Re: [PATCH v3 RFC 14/14] mm: speedup page alloc for MPOL_PREFERRED_MANY by adding a NO_SLOWPATH gfp bit

From: Michal Hocko <mhocko@suse.com>
To: Feng Tang <feng.tang@intel.com>
Cc: Dave Hansen <dave.hansen@intel.com>,
	Ben Widawsky <ben.widawsky@intel.com>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Andrea Arcangeli <aarcange@redhat.com>,
	David Rientjes <rientjes@google.com>,
	Mel Gorman <mgorman@techsingularity.net>,
	Mike Kravetz <mike.kravetz@oracle.com>,
	Randy Dunlap <rdunlap@infradead.org>,
	Vlastimil Babka <vbabka@suse.cz>, Andi Kleen <ak@linux.intel.com>,
	"Williams, Dan J" <dan.j.williams@intel.com>
Subject: Re: [PATCH v3 RFC 14/14] mm: speedup page alloc for MPOL_PREFERRED_MANY by adding a NO_SLOWPATH gfp bit
Date: Wed, 10 Mar 2021 10:44:11 +0100	[thread overview]
Message-ID: <YEiU6/5BXM7v4AOu@dhcp22.suse.cz> (raw)
In-Reply-To: <20210310051947.GA33036@shbuild999.sh.intel.com>

On Wed 10-03-21 13:19:47, Feng Tang wrote:
[...]
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index d66c1c0..00b19f7 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -2205,9 +2205,13 @@ static struct page *alloc_pages_policy(struct mempolicy *pol, gfp_t gfp,
>  	 * | MPOL_PREFERRED_MANY (round 2) | local         | NULL       |
>  	 * +-------------------------------+---------------+------------+
>  	 */
> -	if (pol->mode == MPOL_PREFERRED_MANY)
> +	if (pol->mode == MPOL_PREFERRED_MANY) {
>  		gfp_mask |= __GFP_RETRY_MAYFAIL | __GFP_NOWARN;
>  
> +		/* Skip direct reclaim, as there will be a second try */
> +		gfp_mask &= ~__GFP_DIRECT_RECLAIM;

__GFP_RETRY_MAYFAIL is a reclaim modifier which doesn't make any sense
without __GFP_DIRECT_RECLAIM. Also I think it would be better to have a
proper allocation flags in the initial patch which implements the
fallback.

> +	}
> +
>  	page = __alloc_pages_nodemask(gfp_mask, order,
>  				      policy_node(gfp, pol, preferred_nid),
>  				      policy_nodemask(gfp, pol));
> -- 
> 2.7.4
> 
> 

-- 
Michal Hocko
SUSE Labs