On Thu, 4 May 2023 18:09:54 +0800 "zhaoyang.huang" <zhaoyang.huang@xxxxxxxxxx> wrote:
> From: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
>
> Let us look at the series of scenarios below with WMARK_LOW=25MB,WMARK_MIN=5MB
> (managed pages 1.9GB). We can know that current 'fixed 1/2 ratio' start to use
> CMA since C which actually has caused U&R lower than WMARK_LOW (this should be
> deemed as against current memory policy, that is, U&R should either stay around
> WATERMARK_LOW when no allocation or do reclaim via enter slowpath)
>
> free_cma/free_pages(MB) A(12/30) B(12/25) C(12/20)
> fixed 1/2 ratio N N Y
> this commit Y Y Y
A few style issues.
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3071,6 +3071,34 @@ 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)
This function would benefit from a nice covering comment. Explain what
it does and, especially, why it does it.
I'm not sure that "__if_use_cma_first" is a good name - I'd need to see
that explanation to decide.
> +{
> + unsigned long cma_proportion = 0;
> + unsigned long cma_free_proportion = 0;
> + unsigned long watermark = 0;
> + long count = 0;
> + bool cma_first = false;
We seems to have some unnecessary initializations here.
> + watermark = wmark_pages(zone, alloc_flags & ALLOC_WMARK_MASK);
> + /*check if GFP_MOVABLE pass previous watermark check via the help of CMA*/
Space after /* and before */
/*
* Check if GFP_MOVABLE passed the previous watermark check with the
* help of CMA
*/
> + if (!zone_watermark_ok(zone, order, watermark, 0, alloc_flags & (~ALLOC_CMA)))
> + /* WMARK_LOW failed lead to using cma first, this helps U&R stay
> + * around low when being drained by GFP_MOVABLE
> + */
Unusual layout, text is hard to understand. Maybe something like
/*
* WMARK_LOW failed, leading to the use cma first. This helps
* U&R stay low when <something> is being drained by
* GFP_MOVABLE
*/
Also, please expand "U&R" into full words. I don't recognize that
abbreviation.
> + cma_first = true;
> + else {
> + /*check proportion when zone_watermark_ok*/
/* check ... _ok */
Comments should seek to explain *why* a thing is being done, rather than
*what* is being done.
> + 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 >= cma_proportion * 2
> + || 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 +3115,10 @@ static bool unreserve_highatomic_pageblock(const struct alloc_context *ac,
I wonder why git decided this hunk is unreserve_highatomic_pageblock().
It's actually in __rmqueue().
> * 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;
Code could be tidier and could avoid needless 80-column wordwrapping
and an unneeded local.
page = NULL;
if (__if_use_cma_first(zone, order, alloc_flags))
page = __rmqueue_cma_fallback(zone, order);
> if (page)
> return page;
> }
Anyway, please take a look, fix the build error and send us a v3. I
suggest you cc Minchan Kim, who might review it for us.
