On 6/3/21 2:34 PM, Mel Gorman wrote:
>
>> > @@ -687,10 +687,53 @@ static void bad_page(struct page *page, const char *reason)
>> > add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
>> > }
>> >
>> > +static inline unsigned int order_to_pindex(int migratetype, int order)
>> > +{
>> > + int base = order;
>> > +
>> > +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
>> > + if (order > PAGE_ALLOC_COSTLY_ORDER) {
>> > + VM_BUG_ON(order != pageblock_order);
>> > + base = PAGE_ALLOC_COSTLY_ORDER + 1;
>> > + }
>> > +#else
>> > + VM_BUG_ON(order > PAGE_ALLOC_COSTLY_ORDER);
>> > +#endif
>> > +
>> > + return (MIGRATE_PCPTYPES * base) + migratetype;
>> > +}
>> > +
>> > +static inline int pindex_to_order(unsigned int pindex)
>> > +{
>> > + int order = pindex / PAGE_ALLOC_COSTLY_ORDER;
>>
>> This seems wrong, shouldn't we divide by MIGRATE_PCPTYPES?
>> It just happens to be the same number, so testing won't flag this.
>>
>
> Whoops, yes, basic algebra says you're right so well spotted. If
> PAGE_ALLOC_COSTLY_ORDER ever changed for some reason, this would blow up.
>
> So this?
Yeah, great!
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index bbe05289b121..f1bed5b847ec 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -345,11 +345,11 @@ enum zone_watermarks {
> #define NR_PCP_LISTS (MIGRATE_PCPTYPES * (PAGE_ALLOC_COSTLY_ORDER + 1 + NR_PCP_THP))
>
> /*
> - * Shift to encode migratetype in order in the least significant bits and
> - * migratetype in the higher bits.
> + * Shift to encode migratetype and order in the same integer, with order
> + * in the least significant bits.
> */
> -#define NR_PCP_ORDER_SHIFT 8
> -#define NR_PCP_ORDER_MASK ((1<<NR_PCP_ORDER_SHIFT) - 1)
> +#define NR_PCP_ORDER_WIDTH 8
> +#define NR_PCP_ORDER_MASK ((1<<NR_PCP_ORDER_WIDTH) - 1)
>
> #define min_wmark_pages(z) (z->_watermark[WMARK_MIN] + z->watermark_boost)
> #define low_wmark_pages(z) (z->_watermark[WMARK_LOW] + z->watermark_boost)
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 49f3c7dcdfca..7be71f9ad9f0 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -694,7 +694,7 @@ static inline unsigned int order_to_pindex(int migratetype, int order)
>
> static inline int pindex_to_order(unsigned int pindex)
> {
> - int order = pindex / PAGE_ALLOC_COSTLY_ORDER;
> + int order = pindex / MIGRATE_PCPTYPES;
>
> #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> if (order > PAGE_ALLOC_COSTLY_ORDER) {
> @@ -1487,7 +1487,7 @@ static void free_pcppages_bulk(struct zone *zone, int count,
> batch_free = count;
>
> order = pindex_to_order(pindex);
> - BUILD_BUG_ON(MAX_ORDER >= (1<<NR_PCP_ORDER_SHIFT));
> + BUILD_BUG_ON(MAX_ORDER >= (1<<NR_PCP_ORDER_WIDTH));
> do {
> page = list_last_entry(list, struct page, lru);
> /* must delete to avoid corrupting pcp list */
> @@ -1499,7 +1499,7 @@ static void free_pcppages_bulk(struct zone *zone, int count,
> continue;
>
> /* Encode order with the migratetype */
> - page->index <<= NR_PCP_ORDER_SHIFT;
> + page->index <<= NR_PCP_ORDER_WIDTH;
> page->index |= order;
>
> list_add_tail(&page->lru, &head);
> @@ -1537,7 +1537,7 @@ static void free_pcppages_bulk(struct zone *zone, int count,
>
> /* mt has been encoded with the order (see above) */
> order = mt & NR_PCP_ORDER_MASK;
> - mt >>= NR_PCP_ORDER_SHIFT;
> + mt >>= NR_PCP_ORDER_WIDTH;
>
> /* MIGRATE_ISOLATE page should not go to pcplists */
> VM_BUG_ON_PAGE(is_migrate_isolate(mt), page);
>
>
>
