From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1752805AbbKLMje (ORCPT <rfc822;w@1wt.eu>);
	Thu, 12 Nov 2015 07:39:34 -0500
Received: from mail-wm0-f45.google.com ([74.125.82.45]:33063 "EHLO
	mail-wm0-f45.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1752056AbbKLMjb (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Thu, 12 Nov 2015 07:39:31 -0500
Date: Thu, 12 Nov 2015 13:39:28 +0100
From: Michal Hocko <mhocko@kernel.org>
To: linux-mm@kvack.org
Cc: Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Mel Gorman <mgorman@suse.de>, Johannes Weiner <hannes@cmpxchg.org>,
        Rik van Riel <riel@redhat.com>, David Rientjes <rientjes@google.com>,
        Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RFC 1/3] mm, oom: refactor oom detection
Message-ID: <20151112123928.GH1174@dhcp22.suse.cz>
References: <1446131835-3263-1-git-send-email-mhocko@kernel.org>
 <1446131835-3263-2-git-send-email-mhocko@kernel.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <1446131835-3263-2-git-send-email-mhocko@kernel.org>
User-Agent: Mutt/1.5.24 (2015-08-30)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Thu 29-10-15 16:17:13, mhocko@kernel.org wrote:
[...]
> @@ -3135,13 +3145,56 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order,
>  	if (gfp_mask & __GFP_NORETRY)
>  		goto noretry;
>  
> -	/* Keep reclaiming pages as long as there is reasonable progress */
> +	/*
> +	 * Do not retry high order allocations unless they are __GFP_REPEAT
> +	 * and even then do not retry endlessly.
> +	 */
>  	pages_reclaimed += did_some_progress;
> -	if ((did_some_progress && order <= PAGE_ALLOC_COSTLY_ORDER) ||
> -	    ((gfp_mask & __GFP_REPEAT) && pages_reclaimed < (1 << order))) {
> -		/* Wait for some write requests to complete then retry */
> -		wait_iff_congested(ac->preferred_zone, BLK_RW_ASYNC, HZ/50);
> -		goto retry;
> +	if (order > PAGE_ALLOC_COSTLY_ORDER) {
> +		if (!(gfp_mask & __GFP_REPEAT) || pages_reclaimed >= (1<<order))
> +			goto noretry;

This is not correct because we could fail __GFP_NOFAIL allocation. It
should do
		if (!(gfp_mask & __GFP_NOFAIL) &&
		   (!(gfp_mask & __GFP_REPEAT) || pages_reclaimed >= (1<<order)))
			goto noretry;

It looks rather ugly but it will get much better with patch3 which
reorganizes the code a bit

> +
> +		if (did_some_progress)
> +			goto retry;
> +	}

-- 
Michal Hocko
SUSE Labs