linux-kernel - Re: [PATCH v2] X86-32: Allocate 256 bytes for pgd in PAE paging

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Message-ID: <alpine.DEB.2.11.1412180850290.2593@gentwo.org>
Date:	Thu, 18 Dec 2014 08:52:40 -0600 (CST)
From:	Christoph Lameter <cl@...ux.com>
To:	Dave Hansen <dave.hansen@...el.com>
cc:	Fenghua Yu <fenghua.yu@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Ingo Molnar <mingo@...e.hu>,
	Glenn Williamson <glenn.p.williamson@...el.com>,
	linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [PATCH v2] X86-32: Allocate 256 bytes for pgd in PAE paging

On Wed, 17 Dec 2014, Dave Hansen wrote:

> IOW, do *ALL* of the sl*b allocators in all of their forms with all of
> their debugging options guarantee 32-byte alignment when allocating
> 256-byte objects?

No. For that the arch has to set a macro call ARCH_KMALLOC_MINALIGN or
ARCH_DMA_MINALIGN. Default alignment is to a word boundary.

> I know we at least try to align to a cacheline, which would be good
> enough, but I'm fuzzy on what we *guarantee*.

Sorry we only do this if requested for a slab cache.

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