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SubjectRe: [PATCH v2] mm/hotplug: fix offline undo_isolate_page_range()
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

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