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From: Oscar Salvador <osalvador@suse.de>
To: Qian Cai <cai@lca.pw>
Cc: akpm@linux-foundation.org, mhocko@kernel.org, vbabka@suse.cz,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] mm/hotplug: fix offline undo_isolate_page_range()
Date: Thu, 14 Mar 2019 09:09:22 +0100
Message-ID: <20190314080922.dk5ljg7fbtarzrog@d104.suse.de> (raw)
In-Reply-To: <20190313143133.46200-1-cai@lca.pw>

On Wed, Mar 13, 2019 at 10:31:33AM -0400, Qian Cai wrote:
> Also, after calling the "useless" undo_isolate_page_range() here, it
> reaches the point of no returning by notifying MEM_OFFLINE. Those pages
> will be marked as MIGRATE_MOVABLE again once onlining. The only thing
> left to do is to decrease the number of isolated pageblocks zone
> counter which would make some paths of the page allocation slower that
> the above commit introduced. A memory block is usually at most 1GiB in
> size, so an "int" should be enough to represent the number of pageblocks
> in a block. Fix an incorrect comment along the way.

Well, x86_64's memblocks can be up to 2GB depending on the memory we got.
Plus the fact that alloc_contig_range can be used to isolate 16GB-hugetlb
pages on powerpc, and that could be a lot of pageblocks.

While an "int" could still hold, I think we should use "long" just to be
more future-proof.

> 
> Fixes: 2ce13640b3f4 ("mm: __first_valid_page skip over offline pages")
> Signed-off-by: Qian Cai <cai@lca.pw>
> ---
> 
> v2: return the nubmer of isolated pageblocks in start_isolate_page_range() per
>     Oscar; take the zone lock when undoing zone->nr_isolate_pageblock per
>     Michal.
> 
>  mm/memory_hotplug.c | 17 +++++++++++++----
>  mm/page_alloc.c     |  2 +-
>  mm/page_isolation.c | 16 ++++++++++------
>  mm/sparse.c         |  2 +-
>  4 files changed, 25 insertions(+), 12 deletions(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index cd23c081924d..8ffe844766da 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1580,7 +1580,7 @@ static int __ref __offline_pages(unsigned long start_pfn,
>  {
>  	unsigned long pfn, nr_pages;
>  	long offlined_pages;
> -	int ret, node;
> +	int ret, node, count;

I would rather use a meaningful name here, like "nr_isolated_pageblocks" or
something like that.
 

-- 
Oscar Salvador
SUSE L3


  parent reply index

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-03-13 14:31 Qian Cai
2019-03-14  8:05 ` Michal Hocko
2019-03-14  8:09 ` Oscar Salvador [this message]
2019-03-14  8:22   ` Michal Hocko
2019-03-14  8:10 ` Oscar Salvador

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