From: Dave Chinner <david@fromorbit.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: Christopher Lameter <cl@linux.com>,
Vlastimil Babka <vbabka@suse.cz>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Pekka Enberg <penberg@kernel.org>,
David Rientjes <rientjes@google.com>,
Ming Lei <ming.lei@redhat.com>,
"Darrick J . Wong" <darrick.wong@oracle.com>,
Christoph Hellwig <hch@lst.de>,
linux-xfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-block@vger.kernel.org,
James Bottomley <James.Bottomley@hansenpartnership.com>,
linux-btrfs@vger.kernel.org
Subject: Re: [PATCH v2 2/2] mm, sl[aou]b: guarantee natural alignment for kmalloc(power-of-two)
Date: Thu, 29 Aug 2019 08:24:22 +1000 [thread overview]
Message-ID: <20190828222422.GL1119@dread.disaster.area> (raw)
In-Reply-To: <20190828194607.GB6590@bombadil.infradead.org>
On Wed, Aug 28, 2019 at 12:46:08PM -0700, Matthew Wilcox wrote:
> On Wed, Aug 28, 2019 at 06:45:07PM +0000, Christopher Lameter wrote:
> > I still think implicit exceptions to alignments are a bad idea. Those need
> > to be explicity specified and that is possible using kmem_cache_create().
>
> I swear we covered this last time the topic came up, but XFS would need
> to create special slab caches for each size between 512 and PAGE_SIZE.
> Potentially larger, depending on whether the MM developers are willing to
> guarantee that kmalloc(PAGE_SIZE * 2, GFP_KERNEL) will return a PAGE_SIZE
> aligned block of memory indefinitely.
Page size alignment of multi-page heap allocations is ncessary. The
current behaviour w/ KASAN is to offset so a 8KB allocation spans 3
pages and is not page aligned. That causes just as much in way
of alignment problems as unaligned objects in multi-object-per-page
slabs.
As I said in the lastest discussion of this problem on XFS (pmem
devices w/ KASAN enabled), all we -need- is a GFP flag that tells the
slab allocator to give us naturally aligned object or fail if it
can't. I don't care how that gets implemented (e.g. another set of
heap slabs like the -rcl slabs), I just don't want every high level
subsystem that allocates heap memory for IO buffers to have to
implement their own aligned slab caches.
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
next prev parent reply other threads:[~2019-08-28 22:24 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-26 11:16 [PATCH v2 0/2] guarantee natural alignment for kmalloc() Vlastimil Babka
2019-08-26 11:16 ` [PATCH v2 1/2] mm, sl[ou]b: improve memory accounting Vlastimil Babka
2019-08-26 11:16 ` [PATCH v2 2/2] mm, sl[aou]b: guarantee natural alignment for kmalloc(power-of-two) Vlastimil Babka
2019-08-28 18:45 ` Christopher Lameter
2019-08-28 19:46 ` Matthew Wilcox
2019-08-28 22:24 ` Dave Chinner [this message]
2019-08-29 7:56 ` Vlastimil Babka
2019-08-30 0:29 ` Dave Chinner
2019-08-29 7:39 ` Michal Hocko
2019-08-30 17:41 ` Christopher Lameter
2019-09-01 0:52 ` Matthew Wilcox
2019-09-03 20:13 ` Christopher Lameter
2019-09-03 20:53 ` Matthew Wilcox
2019-09-04 5:19 ` Christoph Hellwig
2019-09-04 6:40 ` Ming Lei
2019-09-04 7:20 ` Vlastimil Babka
2019-09-04 19:31 ` Christopher Lameter
2019-09-23 16:36 ` Vlastimil Babka
2019-09-23 17:17 ` David Sterba
2019-09-23 17:51 ` Darrick J. Wong
2019-09-24 20:47 ` cl
2019-09-24 20:51 ` Matthew Wilcox
2019-09-24 20:55 ` cl
2019-09-26 13:02 ` David Sterba
2019-09-24 21:19 ` Vlastimil Babka
2019-09-24 21:53 ` Dave Chinner
2019-09-24 22:21 ` Darrick J. Wong
2019-09-24 20:52 ` cl
2019-09-24 23:54 ` Andrew Morton
2019-09-25 7:17 ` Vlastimil Babka
2019-09-26 0:16 ` Christopher Lameter
2019-09-26 0:14 ` Christopher Lameter
2019-09-26 7:41 ` Vlastimil Babka
2019-09-28 1:12 ` Christopher Lameter
2019-09-30 13:32 ` Matthew Wilcox
2019-09-23 17:54 ` Roman Gushchin
2019-09-30 8:06 ` Christoph Hellwig
2019-09-30 9:23 ` Michal Hocko
2019-09-30 9:32 ` Kirill A. Shutemov
2019-09-23 18:57 ` Matthew Wilcox
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