From: Vineet Gupta <vineet.gupta1@synopsys.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: David Laight <David.Laight@ACULAB.COM>,
Alexey Brodkin <alexey.brodkin@synopsys.com>,
"linux-snps-arc@lists.infradead.org"
<linux-snps-arc@lists.infradead.org>,
Arnd Bergmann <arnd.bergmann@linaro.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"stable@vger.kernel.org" <stable@vger.kernel.org>,
Mark Rutland <mark.rutland@arm.com>
Subject: Re: [PATCH] ARC: Explicitly set ARCH_SLAB_MINALIGN = 8
Date: Wed, 13 Feb 2019 15:23:36 -0800 [thread overview]
Message-ID: <e6138aeb-9ce4-fbfa-4d6a-b76f189a3e47@synopsys.com> (raw)
In-Reply-To: <20190213125651.GP32494@hirez.programming.kicks-ass.net>
On 2/13/19 4:56 AM, Peter Zijlstra wrote:
>
> Personally I think u64 and company should already force natural
> alignment; but alas.
But there is an ISA/ABI angle here too. e.g. On 32-bit ARC, LDD (load double) is
allowed to take a 32-bit aligned address to load a register pair. Thus all u64
need not be 64-bit aligned (unless attribute aligned 8 etc) hence the relaxation
in ABI (alignment of long long is 4). You could certainly argue that we end up
undoing some of it anyways by defining things like ARCH_KMALLOC_MINALIGN to 8, but
still...
> I though that was part of the reason we have __u64
> and co., so that ABI is invariant to kernel alignment changes.
Apparently not.
>>> I suspect the slab allocator should be returning 8 byte aligned addresses
>>> on all systems....
>>
>> why ? As I understand it is still not fool proof against the expected alignment of
>> inner members. There ought to be a better way to enforce all this.
>
> I agree that for ARC ARCH_SLAB_MINALIGN should be at least 8.
This issue aside, are there other reasons ? Because making it 8 on ARC is just
pending the eventuality for later.
next prev parent reply other threads:[~2019-02-13 23:24 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-08 10:55 [PATCH] ARC: Explicitly set ARCH_SLAB_MINALIGN = 8 Alexey Brodkin
2019-02-12 17:17 ` Vineet Gupta
2019-02-12 17:30 ` David Laight
2019-02-12 17:45 ` Vineet Gupta
2019-02-13 12:56 ` Peter Zijlstra
2019-02-13 14:13 ` David Laight
2019-02-13 23:23 ` Vineet Gupta [this message]
2019-02-14 8:50 ` Alexey Brodkin
2019-02-14 10:28 ` Peter Zijlstra
2019-02-15 1:34 ` Vineet Gupta
2019-02-18 8:53 ` Alexey Brodkin
2019-02-19 23:30 ` Vineet Gupta
2019-02-14 10:31 ` Peter Zijlstra
2019-02-14 10:44 ` Alexey Brodkin
2019-02-14 11:08 ` Peter Zijlstra
2019-02-14 12:05 ` Alexey Brodkin
2019-02-14 12:24 ` Peter Zijlstra
2019-02-14 14:14 ` David Laight
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