linux-kernel - [PATCH 4/5] teach smaps_pte

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Date:	Mon, 21 Feb 2011 17:53:43 -0800
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	linux-mm@...ck.org, Michael J Wolf <mjwolf@...ibm.com>,
	Andrea Arcangeli <aarcange@...hat.com>, akpm@...l.org,
	Dave Hansen <dave@...ux.vnet.ibm.com>,
	Mel Gorman <mel@....ul.ie>,
	Johannes Weiner <hannes@...xchg.org>
Subject: [PATCH 4/5] teach smaps_pte_range() about THP pmds


v2 - used mm->page_table_lock to fix up locking bug that
	Mel pointed out.  Also remove Acks since things
	got changed significantly.

This adds code to explicitly detect  and handle
pmd_trans_huge() pmds.  It then passes HPAGE_SIZE units
in to the smap_pte_entry() function instead of PAGE_SIZE.

This means that using /proc/$pid/smaps now will no longer
cause THPs to be broken down in to small pages.

Signed-off-by: Dave Hansen <dave@...ux.vnet.ibm.com>
---

 linux-2.6.git-dave/fs/proc/task_mmu.c |   23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

diff -puN fs/proc/task_mmu.c~teach-smaps_pte_range-about-thp-pmds fs/proc/task_mmu.c
--- linux-2.6.git/fs/proc/task_mmu.c~teach-smaps_pte_range-about-thp-pmds	2011-02-14 09:59:44.034590716 -0800
+++ linux-2.6.git-dave/fs/proc/task_mmu.c	2011-02-21 15:12:46.144181298 -0800
@@ -1,5 +1,6 @@
 #include <linux/mm.h>
 #include <linux/hugetlb.h>
+#include <linux/huge_mm.h>
 #include <linux/mount.h>
 #include <linux/seq_file.h>
 #include <linux/highmem.h>
@@ -7,6 +8,7 @@
 #include <linux/slab.h>
 #include <linux/pagemap.h>
 #include <linux/mempolicy.h>
+#include <linux/rmap.h>
 #include <linux/swap.h>
 #include <linux/swapops.h>
 
@@ -385,8 +387,25 @@ static int smaps_pte_range(pmd_t *pmd, u
 	pte_t *pte;
 	spinlock_t *ptl;
 
-	split_huge_page_pmd(walk->mm, pmd);
-
+	spin_lock(&walk->mm->page_table_lock);
+	if (pmd_trans_huge(*pmd)) {
+		if (pmd_trans_splitting(*pmd)) {
+			spin_unlock(&walk->mm->page_table_lock);
+			wait_split_huge_page(vma->anon_vma, pmd);
+		} else {
+			smaps_pte_entry(*(pte_t *)pmd, addr,
+					HPAGE_PMD_SIZE, walk);
+			spin_unlock(&walk->mm->page_table_lock);
+			return 0;
+		}
+	} else {
+		spin_unlock(&walk->mm->page_table_lock);
+	}
+	/*
+	 * The mmap_sem held all the way back in m_start() is what
+	 * keeps khugepaged out of here and from collapsing things
+	 * in here.
+	 */
 	pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
 	for (; addr != end; pte++, addr += PAGE_SIZE)
 		smaps_pte_entry(*pte, addr, PAGE_SIZE, walk);
diff -puN mm/migrate.c~teach-smaps_pte_range-about-thp-pmds mm/migrate.c
diff -puN mm/mincore.c~teach-smaps_pte_range-about-thp-pmds mm/mincore.c
diff -puN include/linux/mm.h~teach-smaps_pte_range-about-thp-pmds include/linux/mm.h
diff -puN mm/mempolicy.c~teach-smaps_pte_range-about-thp-pmds mm/mempolicy.c
_
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