linux-kernel - Re: [RFC 0/2] guarantee natural alignment for kmalloc()

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Message-ID: <20190320185347.GZ19508@bombadil.infradead.org>
Date:   Wed, 20 Mar 2019 11:53:47 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Christopher Lameter <cl@...ux.com>, linux-mm@...ck.org,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Ming Lei <ming.lei@...hat.com>,
        Dave Chinner <david@...morbit.com>,
        "Darrick J . Wong" <darrick.wong@...cle.com>,
        Christoph Hellwig <hch@....de>,
        Michal Hocko <mhocko@...nel.org>, linux-kernel@...r.kernel.org,
        linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-block@...r.kernel.org
Subject: Re: [RFC 0/2] guarantee natural alignment for kmalloc()

On Wed, Mar 20, 2019 at 09:48:47AM +0100, Vlastimil Babka wrote:
> Natural alignment to size is rather well defined, no? Would anyone ever
> assume a larger one, for what reason?
> It's now where some make assumptions (even unknowingly) for natural
> There are two 'odd' sizes 96 and 192, which will keep cacheline size
> alignment, would anyone really expect more than 64 bytes?

Presumably 96 will keep being aligned to 32 bytes, as aligning 96 to 64
just results in 128-byte allocations.