Re: [PATCH 1/2] mm/hugetlb: Prefer mempolicy nodes for calcuating surplus hugepage reservation

[Joshua Hahn <joshua.hahnjy@gmail.com>]

On Tue,  7 Jul 2026 12:28:55 -0600 Charles Haithcock <chaithco@redhat.com> wrote:

> Currently, reserving surplus hugetlb pages in a mempolicy still use
> global counters for calculating how many hugetlb pages to reserve.
> Modify this to consider the nodes in the mempolicy first but fall back
> to all possible nodes.

Hi Charles, thank you for the patch, this looks good to me!

Personally I like the description of the commit in the cover letter
because it provides a bit more context. Do other reviewers have
thoughts on this? In any case, the code LGTM : -)

Reviewed-by: Joshua Hahn <joshua.hahnjy@gmail.com>

BTW this is a little strange but Sashiko seems to have failed to apply
this patch [1] which is strange because when applying on the exact
same commit db6ed2a3d3106 "mm/swap, PM: hibernate: atomically replace hibernation pin"
as Sashiko tried, it worked & compiled for me with no errors at all...

[1] https://sashiko.dev/#/patchset/20260707182900.483757-1-chaithco%40redhat.com
Sashiko's error log:

Trying baseline: mm/mm-new (db6ed2a3d31068ca5577466591b2521dee0508ca)
Patch 41962/2 (ID: 108031) failed to apply.
Application failed.

> Suggested-by: Joshua Hahn <joshua.hahnjy@gmail.com>
> Signed-off-by: Charles Haithcock <chaithco@redhat.com>
> ---
> 
> - v1: Modified `needed` calculation to use `allowed_mems_nr(h)` in order
>   to consider free hugetlb pages in our mempolicy.
> - v2: Folded in Joshua Hahn's recommendation [1] to further modify
>   `needed` calculation to take the max of either the available hugetlb
>   pages in the mempolicy or the globally available hugetlb pages. Allows
>   allocations to prioritize nodes in the mempolicy but can still fall
>   back to offnode allocations. Also added selftests to check only for 
>   the edgecase which caused this to initially be reported and sanity
>   checks.
> - v3: Split the change and tests into separate patches and clean up code
>   to better align with kernel style guidelines. Likewise, fold in Usama
>   Arif's correction [2].
> 
> [1] https://lore.kernel.org/all/20260602152022.2673803-1-joshua.hahnjy@gmail.com/
> [2] https://lore.kernel.org/linux-mm/20260624144600.8159-1-usama.arif@linux.dev/
> 
>  mm/hugetlb.c | 42 ++++++++++++++++++++++--------------------
>  1 file changed, 22 insertions(+), 20 deletions(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index f24bf49be0..f5e678e997 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -2255,6 +2255,23 @@ static nodemask_t *policy_mbind_nodemask(gfp_t gfp)
>  	return NULL;
>  }
>  
> +static unsigned int allowed_mems_nr(struct hstate *h)
> +{
> +	int node;
> +	unsigned int nr = 0;
> +	nodemask_t *mbind_nodemask;
> +	unsigned int *array = h->free_huge_pages_node;
> +	gfp_t gfp_mask = htlb_alloc_mask(h);
> +
> +	mbind_nodemask = policy_mbind_nodemask(gfp_mask);
> +	for_each_node_mask(node, cpuset_current_mems_allowed) {
> +		if (!mbind_nodemask || node_isset(node, *mbind_nodemask))
> +			nr += array[node];
> +	}
> +
> +	return nr;
> +}
> +
>  /*
>   * Increase the hugetlb pool such that it can accommodate a reservation
>   * of size 'delta'.
> @@ -2277,7 +2294,8 @@ static int gather_surplus_pages(struct hstate *h, long delta)
>  		alloc_nodemask = cpuset_current_mems_allowed;
>  
>  	lockdep_assert_held(&hugetlb_lock);
> -	needed = (h->resv_huge_pages + delta) - h->free_huge_pages;
> +	needed = max_t(long, (delta - allowed_mems_nr(h)),
> +			((h->resv_huge_pages + delta) - h->free_huge_pages));
>  	if (needed <= 0) {
>  		h->resv_huge_pages += delta;
>  		return 0;
> @@ -2311,8 +2329,9 @@ static int gather_surplus_pages(struct hstate *h, long delta)
>  	 * because either resv_huge_pages or free_huge_pages may have changed.
>  	 */
>  	spin_lock_irq(&hugetlb_lock);
> -	needed = (h->resv_huge_pages + delta) -
> -			(h->free_huge_pages + allocated);
> +	needed = max_t(long, ((delta - allowed_mems_nr(h)) - allocated),
> +			((h->resv_huge_pages + delta) -
> +				(h->free_huge_pages + allocated)));
>  	if (needed > 0) {
>  		if (alloc_ok)
>  			goto retry;
> @@ -4513,23 +4532,6 @@ static int __init hugepage_alloc_threads_setup(char *s)
>  }
>  __setup("hugepage_alloc_threads=", hugepage_alloc_threads_setup);
>  
> -static unsigned int allowed_mems_nr(struct hstate *h)
> -{
> -	int node;
> -	unsigned int nr = 0;
> -	nodemask_t *mbind_nodemask;
> -	unsigned int *array = h->free_huge_pages_node;
> -	gfp_t gfp_mask = htlb_alloc_mask(h);
> -
> -	mbind_nodemask = policy_mbind_nodemask(gfp_mask);
> -	for_each_node_mask(node, cpuset_current_mems_allowed) {
> -		if (!mbind_nodemask || node_isset(node, *mbind_nodemask))
> -			nr += array[node];
> -	}
> -
> -	return nr;
> -}
> -
>  void hugetlb_report_meminfo(struct seq_file *m)
>  {
>  	struct hstate *h;
> -- 
> 2.55.0