_next(p, page, i)) {
 		cond_resched();
-		clear_user_highpage(p, addr + i * PAGE_SIZE);
+		vaddr = haddr + i*PAGE_SIZE;
+		if (!ARCH_HAS_USER_NOCACHE  || i == target)
+			clear_user_highpage(p, vaddr);
+		else
+			clear_user_highpage_nocache(p, vaddr);
 	}
 }
 void clear_huge_page(struct page *page,
@@ -3976,16 +3993,23 @@ void clear_huge_page(struct page *page,
 {
 	int i;
 	unsigned long haddr = addr & HPAGE_PMD_MASK;
+	unsigned long vaddr;
+	int target = (addr - haddr) >> PAGE_SHIFT;
 
 	if (unlikely(pages_per_huge_page > MAX_ORDER_NR_PAGES)) {
-		clear_gigantic_page(page, haddr, pages_per_huge_page);
+		clear_gigantic_page(page, addr, pages_per_huge_page);
 		return;
 	}
 
 	might_sleep();
+	vaddr = haddr;
 	for (i = 0; i < pages_per_huge_page; i++) {
 		cond_resched();
-		clear_user_highpage(page + i, haddr + i * PAGE_SIZE);
+		vaddr = haddr + i*PAGE_SIZE;
+		if (!ARCH_HAS_USER_NOCACHE || i == target)
+			clear_user_highpage(page + i, vaddr);
+		else
+			clear_user_highpage_nocache(page + i, vaddr);
 	}
 }
 
-- 
1.7.7.6

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