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Subject: Re: [PATCH 1/2] slab: __GFP_ZERO is incompatible with a constructor
To:     Matthew Wilcox <willy@infradead.org>, linux-mm@kvack.org
Cc:     Matthew Wilcox <mawilcox@microsoft.com>,
        Christoph Lameter <cl@linux.com>,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org, Jan Kara <jack@suse.cz>,
        Jeff Layton <jlayton@redhat.com>,
        Mel Gorman <mgorman@techsingularity.net>,
        stable@vger.kernel.org
References: <20180410125351.15837-1-willy@infradead.org>
From:   Eric Dumazet <eric.dumazet@gmail.com>
Message-ID: <fee8a8bc-3db5-a66a-33cb-0729143ba615@gmail.com>
Date:   Tue, 10 Apr 2018 06:53:04 -0700
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On 04/10/2018 05:53 AM, Matthew Wilcox wrote:
> From: Matthew Wilcox <mawilcox@microsoft.com>
> 
> __GFP_ZERO requests that the object be initialised to all-zeroes,
> while the purpose of a constructor is to initialise an object to a
> particular pattern.  We cannot do both.  Add a warning to catch any
> users who mistakenly pass a __GFP_ZERO flag when allocating a slab with
> a constructor.
> 
> Fixes: d07dbea46405 ("Slab allocators: support __GFP_ZERO in all allocators")
> Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
> Cc: stable@vger.kernel.org


Since there are probably no bug to fix, what about adding the extra check
only for some DEBUG option ?

How many caches are still using ctor these days ?