Hi Zhaoyang!
On Fri, Apr 28, 2023 at 07:00:41PM +0800, zhaoyang.huang wrote:
> From: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
>
> Please be notice bellowing typical scenario that commit 168676649 introduce,
> that is, 12MB free cma pages 'help' GFP_MOVABLE to keep draining/fragmenting
> U&R page blocks until they shrink to 12MB without enter slowpath which against
> current reclaiming policy. This commit change the criteria from hard coded '1/2'
> to watermark check which leave U&R free pages stay around WMARK_LOW when being
> fallback.
Can you, please, explain the problem you're solving in more details?
If I understand your code correctly, you're effectively reducing the
use of cma areas for movable allocations. Why it's good?
Also, this is a hot path, please, make sure you're not adding
much overhead.
And please use scripts/checkpatch.pl next time, there are many
code style issues.
Thanks!
>
> DMA32 free:25900kB boost:0kB min:4176kB low:25856kB high:29516kB
>
> Signed-off-by: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
> ---
> mm/page_alloc.c | 40 ++++++++++++++++++++++++++++++++++++----
> 1 file changed, 36 insertions(+), 4 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 0745aed..97768fe 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3071,6 +3071,39 @@ static bool unreserve_highatomic_pageblock(const struct alloc_context *ac,
>
> }
>
> +#ifdef CONFIG_CMA
> +static bool __if_use_cma_first(struct zone *zone, unsigned int order, unsigned int alloc_flags)
> +{
> + unsigned long cma_proportion = 0;
> + unsigned long cma_free_proportion = 0;
> + unsigned long watermark = 0;
> + unsigned long wm_fact[ALLOC_WMARK_MASK] = {1, 1, 2};
> + long count = 0;
> + bool cma_first = false;
> +
> + watermark = wmark_pages(zone, alloc_flags & ALLOC_WMARK_MASK);
> + /*check if GFP_MOVABLE pass previous watermark check via the help of CMA*/
> + if (!zone_watermark_ok(zone, order, watermark, 0, alloc_flags & (~ALLOC_CMA)))
> + {
> + alloc_flags &= ALLOC_WMARK_MASK;
> + /* WMARK_LOW failed lead to using cma first, this helps U&R stay
> + * around low when being drained by GFP_MOVABLE
> + */
> + if (alloc_flags <= ALLOC_WMARK_LOW)
> + cma_first = true;
> + /*check proportion for WMARK_HIGH*/
> + else {
> + count = atomic_long_read(&zone->managed_pages);
> + cma_proportion = zone->cma_pages * 100 / count;
> + cma_free_proportion = zone_page_state(zone, NR_FREE_CMA_PAGES) * 100
> + / zone_page_state(zone, NR_FREE_PAGES);
> + cma_first = (cma_free_proportion >= wm_fact[alloc_flags] * cma_proportion
> + || cma_free_proportion >= 50);
> + }
> + }
> + return cma_first;
> +}
> +#endif
> /*
> * Do the hard work of removing an element from the buddy allocator.
> * Call me with the zone->lock already held.
> @@ -3087,10 +3120,9 @@ static bool unreserve_highatomic_pageblock(const struct alloc_context *ac,
> * allocating from CMA when over half of the zone's free memory
> * is in the CMA area.
> */
> - if (alloc_flags & ALLOC_CMA &&
> - zone_page_state(zone, NR_FREE_CMA_PAGES) >
> - zone_page_state(zone, NR_FREE_PAGES) / 2) {
> - page = __rmqueue_cma_fallback(zone, order);
> + if (migratetype == MIGRATE_MOVABLE) {
> + bool cma_first = __if_use_cma_first(zone, order, alloc_flags);
> + page = cma_first ? __rmqueue_cma_fallback(zone, order) : NULL;
> if (page)
> return page;
> }
> --
> 1.9.1
>
>
