Re: [PATCH] arm64: Increase the max granular size

From: Joonsoo Kim <iamjoonsoo.kim@lge.com>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christoph Lameter <cl@linux.com>,
	Robert Richter <rric@kernel.org>,
	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: Thu, 5 Nov 2015 13:31:55 +0900	[thread overview]
Message-ID: <20151105043155.GA20374@js1304-P5Q-DELUXE> (raw)
In-Reply-To: <20151104153910.GN7637@e104818-lin.cambridge.arm.com>

On Wed, Nov 04, 2015 at 03:39:10PM +0000, Catalin Marinas wrote:
> On Wed, Nov 04, 2015 at 09:28:34AM -0600, Christoph Lameter wrote:
> > On Wed, 4 Nov 2015, Catalin Marinas wrote:
> > 
> > > 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.
> > 
> > Ok maybe add some BUILD_BUG_ONs to ensure that builds fail until we have
> > addressed that.
> 
> A BUILD_BUG_ON should be fine.
> 
> Thinking some more, I think if KMALLOC_MIN_SIZE is 128, there is no gain
> with off-slab management since the freelist allocation would still be
> 128 bytes. An alternative to reverting while still having a little
> benefit of off-slab for 256 bytes objects (rather than 512 as we would
> get with the revert):
> 
> diff --git a/mm/slab.c b/mm/slab.c
> index 4fcc5dd8d5a6..ac32b4a0f2ec 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -2212,8 +2212,8 @@ __kmem_cache_create (struct kmem_cache *cachep, unsigned long flags)
>  	 * it too early on. Always use on-slab management when
>  	 * SLAB_NOLEAKTRACE to avoid recursive calls into kmemleak)
>  	 */
> -	if ((size >= (PAGE_SIZE >> 5)) && !slab_early_init &&
> -	    !(flags & SLAB_NOLEAKTRACE))
> +	if ((size >= (PAGE_SIZE >> 5)) && (size > KMALLOC_MIN_SIZE) &&
> +		!slab_early_init && !(flags & SLAB_NOLEAKTRACE))
>  		/*
>  		 * Size is large, assume best to place the slab management obj
>  		 * off-slab (should allow better packing of objs).
> 
> Whichever you prefer.

Hello,

I prefer this simple way. It looks like that it can solve the issue on
any arbitrary configuration.

Thanks.