linux-kernel - Re: [PATCH] thp: reduce khugepaged freezing latency

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Message-ID: <20111109194047.GO5075@redhat.com>
Date:	Wed, 9 Nov 2011 20:40:48 +0100
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	"Rafael J. Wysocki" <rjw@...e.com>, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, Jiri Slaby <jirislaby@...il.com>,
	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] thp: reduce khugepaged freezing latency

On Wed, Nov 09, 2011 at 10:34:47AM -0800, Tejun Heo wrote:
> know.  My instinct tells me to strongly recommend use of
> wait_event_freezable_timeout() and run away.  :)

Passing false wasn't so appealing to me but ok. Jiri can you test this
with some suspend? (beware builds but untested)

===
From: Andrea Arcangeli <aarcange@...hat.com>
Subject: thp: reduce khugepaged freezing latency

Use wait_event_freezable_timeout() instead of
schedule_timeout_interruptible() to avoid missing freezer wakeups. A
try_to_freeze() would have been needed in the
khugepaged_alloc_hugepage tight loop too in case of the allocation
failing repeatedly, and wait_event_freezable_timeout will provide it
too.

khugepaged would still freeze just fine by trying again the next
minute but it's better if it freezes immediately.

Reported-by: Jiri Slaby <jslaby@...e.cz>
Signed-off-by: Andrea Arcangeli <aarcange@...hat.com>
---
 mm/huge_memory.c |   14 ++++----------
 1 files changed, 4 insertions(+), 10 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 4298aba..fd925d0 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2259,12 +2259,9 @@ static void khugepaged_do_scan(struct page **hpage)
 
 static void khugepaged_alloc_sleep(void)
 {
-	DEFINE_WAIT(wait);
-	add_wait_queue(&khugepaged_wait, &wait);
-	schedule_timeout_interruptible(
-		msecs_to_jiffies(
-			khugepaged_alloc_sleep_millisecs));
-	remove_wait_queue(&khugepaged_wait, &wait);
+	wait_event_freezable_timeout(khugepaged_wait, false,
+				     msecs_to_jiffies(
+					     khugepaged_alloc_sleep_millisecs));
 }
 
 #ifndef CONFIG_NUMA
@@ -2313,14 +2310,11 @@ static void khugepaged_loop(void)
 		if (unlikely(kthread_should_stop()))
 			break;
 		if (khugepaged_has_work()) {
-			DEFINE_WAIT(wait);
 			if (!khugepaged_scan_sleep_millisecs)
 				continue;
-			add_wait_queue(&khugepaged_wait, &wait);
-			schedule_timeout_interruptible(
+			wait_event_freezable_timeout(khugepaged_wait, false,
 				msecs_to_jiffies(
 					khugepaged_scan_sleep_millisecs));
-			remove_wait_queue(&khugepaged_wait, &wait);
 		} else if (khugepaged_enabled())
 			wait_event_freezable(khugepaged_wait,
 					     khugepaged_wait_event());
--
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