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

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Date:   Tue, 9 Apr 2019 11:20:42 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Christoph Hellwig <hch@....de>, 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>,
        Matthew Wilcox <willy@...radead.org>,
        "Darrick J . Wong" <darrick.wong@...cle.com>,
        linux-kernel@...r.kernel.org, linux-xfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-block@...r.kernel.org,
        lsf-pc@...ts.linux-foundation.org
Subject: Re: [RFC 0/2] guarantee natural alignment for kmalloc()

On Tue 09-04-19 10:07:42, Vlastimil Babka wrote:
> On 4/7/19 10:00 AM, Christoph Hellwig wrote:
> > On Fri, Apr 05, 2019 at 07:11:17PM +0200, Vlastimil Babka wrote:
> >> On 3/22/19 6:52 PM, Christopher Lameter wrote:
> >> > On Thu, 21 Mar 2019, Vlastimil Babka wrote:
> >> > 
> >> >> That however doesn't work well for the xfs/IO case where block sizes are
> >> >> not known in advance:
> >> >>
> >> >> https://lore.kernel.org/linux-fsdevel/20190225040904.5557-1-ming.lei@redhat.com/T/#ec3a292c358d05a6b29cc4a9ce3ae6b2faf31a23f
> >> > 
> >> > I thought we agreed to use custom slab caches for that?
> >> 
> >> Hm maybe I missed something but my impression was that xfs/IO folks would have
> >> to create lots of them for various sizes not known in advance, and that it
> >> wasn't practical and would welcome if kmalloc just guaranteed the alignment.
> >> But so far they haven't chimed in here in this thread, so I guess I'm wrong.
> > 
> > Yes, in XFS we might have quite a few.  Never mind all the other
> > block level consumers that might have similar reasonable expectations
> > but haven't triggered the problematic drivers yet.
> 
> What about a LSF session/BoF to sort this out, then? Would need to have people
> from all three MM+FS+IO groups, I suppose.

Sounds like a good plan. Care to send an email to lsf-pc mailing list so
that it doesn't fall through cracks please?

-- 
Michal Hocko
SUSE Labs