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

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Date:   Thu, 30 Aug 2018 22:14:01 +0000
From:   Pasha Tatashin <Pavel.Tatashin@...rosoft.com>
To:     David Hildenbrand <david@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     "linux-mm@...ck.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

Hi David,

I am not sure this is needed, because we already have a stricter checker:

check_hotplug_memory_range()

You could call it from online_pages(), if you think there is a reason to
do it, but other than that it is done from add_memory_resource() and
from remove_memory().

Thank you,
Pavel

On 8/16/18 6:06 AM, 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>
> ---
>  mm/memory_hotplug.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 090cf474de87..30d2fa42b0bb 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -897,6 +897,11 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_typ
>  	struct memory_notify arg;
>  	struct memory_block *mem;
>  
> +	if (!IS_ALIGNED(pfn, PAGES_PER_SECTION))
> +		return -EINVAL;
> +	if (!IS_ALIGNED(nr_pages, PAGES_PER_SECTION))
> +		return -EINVAL;
> +
>  	/*
>  	 * We can't use pfn_to_nid() because nid might be stored in struct page
>  	 * which is not yet initialized. Instead, we find nid from memory block.
> @@ -1600,10 +1605,9 @@ int offline_pages(unsigned long start_pfn, unsigned long nr_pages)
>  	struct zone *zone;
>  	struct memory_notify arg;
>  
> -	/* at least, alignment against pageblock is necessary */
> -	if (!IS_ALIGNED(start_pfn, pageblock_nr_pages))
> +	if (!IS_ALIGNED(start_pfn, PAGES_PER_SECTION))
>  		return -EINVAL;
> -	if (!IS_ALIGNED(end_pfn, pageblock_nr_pages))
> +	if (!IS_ALIGNED(nr_pages, PAGES_PER_SECTION))
>  		return -EINVAL;
>  	/* This makes hotplug much easier...and readable.
>  	   we assume this for now. .*/
>