On Sat, May 06, 2023 at 02:45:47PM +0800, zhaoyang.huang 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, UNMOVABLE & RECLAIMABLE should
> either stay around WATERMARK_LOW when no allocation or do reclaim via entering
> slowpath)
>
> -- Free_pages
> |
> |
> -- WMARK_LOW
> |
> -- Free_CMA
> |
> |
> --
>
> 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
>
> Signed-off-by: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
> ---
> v2: do proportion check when zone_watermark_ok, update commit message
> v3: update coding style and simplify the logic when zone_watermark_ok
We're getting closer, thank you for working on it.
> ---
> ---
> mm/page_alloc.c | 46 ++++++++++++++++++++++++++++++++++++++++------
> 1 file changed, 40 insertions(+), 6 deletions(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 0745aed..7aca49d 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -3071,6 +3071,41 @@ static bool unreserve_highatomic_pageblock(const struct alloc_context *ac,
>
> }
>
> +#ifdef CONFIG_CMA
> +/*
> + * GFP_MOVABLE allocation could drain UNMOVABLE & RECLAIMABLE page blocks via
> + * the help of CMA which makes GFP_KERNEL failed. Checking if zone_watermark_ok
> + * again without ALLOC_CMA to see if to use CMA first.
> + */
> +static bool __if_use_cma_first(struct zone *zone, unsigned int order, unsigned int alloc_flags)
Can you, please, rename it to use_cma_first()?
> +{
> + unsigned long watermark;
> + bool cma_first = false;
> +
> + watermark = wmark_pages(zone, alloc_flags & ALLOC_WMARK_MASK);
> + /* check if GFP_MOVABLE pass previous zone_watermark_ok via the help of CMA */
> + if (!zone_watermark_ok(zone, order, watermark, 0, alloc_flags & (~ALLOC_CMA)))
Please, add {} for both "if" and "else" parts. Also, please, invert the order to make it
easier to follow:
if (zone_watermark_ok(...)) {
...
} else {
...
}
> + /*
> + * watermark failed means UNMOVABLE & RECLAIMBLE is not enough
> + * now, we should use cma first to keep them stay around the
> + * corresponding watermark
> + */
> + cma_first = true;
> + else
> + /*
> + * remain previous fixed 1/2 logic when watermark ok as we have
Nobody knows what was previously here once your change is applied. Please, do not refer
to the previous state, add a comment about the current state. You can probably (partially)
move the comment from __rmqueue().
> + * above protection now
> + */
> + cma_first = (zone_page_state(zone, NR_FREE_CMA_PAGES) >
> + zone_page_state(zone, NR_FREE_PAGES) / 2);
> + return cma_first;
> +}
> +#else
> +static bool __if_use_cma_first(struct zone *zone, unsigned int order, unsigned int alloc_flags)
> +{
> + return false;
> +}
> +#endif
> /*
> * Do the hard work of removing an element from the buddy allocator.
> * Call me with the zone->lock already held.
> @@ -3084,13 +3119,12 @@ static bool unreserve_highatomic_pageblock(const struct alloc_context *ac,
> if (IS_ENABLED(CONFIG_CMA)) {
> /*
> * Balance movable allocations between regular and CMA areas by
> - * allocating from CMA when over half of the zone's free memory
> - * is in the CMA area.
> + * allocating from CMA base on judging zone_watermark_ok again
> + * to see if the latest check got pass via the help of CMA
> */
> - 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) {
> + page = __if_use_cma_first(zone, order, alloc_flags) ?
> + __rmqueue_cma_fallback(zone, order) : NULL;
Can you put it like
if (migratetype == MIGRATE_MOVABLE && use_cma_first(...)) {
page = ...
if (page)
return page;
}
to avoid using a ternary operator without a good reason?
Thanks!
