linux-kernel - Re: [PATCH 1/2] slab: __GFP_ZERO is incompatible with a constructor

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Date:   Tue, 10 Apr 2018 06:53:04 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Matthew Wilcox <willy@...radead.org>, linux-mm@...ck.org
Cc:     Matthew Wilcox <mawilcox@...rosoft.com>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, Jan Kara <jack@...e.cz>,
        Jeff Layton <jlayton@...hat.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        stable@...r.kernel.org
Subject: Re: [PATCH 1/2] slab: __GFP_ZERO is incompatible with a constructor



On 04/10/2018 05:53 AM, Matthew Wilcox wrote:
> From: Matthew Wilcox <mawilcox@...rosoft.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@...rosoft.com>
> Cc: stable@...r.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 ?