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From: David Rientjes <rientjes@google.com>
To: Christopher Lameter <cl@linux.com>
Cc: Vlastimil Babka <vbabka@suse.cz>,
	linux-mm@kvack.org, Pekka Enberg <penberg@kernel.org>,
	Joonsoo Kim <iamjoonsoo.kim@lge.com>,
	Ming Lei <ming.lei@redhat.com>,
	Dave Chinner <david@fromorbit.com>,
	Matthew Wilcox <willy@infradead.org>,
	"Darrick J . Wong" <darrick.wong@oracle.com>,
	Christoph Hellwig <hch@lst.de>, Michal Hocko <mhocko@kernel.org>,
	linux-kernel@vger.kernel.org, linux-xfs@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org
Subject: Re: [RFC 0/2] guarantee natural alignment for kmalloc()
Date: Tue, 19 Mar 2019 17:53:51 -0700 (PDT)	[thread overview]
Message-ID: <alpine.DEB.2.21.1903191751560.18028@chino.kir.corp.google.com> (raw)
In-Reply-To: <01000169988d4e34-b4178f68-c390-472b-b62f-a57a4f459a76-000000@email.amazonses.com>

On Wed, 20 Mar 2019, Christopher Lameter wrote:

> > The recent thread [1] inspired me to look into guaranteeing alignment for
> > kmalloc() for power-of-two sizes. Turns out it's not difficult and in most
> > configuration nothing really changes as it happens implicitly. More details in
> > the first patch. If we agree we want to do this, I will see where to update
> > documentation and perhaps if there are any workarounds in the tree that can be
> > converted to plain kmalloc() afterwards.
> 
> This means that the alignments are no longer uniform for all kmalloc
> caches and we get back to code making all sorts of assumptions about
> kmalloc alignments.
> 
> Currently all kmalloc objects are aligned to KMALLOC_MIN_ALIGN. That will
> no longer be the case and alignments will become inconsistent.
> 
> I think its valuable that alignment requirements need to be explicitly
> requested.
> 
> Lets add an array of power of two aligned kmalloc caches if that is really
> necessary. Add some GFP_XXX flag to kmalloc to make it ^2 aligned maybe?
> 

No objection, but I think the GFP flags should remain what they are for: 
to Get Free Pages.  If we are to add additional flags to specify 
characteristics of slab objects, can we add a kmalloc_flags() variant that 
will take a new set of flags?  SLAB_OBJ_ALIGN_POW2?

  reply	other threads:[~2019-03-20  0:53 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-03-19 21:11 [RFC 0/2] guarantee natural alignment for kmalloc() Vlastimil Babka
2019-03-19 21:11 ` [RFC 1/2] mm, sl[aou]b: guarantee natural alignment for kmalloc(power-of-two) Vlastimil Babka
2019-03-19 21:11 ` [RFC 2/2] mm, sl[aou]b: test whether kmalloc() alignment works as expected Vlastimil Babka
2019-03-20  0:44   ` Christopher Lameter
2019-03-20  0:43 ` [RFC 0/2] guarantee natural alignment for kmalloc() Christopher Lameter
2019-03-20  0:53   ` David Rientjes [this message]
2019-03-20  8:48   ` Vlastimil Babka
2019-03-20 18:20     ` Christopher Lameter
2019-03-21  7:42       ` Vlastimil Babka
2019-03-22 17:52         ` Christopher Lameter
2019-04-05 17:11           ` Vlastimil Babka
2019-04-07  8:00             ` Christoph Hellwig
2019-04-09  8:07               ` Vlastimil Babka
2019-04-09  9:20                 ` Michal Hocko
2019-03-20 18:53     ` Matthew Wilcox
2019-03-20 21:48       ` Vlastimil Babka
2019-03-21  2:23         ` Matthew Wilcox
2019-03-21  7:02           ` Vlastimil Babka

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