Messages in this thread | | | Subject | Re: [PATCH] mm: page_alloc: High-order per-cpu page allocator v4 | From | Vlastimil Babka <> | Date | Thu, 1 Dec 2016 14:41:29 +0100 |
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On 12/01/2016 01:24 AM, Mel Gorman wrote:
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> @@ -1096,28 +1097,29 @@ static void free_pcppages_bulk(struct zone *zone, int count, > if (nr_scanned) > __mod_node_page_state(zone->zone_pgdat, NR_PAGES_SCANNED, -nr_scanned); > > - while (count) { > + while (count > 0) { > struct page *page; > struct list_head *list; > + unsigned int order; > > /* > * Remove pages from lists in a round-robin fashion. A > * batch_free count is maintained that is incremented when an > - * empty list is encountered. This is so more pages are freed > - * off fuller lists instead of spinning excessively around empty > - * lists > + * empty list is encountered. This is not exact due to > + * high-order but percision is not required. > */ > do { > batch_free++; > - if (++migratetype == MIGRATE_PCPTYPES) > - migratetype = 0; > - list = &pcp->lists[migratetype]; > + if (++pindex == NR_PCP_LISTS) > + pindex = 0; > + list = &pcp->lists[pindex]; > } while (list_empty(list)); > > /* This is the only non-empty list. Free them all. */ > - if (batch_free == MIGRATE_PCPTYPES) > + if (batch_free == NR_PCP_LISTS) > batch_free = count; > > + order = pindex_to_order(pindex); > do { > int mt; /* migratetype of the to-be-freed page */ > > @@ -1135,11 +1137,14 @@ static void free_pcppages_bulk(struct zone *zone, int count, > if (bulkfree_pcp_prepare(page)) > continue;
Hmm I think that if this hits, we don't decrease count/increase nr_freed and pcp->count will become wrong. And if we are unlucky/doing full drain, all lists will get empty, but as count stays e.g. 1, we loop forever on the outer while()?
BTW, I think there's a similar problem (but not introduced by this patch) in rmqueue_bulk() and its
if (unlikely(check_pcp_refill(page))) continue;
This might result in pcp->count being higher than actual pages. That one would be introduced by 479f854a207c ("mm, page_alloc: defer debugging checks of pages allocated from the PCP").
> > - __free_one_page(page, page_to_pfn(page), zone, 0, mt); > - trace_mm_page_pcpu_drain(page, 0, mt); > - } while (--count && --batch_free && !list_empty(list)); > + __free_one_page(page, page_to_pfn(page), zone, order, mt); > + trace_mm_page_pcpu_drain(page, order, mt); > + nr_freed += (1 << order); > + count -= (1 << order); > + } while (count > 0 && --batch_free && !list_empty(list)); > } > spin_unlock(&zone->lock); > + pcp->count -= nr_freed; > } > > static void free_one_page(struct zone *zone,
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