linux-kernel - Re: [PATCH] mm: clarify COMPACTION Kconfig text

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Message-ID: <20160823083830.GC15849@x4>
Date:   Tue, 23 Aug 2016 10:38:30 +0200
From:   Markus Trippelsdorf <markus@...ppelsdorf.de>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...e.de>, Joonsoo Kim <js1304@...il.com>,
        Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>,
        Michal Hocko <mhocko@...e.com>
Subject: Re: [PATCH] mm: clarify COMPACTION Kconfig text

On 2016.08.23 at 10:09 +0200, Michal Hocko wrote:
> From: Michal Hocko <mhocko@...e.com>
> 
> The current wording of the COMPACTION Kconfig help text doesn't
> emphasise that disabling COMPACTION might cripple the page allocator
> which relies on the compaction quite heavily for high order requests and
> an unexpected OOM can happen with the lack of compaction. Make sure
> we are vocal about that.

Just a few nitpicks inline below:

>  mm/Kconfig | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 78a23c5c302d..0dff2f05b6d1 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -262,7 +262,14 @@ config COMPACTION
>  	select MIGRATION
>  	depends on MMU
>  	help
> -	  Allows the compaction of memory for the allocation of huge pages.
> +          Compaction is the only memory management component to form
> +          high order (larger physically contiguous) memory blocks
> +          reliably. Page allocator relies on the compaction heavily and
                       The page allo...      on compaction    
> +          the lack of the feature can lead to unexpected OOM killer
> +          invocation for high order memory requests. You shouldnm't
             invocations                                    shouldn't  
> +          disable this option unless there is really a strong reason for
                                              really is      
> +          it and then we are really interested to hear about that at
                            would be    

-- 
Markus