linux-kernel - Re: [PATCH v3 07/13] mm, compaction: skip rechecks when lock was already held

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20140624185534.GA11945@nhori.redhat.com>
Date:	Tue, 24 Jun 2014 14:55:34 -0400
From:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:	Vlastimil Babka <vbabka@...e.cz>
Cc:	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	David Rientjes <rientjes@...gle.com>,
	Minchan Kim <minchan@...nel.org>, Mel Gorman <mgorman@...e.de>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Michal Nazarewicz <mina86@...a86.com>,
	Christoph Lameter <cl@...ux.com>,
	Rik van Riel <riel@...hat.com>,
	Zhang Yanfei <zhangyanfei@...fujitsu.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 07/13] mm, compaction: skip rechecks when lock was
 already held

On Fri, Jun 20, 2014 at 05:49:37PM +0200, Vlastimil Babka wrote:
> Compaction scanners try to lock zone locks as late as possible by checking
> many page or pageblock properties opportunistically without lock and skipping
> them if not unsuitable. For pages that pass the initial checks, some properties
> have to be checked again safely under lock. However, if the lock was already
> held from a previous iteration in the initial checks, the rechecks are
> unnecessary.
> 
> This patch therefore skips the rechecks when the lock was already held. This is
> now possible to do, since we don't (potentially) drop and reacquire the lock
> between the initial checks and the safe rechecks anymore.
> 
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
> Acked-by: Minchan Kim <minchan@...nel.org>
> Cc: Mel Gorman <mgorman@...e.de>
> Cc: Michal Nazarewicz <mina86@...a86.com>
> Cc: Naoya Horiguchi <n-horiguchi@...jp.nec.com>
> Cc: Christoph Lameter <cl@...ux.com>
> Cc: Rik van Riel <riel@...hat.com>
> Acked-by: David Rientjes <rientjes@...gle.com>

Reviewed-by: Naoya Horiguchi <n-horiguchi@...jp.nec.com>

> ---
>  mm/compaction.c | 53 +++++++++++++++++++++++++++++++----------------------
>  1 file changed, 31 insertions(+), 22 deletions(-)
> 
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 40da812..9f6e857 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -324,22 +324,30 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
>  			goto isolate_fail;
>  
>  		/*
> -		 * The zone lock must be held to isolate freepages.
> -		 * Unfortunately this is a very coarse lock and can be
> -		 * heavily contended if there are parallel allocations
> -		 * or parallel compactions. For async compaction do not
> -		 * spin on the lock and we acquire the lock as late as
> -		 * possible.
> +		 * If we already hold the lock, we can skip some rechecking.
> +		 * Note that if we hold the lock now, checked_pageblock was
> +		 * already set in some previous iteration (or strict is true),
> +		 * so it is correct to skip the suitable migration target
> +		 * recheck as well.
>  		 */
> -		if (!locked)
> +		if (!locked) {
> +			/*
> +			 * The zone lock must be held to isolate freepages.
> +			 * Unfortunately this is a very coarse lock and can be
> +			 * heavily contended if there are parallel allocations
> +			 * or parallel compactions. For async compaction do not
> +			 * spin on the lock and we acquire the lock as late as
> +			 * possible.
> +			 */
>  			locked = compact_trylock_irqsave(&cc->zone->lock,
>  								&flags, cc);
> -		if (!locked)
> -			break;
> +			if (!locked)
> +				break;
>  
> -		/* Recheck this is a buddy page under lock */
> -		if (!PageBuddy(page))
> -			goto isolate_fail;
> +			/* Recheck this is a buddy page under lock */
> +			if (!PageBuddy(page))
> +				goto isolate_fail;
> +		}
>  
>  		/* Found a free page, break it into order-0 pages */
>  		isolated = split_free_page(page);
> @@ -623,19 +631,20 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
>  		    page_count(page) > page_mapcount(page))
>  			continue;
>  
> -		/* If the lock is not held, try to take it */
> -		if (!locked)
> +		/* If we already hold the lock, we can skip some rechecking */
> +		if (!locked) {
>  			locked = compact_trylock_irqsave(&zone->lru_lock,
>  								&flags, cc);
> -		if (!locked)
> -			break;
> +			if (!locked)
> +				break;
>  
> -		/* Recheck PageLRU and PageTransHuge under lock */
> -		if (!PageLRU(page))
> -			continue;
> -		if (PageTransHuge(page)) {
> -			low_pfn += (1 << compound_order(page)) - 1;
> -			continue;
> +			/* Recheck PageLRU and PageTransHuge under lock */
> +			if (!PageLRU(page))
> +				continue;
> +			if (PageTransHuge(page)) {
> +				low_pfn += (1 << compound_order(page)) - 1;
> +				continue;
> +			}
>  		}
>  
>  		lruvec = mem_cgroup_page_lruvec(page, zone);
> -- 
> 1.8.4.5
> 
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@...ck.org.  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@...ck.org"> email@...ck.org </a>
> 
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/