linux-kernel - [PATCHv3, RFC 03/34] mm: implement zero_huge_user

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Message-Id: <1365163198-29726-4-git-send-email-kirill.shutemov@linux.intel.com>
Date:	Fri,  5 Apr 2013 14:59:27 +0300
From:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:	Andrea Arcangeli <aarcange@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Al Viro <viro@...iv.linux.org.uk>, Hugh Dickins <hughd@...gle.com>,
	Wu Fengguang <fengguang.wu@...el.com>, Jan Kara <jack@...e.cz>,
	Mel Gorman <mgorman@...e.de>, linux-mm@...ck.org,
	Andi Kleen <ak@...ux.intel.com>,
	Matthew Wilcox <matthew.r.wilcox@...el.com>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Hillf Danton <dhillf@...il.com>, Dave Hansen <dave@...1.net>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: [PATCHv3, RFC 03/34] mm: implement zero_huge_user_segment and friends

From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>

Let's add helpers to clear huge page segment(s). They provide the same
functionallity as zero_user_segment and zero_user, but for huge pages.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
---
 include/linux/mm.h |    7 +++++++
 mm/memory.c        |   36 ++++++++++++++++++++++++++++++++++++
 2 files changed, 43 insertions(+)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 5b7fd4e..09530c7 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1731,6 +1731,13 @@ extern void dump_page(struct page *page);
 extern void clear_huge_page(struct page *page,
 			    unsigned long addr,
 			    unsigned int pages_per_huge_page);
+extern void zero_huge_user_segment(struct page *page,
+		unsigned start, unsigned end);
+static inline void zero_huge_user(struct page *page,
+		unsigned start, unsigned len)
+{
+	zero_huge_user_segment(page, start, start + len);
+}
 extern void copy_user_huge_page(struct page *dst, struct page *src,
 				unsigned long addr, struct vm_area_struct *vma,
 				unsigned int pages_per_huge_page);
diff --git a/mm/memory.c b/mm/memory.c
index 494526a..9da540f 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4213,6 +4213,42 @@ void clear_huge_page(struct page *page,
 	}
 }
 
+void zero_huge_user_segment(struct page *page, unsigned start, unsigned end)
+{
+	int i;
+	unsigned start_idx, end_idx;
+	unsigned start_off, end_off;
+
+	BUG_ON(end < start);
+
+	might_sleep();
+
+	if (start == end)
+		return;
+
+	start_idx = start >> PAGE_SHIFT;
+	start_off = start & ~PAGE_MASK;
+	end_idx = (end - 1) >> PAGE_SHIFT;
+	end_off = ((end - 1) & ~PAGE_MASK) + 1;
+
+	/*
+	 * if start and end are on the same small page we can call
+	 * zero_user_segment() once and save one kmap_atomic().
+	 */
+	if (start_idx == end_idx)
+		return zero_user_segment(page + start_idx, start_off, end_off);
+
+	/* zero the first (possibly partial) page */
+	zero_user_segment(page + start_idx, start_off, PAGE_SIZE);
+	for (i = start_idx + 1; i < end_idx; i++) {
+		cond_resched();
+		clear_highpage(page + i);
+		flush_dcache_page(page + i);
+	}
+	/* zero the last (possibly partial) page */
+	zero_user_segment(page + end_idx, 0, end_off);
+}
+
 static void copy_user_gigantic_page(struct page *dst, struct page *src,
 				    unsigned long addr,
 				    struct vm_area_struct *vma,
-- 
1.7.10.4

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