linux-kernel - Re: + thp-extract-khugepaged-from-mm-huge

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Date:	Thu, 9 Jun 2016 01:57:55 +0300
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	linux-kernel@...r.kernel.org
Cc:	akpm@...ux-foundation.org, aarcange@...hat.com,
	andreslc@...gle.com, aneesh.kumar@...ux.vnet.ibm.com,
	cl@...two.org, dave.hansen@...el.com, hughd@...gle.com,
	jmarchan@...hat.com, kirill.shutemov@...ux.intel.com,
	n-horiguchi@...jp.nec.com, neha.agbk@...il.com,
	peterz@...radead.org, quning@...il.com, sasha.levin@...cle.com,
	vbabka@...e.cz, yang.shi@...aro.org, mm-commits@...r.kernel.org
Subject: Re: + thp-extract-khugepaged-from-mm-huge_memoryc-fix.patch added to
 -mm tree

On Wed, Jun 08, 2016 at 02:55:01PM -0700, akpm@...ux-foundation.org wrote:
> 
> The patch titled
>      Subject: thp-extract-khugepaged-from-mm-huge_memoryc-fix
> has been added to the -mm tree.  Its filename is
>      thp-extract-khugepaged-from-mm-huge_memoryc-fix.patch
> 
> This patch should soon appear at
>     http://ozlabs.org/~akpm/mmots/broken-out/thp-extract-khugepaged-from-mm-huge_memoryc-fix.patch
> and later at
>     http://ozlabs.org/~akpm/mmotm/broken-out/thp-extract-khugepaged-from-mm-huge_memoryc-fix.patch
> 
> Before you just go and hit "reply", please:
>    a) Consider who else should be cc'ed
>    b) Prefer to cc a suitable mailing list as well
>    c) Ideally: find the original patch on the mailing list and do a
>       reply-to-all to that, adding suitable additional cc's
> 
> *** Remember to use Documentation/SubmitChecklist when testing your code ***
> 
> The -mm tree is included into linux-next and is updated
> there every 3-4 working days
> 
> ------------------------------------------------------
> From: Andrew Morton <akpm@...ux-foundation.org>
> Subject: thp-extract-khugepaged-from-mm-huge_memoryc-fix
> 
> khugepaged_mutex can be static to mm/huge_memory.c:enabled_store()
> 
> Makes me wonder what it actually does...

IIUC, it protects khugepaged_thread.

What about something like this:

diff --git a/include/linux/khugepaged.h b/include/linux/khugepaged.h
index f7b4b7dc97bc..1e032a1ddb3e 100644
--- a/include/linux/khugepaged.h
+++ b/include/linux/khugepaged.h
@@ -4,7 +4,6 @@
 #include <linux/sched.h> /* MMF_VM_HUGEPAGE */
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
-extern struct mutex khugepaged_mutex;
 extern struct attribute_group khugepaged_attr_group;
 
 extern int khugepaged_init(void);
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index eaf3a4a655a6..522cf178f118 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -181,12 +181,7 @@ static ssize_t enabled_store(struct kobject *kobj,
 				TRANSPARENT_HUGEPAGE_REQ_MADV_FLAG);
 
 	if (ret > 0) {
-		int err;
-
-		mutex_lock(&khugepaged_mutex);
-		err = start_stop_khugepaged();
-		mutex_unlock(&khugepaged_mutex);
-
+		int err = start_stop_khugepaged();
 		if (err)
 			ret = err;
 	}
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 71a6f9bedfdc..6f5815488c6c 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -58,8 +58,6 @@ static unsigned int khugepaged_scan_sleep_millisecs __read_mostly = 10000;
 /* during fragmentation poll the hugepage allocator once every minute */
 static unsigned int khugepaged_alloc_sleep_millisecs __read_mostly = 60000;
 static unsigned long khugepaged_sleep_expire;
-static struct task_struct *khugepaged_thread __read_mostly;
-DEFINE_MUTEX(khugepaged_mutex);
 static DEFINE_SPINLOCK(khugepaged_mm_lock);
 static DECLARE_WAIT_QUEUE_HEAD(khugepaged_wait);
 /*
@@ -1885,7 +1883,11 @@ static void set_recommended_min_free_kbytes(void)
 
 int start_stop_khugepaged(void)
 {
+	static struct task_struct *khugepaged_thread __read_mostly;
+	static DEFINE_MUTEX(khugepaged_mutex);
 	int err = 0;
+
+	mutex_lock(&khugepaged_mutex);
 	if (khugepaged_enabled()) {
 		if (!khugepaged_thread)
 			khugepaged_thread = kthread_run(khugepaged, NULL,
@@ -1906,5 +1908,6 @@ int start_stop_khugepaged(void)
 		khugepaged_thread = NULL;
 	}
 fail:
+	mutex_unlock(&khugepaged_mutex);
 	return err;
 }
-- 
 Kirill A. Shutemov