Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1752198AbbLCQqN (ORCPT <rfc822;w@1wt.eu>);
	Thu, 3 Dec 2015 11:46:13 -0500
Received: from mail-wm0-f50.google.com ([74.125.82.50]:35262 "EHLO
	mail-wm0-f50.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1751416AbbLCQqM (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Thu, 3 Dec 2015 11:46:12 -0500
Date: Thu, 3 Dec 2015 17:46:09 +0100
From: Michal Hocko <mhocko@kernel.org>
To: Johannes Weiner <hannes@cmpxchg.org>
Cc: Andrew Morton <akpm@linux-foundation.org>, Rik van Riel <riel@redhat.com>,
        Mel Gorman <mgorman@suse.de>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] proc: meminfo: estimate available memory more
 conservatively
Message-ID: <20151203164609.GC9271@dhcp22.suse.cz>
References: <1448913622-24198-1-git-send-email-hannes@cmpxchg.org>
 <1448913622-24198-2-git-send-email-hannes@cmpxchg.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <1448913622-24198-2-git-send-email-hannes@cmpxchg.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
Content-Length: 2071
Lines: 59

On Mon 30-11-15 15:00:22, Johannes Weiner wrote:
> The MemAvailable item in /proc/meminfo is to give users a hint of how
> much memory is allocatable without causing swapping, so it excludes
> the zones' low watermarks as unavailable to userspace.
> 
> However, for a userspace allocation, kswapd will actually reclaim
> until the free pages hit a combination of the high watermark and the
> page allocator's lowmem protection that keeps a certain amount of DMA
> and DMA32 memory from userspace as well.
> 
> Subtract the full amount we know to be unavailable to userspace from
> the number of free pages when calculating MemAvailable.

I am not sure this will make a big or even noticeable difference in the
real life but it makes sense.

> 
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>

Acked-by: Michal Hocko <mhocko@suse.com>

> ---
>  fs/proc/meminfo.c | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
> 
> diff --git a/fs/proc/meminfo.c b/fs/proc/meminfo.c
> index 9155a5a..df4661a 100644
> --- a/fs/proc/meminfo.c
> +++ b/fs/proc/meminfo.c
> @@ -57,11 +57,8 @@ static int meminfo_proc_show(struct seq_file *m, void *v)
>  	/*
>  	 * Estimate the amount of memory available for userspace allocations,
>  	 * without causing swapping.
> -	 *
> -	 * Free memory cannot be taken below the low watermark, before the
> -	 * system starts swapping.
>  	 */
> -	available = i.freeram - wmark_low;
> +	available = i.freeram - totalreserve_pages;
>  
>  	/*
>  	 * Not all the page cache can be freed, otherwise the system will
> -- 
> 2.6.2
> 
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org.  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>

-- 
Michal Hocko
SUSE Labs
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/