linux-kernel - Re: [PATCH 3/3] thp: limit number of object to scan on deferred_split

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Date:	Thu, 4 Feb 2016 15:11:59 +0200
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>
Cc:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Hugh Dickins <hughd@...gle.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Christoph Lameter <cl@...two.org>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Steve Capper <steve.capper@...aro.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>,
	Jerome Marchand <jmarchan@...hat.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 3/3] thp: limit number of object to scan on
 deferred_split_scan()

On Thu, Jan 21, 2016 at 03:09:23PM +0300, Kirill A. Shutemov wrote:
> If we have a lot of pages in queue to be split, deferred_split_scan()
> can spend unreasonable amount of time under spinlock with disabled
> interrupts.
> 
> Let's cap number of pages to split on scan by sc->nr_to_scan.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Reported-by: Andrea Arcangeli <aarcange@...hat.com>
> ---
>  mm/huge_memory.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 36f98459f854..298dbc001b07 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -3478,17 +3478,19 @@ static unsigned long deferred_split_scan(struct shrinker *shrink,
>  	int split = 0;
>  
>  	spin_lock_irqsave(&pgdata->split_queue_lock, flags);
> -	list_splice_init(&pgdata->split_queue, &list);
> -
>  	/* Take pin on all head pages to avoid freeing them under us */
>  	list_for_each_safe(pos, next, &list) {

Well, that's embarrassing... :-/

I forgot to commit one local change here. Sorry.

>From 5b27991afe0e4018f2503593ade85d35ce045fbc Mon Sep 17 00:00:00 2001
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Date: Thu, 4 Feb 2016 15:40:03 +0300
Subject: [PATCH] thp: get deferred_split_scan() work again

We really need to iterate over split_queue, not local empty list to get
anything split from the shrinker.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Fixes: e3ae19535c66 ("thp: limit number of object to scan on deferred_split_scan()")
---
 mm/huge_memory.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 36c070167b71..08fc0ba2207e 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3482,7 +3482,7 @@ static unsigned long deferred_split_scan(struct shrinker *shrink,
 
 	spin_lock_irqsave(&pgdata->split_queue_lock, flags);
 	/* Take pin on all head pages to avoid freeing them under us */
-	list_for_each_safe(pos, next, &list) {
+	list_for_each_safe(pos, next, &pgdata->split_queue) {
 		page = list_entry((void *)pos, struct page, mapping);
 		page = compound_head(page);
 		if (get_page_unless_zero(page)) {
-- 
 Kirill A. Shutemov