linux-kernel - Re: [PATCH v1 2/5] mm/memory_hotplug: enforce section alignment when onlining/offlining

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Message-ID: <20180816123433.GB16861@techadventures.net>
Date:   Thu, 16 Aug 2018 14:34:33 +0200
From:   Oscar Salvador <osalvador@...hadventures.net>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Pavel Tatashin <pasha.tatashin@...cle.com>,
        Kemi Wang <kemi.wang@...el.com>,
        David Rientjes <rientjes@...gle.com>,
        Jia He <jia.he@...-semitech.com>,
        Oscar Salvador <osalvador@...e.de>,
        Petr Tesarik <ptesarik@...e.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Mathieu Malaterre <malat@...ian.org>,
        Baoquan He <bhe@...hat.com>,
        Wei Yang <richard.weiyang@...il.com>,
        Ross Zwisler <zwisler@...nel.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH v1 2/5] mm/memory_hotplug: enforce section alignment when
 onlining/offlining

On Thu, Aug 16, 2018 at 12:06:25PM +0200, David Hildenbrand wrote:
> onlining/offlining code works on whole sections, so let's enforce that.
> Existing code only allows to add memory in memory block size. And only
> whole memory blocks can be onlined/offlined. Memory blocks are always
> aligned to sections, so this should not break anything.
> 
> online_pages/offline_pages will implicitly mark whole sections
> online/offline, so the code really can only handle such granularities.
> 
> (especially offlining code cannot deal with pageblock_nr_pages but
>  theoretically only MAX_ORDER-1)
> 
> Signed-off-by: David Hildenbrand <david@...hat.com>

Hi David,

If you are really willing to move the checks from this patch[1] to
online/offline_pages, you might consider to put that in as well.
So we have a function that checks for everything, and not multiple checks.

Another thing is that I would have prefered to take the checks up to
memory_block_action, but offline_pages gets also called from ppc-memtrace code.

Other than that, 

Reviewed-by: Oscar Salvador <osalvador@...e.de>


[1] https://patchwork.kernel.org/patch/10567277/

Thanks
-- 
Oscar Salvador
SUSE L3