Re: [PATCH 2/4] mm: prevent double decrease of nr_reserved_highatomic
From: Mel Gorman
Date: Wed Oct 12 2016 - 02:54:32 EST
On Fri, Oct 07, 2016 at 02:45:34PM +0900, Minchan Kim wrote:
> There is race between page freeing and unreserved highatomic.
> CPU 0 CPU 1
> mt = get_pfnblock_migratetype
> set_pcppage_migratetype(page, mt)
> __free_one_page(mt) <- mt is stale
> By above race, a page on CPU 0 could go non-highorderatomic free list
> since the pageblock's type is changed. By that, unreserve logic of
> highorderatomic can decrease reserved count on a same pageblock
> several times and then it will make mismatch between
> nr_reserved_highatomic and the number of reserved pageblock.
> So, this patch verifies whether the pageblock is highatomic or not
> and decrease the count only if the pageblock is highatomic.
> Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
Acked-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>