On 07/20/2015 10:00 AM, Mel Gorman wrote:
[...]
> static bool __zone_watermark_ok(struct zone *z, unsigned int order,
> unsigned long mark, int classzone_idx, int alloc_flags,
> @@ -2259,7 +2261,7 @@ static bool __zone_watermark_ok(struct zone *z, unsigned int order,
> {
> long min = mark;
> int o;
> - long free_cma = 0;
> + const bool atomic = (alloc_flags & ALLOC_HARDER);
>
> /* free_pages may go negative - that's OK */
> free_pages -= (1 << order) - 1;
> @@ -2271,7 +2273,7 @@ static bool __zone_watermark_ok(struct zone *z, unsigned int order,
> * If the caller is not atomic then discount the reserves. This will
> * over-estimate how the atomic reserve but it avoids a search
> */
> - if (likely(!(alloc_flags & ALLOC_HARDER)))
> + if (likely(!atomic))
> free_pages -= z->nr_reserved_highatomic;
> else
> min -= min / 4;
> @@ -2279,22 +2281,30 @@ static bool __zone_watermark_ok(struct zone *z, unsigned int order,
> #ifdef CONFIG_CMA
> /* If allocation can't use CMA areas don't use free CMA pages */
> if (!(alloc_flags & ALLOC_CMA))
> - free_cma = zone_page_state(z, NR_FREE_CMA_PAGES);
> + free_pages -= zone_page_state(z, NR_FREE_CMA_PAGES);
> #endif
>
> - if (free_pages - free_cma <= min + z->lowmem_reserve[classzone_idx])
> + if (free_pages <= min + z->lowmem_reserve[classzone_idx])
> return false;
> - for (o = 0; o < order; o++) {
> - /* At the next order, this order's pages become unavailable */
> - free_pages -= z->free_area[o].nr_free << o;
>
> - /* Require fewer higher order pages to be free */
> - min >>= 1;
> + /* order-0 watermarks are ok */
> + if (!order)
> + return true;
> +
> + /* Check at least one high-order page is free */
> + for (o = order; o < MAX_ORDER; o++) {
> + struct free_area *area = &z->free_area[o];
> + int mt;
> +
> + if (atomic && area->nr_free)
> + return true;
This may be a false positive due to MIGRATE_CMA or MIGRATE_ISOLATE pages being
the only free ones. But maybe it doesn't matter that much?
>
> - if (free_pages <= min)
> - return false;
> + for (mt = 0; mt < MIGRATE_PCPTYPES; mt++) {
> + if (!list_empty(&area->free_list[mt]))
> + return true;
> + }
This may be a false negative for ALLOC_CMA allocations, if the only free pages
are of MIGRATE_CMA. Arguably that's the worse case than a false positive?
> }
> - return true;
> + return false;
> }
>
> bool zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark,
>
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