Re: [PATCH v2 12/14] mm/cma: centralize CMA pageblock initialization

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential
issue to consider:
- [Medium] mm/cma: skipped and per-PFN managed page accounting in
  cma_activate_area()
--

commit cd588f911bb59c4583e63d2e776ba252d0663161
Author: Muchun Song <muchun.song@linux.dev>

mm/cma: centralize CMA pageblock initialization

This commit moves the initialization of early-reserved CMA pageblocks from
hugetlb into cma_activate_area() and restores managed-page accounting for
those pages if CMA activation fails.

> diff --git a/mm/cma.c b/mm/cma.c
> index 9ec1d1fd5dff5..46e72734ba729 100644
> --- a/mm/cma.c
> +++ b/mm/cma.c

[ ... ]

> @@ -191,12 +195,13 @@ static void __init cma_activate_area(struct cma *cma)
>  	/* Expose all pages to the buddy, they are useless for CMA. */
>  	if (!test_bit(CMA_RESERVE_PAGES_ON_ERROR, &cma->flags)) {
>  		for (r = 0; r < cma->nranges; r++) {
> -			unsigned long start_pfn;
> -
>  			cmr = &cma->ranges[r];
> -			start_pfn = r <= allocrange ? early_pfn[r] : cmr->early_pfn;
> +			end_pfn = r <= allocrange ? early_pfn[r] : cmr->early_pfn;
> +			for (pfn = cmr->base_pfn; pfn < end_pfn; pfn++)
> +				adjust_managed_page_count(pfn_to_page(pfn), 1);
> +
>  			end_pfn = cmr->base_pfn + cmr->count;
> -			for (pfn = start_pfn; pfn < end_pfn; pfn++)
> +			for (; pfn < end_pfn; pfn++)
>  				free_reserved_page(pfn_to_page(pfn));
>  		}
>  	}

[Severity: Medium]
Does gating the adjust_managed_page_count() loop on
!CMA_RESERVE_PAGES_ON_ERROR leave early-reserved gigantic hugetlb pages
unaccounted in zone->managed_pages and totalram_pages if CMA activation
fails?

When crashkernel=...,cma is used alongside hugetlb_cma,
hugetlb_cma_add_crashkernel_ranges() sets CMA_RESERVE_PAGES_ON_ERROR on
the hugetlb_cma area before hugetlb_bootmem_alloc() reserves gigantic
pages from it via cma_reserve_early().  gather_bootmem_prealloc_node()
always skips adjust_managed_page_count() for hugetlb_early_cma(h) folios,
and those folios remain active in the hugetlb pool even if
cma_activate_area() fails, so their managed page count needs to be
restored regardless of CMA_RESERVE_PAGES_ON_ERROR.

Also, calling adjust_managed_page_count(pfn_to_page(pfn), 1) once per base
PFN invokes setup_per_zone_lowmem_reserve() for every 4 KiB page (262,144
times per 1 GiB page) instead of stepping by pageblock_nr_pages or
adjusting by end_pfn - cmr->base_pfn.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261113033442.62970-1-songmuchun@bytedance.com?part=12