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[3.8.y.z,extended,stable] Patch "mm: Wait for THP migrations to complete during NUMA hinting faults" has been added to staging queue

Message ID 1383876501-32722-1-git-send-email-kamal@canonical.com
State New
Headers show

Commit Message

Kamal Mostafa Nov. 8, 2013, 2:08 a.m. UTC 
This is a note to let you know that I have just added a patch titled

    mm: Wait for THP migrations to complete during NUMA hinting faults

to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue

This patch is scheduled to be released in version 3.8.13.13.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

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From 7d9e0ed099ab69726fefdcf00835d9c3dbac5747 Mon Sep 17 00:00:00 2001
From: Mel Gorman <mgorman@suse.de>
Date: Mon, 7 Oct 2013 11:28:43 +0100
Subject: mm: Wait for THP migrations to complete during NUMA hinting faults

commit 42836f5f8baa33085f547098b74aa98991ee9216 upstream.

The locking for migrating THP is unusual. While normal page migration
prevents parallel accesses using a migration PTE, THP migration relies on
a combination of the page_table_lock, the page lock and the existance of
the NUMA hinting PTE to guarantee safety but there is a bug in the scheme.

If a THP page is currently being migrated and another thread traps a
fault on the same page it checks if the page is misplaced. If it is not,
then pmd_numa is cleared. The problem is that it checks if the page is
misplaced without holding the page lock meaning that the racing thread
can be migrating the THP when the second thread clears the NUMA bit
and faults a stale page.

This patch checks if the page is potentially being migrated and stalls
using the lock_page if it is potentially being migrated before checking
if the page is misplaced or not.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Reviewed-by: Rik van Riel <riel@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1381141781-10992-6-git-send-email-mgorman@suse.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
 mm/huge_memory.c | 23 ++++++++++++++++-------
 1 file changed, 16 insertions(+), 7 deletions(-)

--
1.8.1.2
diff mbox

Patch

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index a057a7d..f3868de 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1315,13 +1315,14 @@  int do_huge_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
 	if (current_nid == numa_node_id())
 		count_vm_numa_event(NUMA_HINT_FAULTS_LOCAL);

-	target_nid = mpol_misplaced(page, vma, haddr);
-	if (target_nid == -1) {
-		put_page(page);
-		goto clear_pmdnuma;
-	}
+	/*
+	 * Acquire the page lock to serialise THP migrations but avoid dropping
+	 * page_table_lock if at all possible
+	 */
+	if (trylock_page(page))
+		goto got_lock;

-	/* Acquire the page lock to serialise THP migrations */
+	/* Serialise against migrationa and check placement check placement */
 	spin_unlock(&mm->page_table_lock);
 	lock_page(page);
 	page_locked = true;
@@ -1333,9 +1334,17 @@  int do_huge_pmd_numa_page(struct mm_struct *mm, struct vm_area_struct *vma,
 		put_page(page);
 		goto out_unlock;
 	}
-	spin_unlock(&mm->page_table_lock);
+
+got_lock:
+	target_nid = mpol_misplaced(page, vma, haddr);
+	if (target_nid == -1) {
+		unlock_page(page);
+		put_page(page);
+		goto clear_pmdnuma;
+	}

 	/* Migrate the THP to the requested node */
+	spin_unlock(&mm->page_table_lock);
 	migrated = migrate_misplaced_transhuge_page(mm, vma,
 				pmdp, pmd, addr,
 				page, target_nid);