From: Catalin Marinas <catalin.marinas@arm.com>
To: Christoph Lameter <cl@linux.com>
Cc: Robert Richter <rric@kernel.org>, Joonsoo Kim <js1304@gmail.com>,
Linux-sh list <linux-sh@vger.kernel.org>,
Will Deacon <will.deacon@arm.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Robert Richter <rrichter@cavium.com>,
linux-mm@kvack.org,
Tirumalesh Chalamarla <tchalamarla@cavium.com>,
Geert Uytterhoeven <geert@linux-m68k.org>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH] arm64: Increase the max granular size
Date: Wed, 4 Nov 2015 14:54:46 +0000 [thread overview]
Message-ID: <20151104145445.GL7637@e104818-lin.cambridge.arm.com> (raw)
In-Reply-To: <alpine.DEB.2.20.1511040748590.17248@east.gentwo.org>
On Wed, Nov 04, 2015 at 07:53:50AM -0600, Christoph Lameter wrote:
> On Wed, 4 Nov 2015, Catalin Marinas wrote:
>
> > The simplest option would be to make sure that off slab isn't allowed
> > for caches of KMALLOC_MIN_SIZE or smaller, with the drawback that not
> > only "kmalloc-128" but any other such caches will be on slab.
>
> The reason for an off slab configuration is denser object packing.
>
> > I think a better option would be to first check that there is a
> > kmalloc_caches[] entry for freelist_size before deciding to go off-slab.
>
> Hmmm.. Yes seems to be an option.
>
> Maybe we simply revert commit 8fc9cf420b36 instead?
I'm fine with this. Also note that the arm64 commit changing
L1_CACHE_BYTES to 128 hasn't been pushed yet (it's queued for 4.4).
> That does not seem to make too much sense to me and the goal of the
> commit cannot be accomplished on ARM. Your patch essentially reverts
> the effect anyways.
In theory it only reverts the effect for the first kmalloc_cache
("kmalloc-128" in the arm64 case). Any other bigger cache which would
not be mergeable with an existing one still has the potential of
off-slab management.
> Smaller slabs really do not need off slab management anyways since they
> will only loose a few objects per slab page.
IIUC, starting with 128 slab size for a 4KB page, you have 32 objects
per page. The freelist takes 32 bytes (or 31), therefore you waste a
single slab object. However, only 1/4 of it is used for freelist and the
waste gets bigger with 256 slab size, hence the original commit.
BTW, assuming L1_CACHE_BYTES is 512 (I don't ever see this happening but
just in theory), we potentially have the same issue. What would save us
is that INDEX_NODE would match the first "kmalloc-512" cache, so we have
it pre-populated.
--
Catalin
next prev parent reply other threads:[~2015-11-04 14:54 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-22 17:59 [PATCH] arm64: Increase the max granular size Robert Richter
2015-09-22 18:29 ` Will Deacon
2015-09-25 14:45 ` Robert Richter
2015-09-25 16:31 ` Tirumalesh Chalamarla
2015-10-10 17:39 ` Timur Tabi
2015-10-12 9:16 ` Will Deacon
2015-10-16 19:57 ` Timur Tabi
2015-10-28 19:09 ` Catalin Marinas
2015-11-03 11:07 ` Geert Uytterhoeven
2015-11-03 12:05 ` Catalin Marinas
2015-11-03 14:38 ` Catalin Marinas
2015-11-03 14:55 ` Geert Uytterhoeven
2015-11-03 18:50 ` Catalin Marinas
2015-11-03 23:33 ` Christoph Lameter
2015-11-04 12:36 ` Catalin Marinas
2015-11-04 13:53 ` Christoph Lameter
2015-11-04 14:54 ` Catalin Marinas [this message]
2015-11-04 15:28 ` Christoph Lameter
2015-11-04 15:39 ` Catalin Marinas
2015-11-05 4:31 ` Joonsoo Kim
2015-11-05 11:50 ` [PATCH] mm: slab: Only move management objects off-slab for sizes larger than KMALLOC_MIN_SIZE Catalin Marinas
2015-11-05 13:31 ` Andrew Morton
2015-11-05 16:08 ` Catalin Marinas
2015-11-06 13:00 ` Geert Uytterhoeven
2015-11-05 17:39 ` Christoph Lameter
2015-11-05 4:40 ` [PATCH] arm64: Increase the max granular size Joonsoo Kim
2015-11-05 10:32 ` Catalin Marinas
2015-11-05 11:45 ` Joonsoo Kim
2015-11-05 12:17 ` Catalin Marinas
2015-11-09 7:41 ` Joonsoo Kim
2015-11-09 18:36 ` Catalin Marinas
2015-11-10 0:19 ` Joonsoo Kim
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