linux-kernel - Re: [PATCH] memblock: stop using implicit alignement to SMP_CACHE

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Message-Id: <59C9470E-F718-4A11-BC65-FD68901723AC@linux.vnet.ibm.com>
Date:   Fri, 05 Oct 2018 18:05:01 +0300
From:   Mike Rapoport <rppt@...ux.vnet.ibm.com>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        linux-mm@...ck.org
CC:     linux-mips@...ux-mips.org, Michal Hocko <mhocko@...e.com>,
        linux-ia64@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Richard Weinberger <richard@....at>,
        Russell King <linux@...linux.org.uk>,
        Ingo Molnar <mingo@...hat.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Matt Turner <mattst88@...il.com>, linux-um@...ts.infradead.org,
        linux-m68k@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Guan Xuetao <gxt@....edu.cn>,
        linux-arm-kernel@...ts.infradead.org,
        Chris Zankel <chris@...kel.net>,
        Michal Simek <monstr@...str.eu>,
        Tony Luck <tony.luck@...el.com>, linux-kernel@...r.kernel.org,
        Paul Burton <paul.burton@...s.com>,
        linux-alpha@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH] memblock: stop using implicit alignement to SMP_CACHE_BYTES



On October 5, 2018 6:25:38 AM GMT+03:00, Benjamin Herrenschmidt <benh@...nel.crashing.org> wrote:
>On Fri, 2018-10-05 at 00:07 +0300, Mike Rapoport wrote:
>> When a memblock allocation APIs are called with align = 0, the
>alignment is
>> implicitly set to SMP_CACHE_BYTES.
>> 
>> Replace all such uses of memblock APIs with the 'align' parameter
>explicitly
>> set to SMP_CACHE_BYTES and stop implicit alignment assignment in the
>> memblock internal allocation functions.
>> 
>> For the case when memblock APIs are used via helper functions, e.g.
>like
>> iommu_arena_new_node() in Alpha, the helper functions were detected
>with
>> Coccinelle's help and then manually examined and updated where
>appropriate.
>> 
>> The direct memblock APIs users were updated using the semantic patch
>below:
>
>What is the purpose of this ? It sounds rather counter-intuitive...

Why?
I think it actually more intuitive to explicitly set alignment to SMP_CACHE_BYTES rather than use align = 0 because deeply inside allocator it will be implicitly reset to SMP_CACHE_BYTES...

>Ben.

-- 
Sincerely yours,
Mike.