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Date: Tue, 10 Apr 2018 17:03:17 -0500 (CDT)
From: Christopher Lameter <cl@linux.com>
Subject: Re: [PATCH] slub: Remove use of page->counter
In-Reply-To: <20180410205757.GD21336@bombadil.infradead.org>
Message-ID: <alpine.DEB.2.20.1804101702240.30842@nuc-kabylake>
References: <20180410195429.GB21336@bombadil.infradead.org> <alpine.DEB.2.20.1804101545350.30437@nuc-kabylake> <20180410205757.GD21336@bombadil.infradead.org>
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To: Matthew Wilcox <willy@infradead.org>
Cc: linux-mm@kvack.org

On Tue, 10 Apr 2018, Matthew Wilcox wrote:

> > Is this aligned on a doubleword boundary? Maybe move the refcount below
> > the flags field?
>
> You need freelist and _mapcount to be in the same dword.  There's no
> space to put them both in dword 0, so that's used for flags and mapping
> / s_mem.  Then freelist, mapcount and refcount are in dword 1 (on 64-bit),
> or freelist & mapcount are in dword 1 on 32-bit.  After that, 32 and 64-bit
> no longer line up on the same dword boundaries.

Well its no longer clear from the definitions that this must be the case.
Clarify that in the next version?