Re: [PATCH v9.1] mm/damon: add node_eligible_mem_bp goal metric

[SeongJae Park <sj@kernel.org>]

On Sun, 26 Apr 2026 18:02:09 -0700 Ravi Jonnalagadda <ravis.opensrc@gmail.com> wrote:
[...]
> +static phys_addr_t damos_calc_eligible_bytes(struct damon_ctx *c,
> +		struct damos *s, int nid, phys_addr_t *total)
> +{
> +	struct damon_target *t;
> +	struct damon_region *r;
> +	phys_addr_t total_eligible = 0;
> +	phys_addr_t node_eligible = 0;
> +
> +	damon_for_each_target(t, c) {
> +		damon_for_each_region(r, t) {
> +			phys_addr_t addr, end_addr;
> +
> +			if (!__damos_valid_target(r, s))
> +				continue;
> +
> +			/* Convert from core address units to physical bytes */
> +			addr = (phys_addr_t)r->ar.start * c->addr_unit;
> +			end_addr = (phys_addr_t)r->ar.end * c->addr_unit;
> +			while (addr < end_addr) {
> +				struct folio *folio;
> +				phys_addr_t folio_start, folio_end;
> +				phys_addr_t overlap_start, overlap_end;
> +				phys_addr_t counted;
> +
> +				folio = damon_get_folio(PHYS_PFN(addr));
> +				if (!folio) {
> +					addr = PAGE_ALIGN_DOWN(addr + PAGE_SIZE);
> +					continue;
> +				}

Sashiko found this could result in an infinite loop if 'addr + PAGE_SIZE'
overflows.  The probability is quite low, but could we fix this?  Maybe like
below?

'''
--- a/mm/damon/core.c
+++ b/mm/damon/core.c
@@ -2349,7 +2349,10 @@ static phys_addr_t damos_calc_eligible_bytes(struct damon_ctx *c,

                                folio = damon_get_folio(PHYS_PFN(addr));
                                if (!folio) {
-                                       addr = PAGE_ALIGN_DOWN(addr + PAGE_SIZE);
+                                       addr = PAGE_ALIGN_DOWN(addr +
+                                                       PAGE_SIZE);
+                                       if (!addr)
+                                               break;
                                        continue;
                                }
'''

Ravi, could you please post one more version (maybe v9.2) with the abive fix if
it looks good to you?

[1] https://lore.kernel.org/20260427012429.D25C2C2BCAF@smtp.kernel.org


Thanks,
SJ

[...]