Re: [PATCH v2] mm/hugetlb: fix set_max_huge_pages() when there are surplus pages

[Oscar Salvador <osalvador@suse.de>]

On Thu, Apr 03, 2025 at 04:26:36PM +0200, Oscar Salvador wrote:
> Unfortunately, this will not fly.

I did not spend much time, but solving the problem of hvo free pages
becoming surplus not being accounted twice, should not the following
fix the entire problem?

 diff --git a/mm/hugetlb.c b/mm/hugetlb.c
 index 39f92aad7bd1..6e9534a825ed 100644
 --- a/mm/hugetlb.c
 +++ b/mm/hugetlb.c
 @@ -3825,6 +3825,7 @@ static int adjust_pool_surplus(struct hstate *h, nodemask_t *nodes_allowed,
  static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
  			      nodemask_t *nodes_allowed)
  {
 +	unsigned long substract;
  	unsigned long min_count;
  	unsigned long allocated;
  	struct folio *folio;
 @@ -3960,7 +3961,12 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
  	 * and won't grow the pool anywhere else. Not until one of the
  	 * sysctls are changed, or the surplus pages go out of use.
  	 */
 -	min_count = h->resv_huge_pages + h->nr_huge_pages - h->free_huge_pages;
 +	if (h->free_huge_pages > persistent_huge_pages(h))
 +		substract = h->free_huge_pages - h->surplus_huge_pages;
 +	else
 +		h->free_huge_pages;
 +
 +	min_count = h->resv_huge_pages + persistent_huge_pages(h) - substract;
  	min_count = max(count, min_count);
  	try_to_free_low(h, min_count, nodes_allowed);


-- 
Oscar Salvador
SUSE Labs