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

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Date:   Tue, 10 Apr 2018 09:26:19 -0500 (CDT)
From:   Christopher Lameter <cl@...ux.com>
To:     Matthew Wilcox <willy@...radead.org>
cc:     linux-mm@...ck.org, Matthew Wilcox <mawilcox@...rosoft.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 Tue, 10 Apr 2018, Christopher Lameter wrote:

> On Tue, 10 Apr 2018, Matthew Wilcox wrote:
>
> > __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.
>
> Can we move this check out of the critical paths and check for
> a ctor and GFP_ZERO when calling the page allocator? F.e. in
> allocate_slab()?

The ctor's are run at that point from setup_object() so it makes sense.