On Fri Jul 17, 2026 at 7:37 AM EDT, Jiayuan Chen wrote: > arena is the only map type whose map_mem_usage() still returns 0, so > "bpftool map show" and fdinfo always showed 0 memlock for an arena no > matter how many pages it had. > > Count the pages that are actually mapped into the arena: bump a counter in > apply_range_set_cb() when a page goes in and drop it in > apply_range_clear_cb() when a page goes out, both under the arena spinlock. > map_mem_usage() then just returns nr_pages << PAGE_SHIFT. > > Only real data pages are counted, not the scratch page. > > Signed-off-by: Jiayuan Chen <[email protected]>
Reviewed-by: Emil Tsalapatis <[email protected]> > > --- > To sashiko: > 1. __bpf_alloc_page::can_alloc_pages already check whether we are under lock. > 2. apply_to_page_range() does not allocate page tables here. > arena_map_alloc() already did it. > --- > kernel/bpf/arena.c | 10 ++++++++-- > 1 file changed, 8 insertions(+), 2 deletions(-) > > diff --git a/kernel/bpf/arena.c b/kernel/bpf/arena.c > index 8dbc24460890..f046e878f7ae 100644 > --- a/kernel/bpf/arena.c > +++ b/kernel/bpf/arena.c > @@ -55,8 +55,10 @@ struct bpf_arena { > struct vm_struct *kern_vm; > struct page *scratch_page; > struct range_tree rt; > - /* protects rt */ > + /* protects rt and nr_pages */ > rqspinlock_t spinlock; > + /* number of pages currently populated in the arena */ > + u64 nr_pages; > struct list_head vma_list; > /* protects vma_list */ > struct mutex lock; > @@ -196,6 +198,7 @@ static int apply_range_set_cb(pte_t *pte, unsigned long > addr, void *data) > set_pte_at(&init_mm, addr, pte, pteval); > #endif > d->i++; > + WRITE_ONCE(d->arena->nr_pages, d->arena->nr_pages + 1); > return 0; > } > > @@ -231,6 +234,7 @@ static int apply_range_clear_cb(pte_t *pte, unsigned long > addr, void *data) > return 0; > > __llist_add(&page->pcp_llist, d->free_pages); > + WRITE_ONCE(d->arena->nr_pages, d->arena->nr_pages - 1); > return 0; > } > > @@ -413,7 +417,9 @@ static int arena_map_check_btf(struct bpf_map *map, const > struct btf *btf, > > static u64 arena_map_mem_usage(const struct bpf_map *map) > { > - return 0; > + struct bpf_arena *arena = container_of(map, struct bpf_arena, map); > + > + return (u64)READ_ONCE(arena->nr_pages) << PAGE_SHIFT; > } > > struct vma_list {
