Re: [PATCH 1/2] mm, page_alloc: Keep pcp count and list contents in sync if struct page is corrupted

["Hillf Danton" <hillf.zj@alibaba-inc.com>]

On Friday, December 02, 2016 2:19 PM Vlastimil Babka wrote:
> On 12/02/2016 04:47 AM, Hillf Danton wrote:
> > On Friday, December 02, 2016 8:23 AM Mel Gorman wrote:
> >> Vlastimil Babka pointed out that commit 479f854a207c ("mm, page_alloc:
> >> defer debugging checks of pages allocated from the PCP") will allow the
> >> per-cpu list counter to be out of sync with the per-cpu list contents
> >> if a struct page is corrupted. This patch keeps the accounting in sync.
> >>
> >> Fixes: 479f854a207c ("mm, page_alloc: defer debugging checks of pages allocated from the PCP")
> >> Signed-off-by: Mel Gorman <mgorman@suse.de>
> >> cc: stable@vger.kernel.org [4.7+]
> 
> Acked-by: Vlastimil Babka <vbabka@suse.cz>
> 
> >> ---
> >>  mm/page_alloc.c | 5 +++--
> >>  1 file changed, 3 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> >> index 6de9440e3ae2..777ed59570df 100644
> >> --- a/mm/page_alloc.c
> >> +++ b/mm/page_alloc.c
> >> @@ -2192,7 +2192,7 @@ static int rmqueue_bulk(struct zone *zone, unsigned int order,
> >>  			unsigned long count, struct list_head *list,
> >>  			int migratetype, bool cold)
> >>  {
> >> -	int i;
> >> +	int i, alloced = 0;
> >>
> >>  	spin_lock(&zone->lock);
> >>  	for (i = 0; i < count; ++i) {
> >> @@ -2217,13 +2217,14 @@ static int rmqueue_bulk(struct zone *zone, unsigned int order,
> >>  		else
> >>  			list_add_tail(&page->lru, list);
> >>  		list = &page->lru;
> >> +		alloced++;
> >>  		if (is_migrate_cma(get_pcppage_migratetype(page)))
> >>  			__mod_zone_page_state(zone, NR_FREE_CMA_PAGES,
> >>  					      -(1 << order));
> >>  	}
> >>  	__mod_zone_page_state(zone, NR_FREE_PAGES, -(i << order));
> >
> > Now i is a pure index, yes?
> 
> No, even if a page fails the check_pcp_refill() check and is not
> "allocated", it is also no longer a free page, so it's correct to
> subtract it from NR_FREE_PAGES.
> 
Yes, we can allocate free page   next time.

thanks
Hillf


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