On Mon Jul 27, 2026 at 2:24 AM EDT, Jiayuan Chen wrote: > bpf_map_alloc_pages() picks the allocator via can_alloc_pages(), a > conservative guess for BPF program context that is always false under > PREEMPT_RT. So even a caller that really is sleepable gets the > non-blocking allocator, which never reclaims and never engages the OOM > machinery. > > Add bpf_map_alloc_page_sleepable() for callers that know they are > sleepable. The next patch uses it from the arena page fault handler. > > Signed-off-by: Jiayuan Chen <[email protected]>
Reviewed-by: Emil Tsalapatis <[email protected]> > --- > include/linux/bpf.h | 1 + > kernel/bpf/syscall.c | 21 +++++++++++++++++---- > 2 files changed, 18 insertions(+), 4 deletions(-) > > diff --git a/include/linux/bpf.h b/include/linux/bpf.h > index d9542127dfdf..9ba03622709b 100644 > --- a/include/linux/bpf.h > +++ b/include/linux/bpf.h > @@ -2779,6 +2779,7 @@ struct bpf_prog *bpf_prog_get_curr_or_next(u32 *id); > > int bpf_map_alloc_pages(const struct bpf_map *map, int nid, > unsigned long nr_pages, struct page **page_array); > +struct page *bpf_map_alloc_page_sleepable(const struct bpf_map *map, int > nid); > #ifdef CONFIG_MEMCG > void bpf_map_memcg_enter(const struct bpf_map *map, struct mem_cgroup > **old_memcg, > struct mem_cgroup **new_memcg); > diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c > index 0ff9e3aa293d..cec88450e4ce 100644 > --- a/kernel/bpf/syscall.c > +++ b/kernel/bpf/syscall.c > @@ -602,15 +602,14 @@ static bool can_alloc_pages(void) > !IS_ENABLED(CONFIG_PREEMPT_RT); > } > > +#define BPF_PAGE_GFP (GFP_KERNEL | __GFP_ZERO | __GFP_ACCOUNT | __GFP_NOWARN) > + > static struct page *__bpf_alloc_page(int nid) > { > if (!can_alloc_pages()) > return alloc_pages_nolock(__GFP_ACCOUNT, nid, 0); > > - return alloc_pages_node(nid, > - GFP_KERNEL | __GFP_ZERO | __GFP_ACCOUNT > - | __GFP_NOWARN, > - 0); > + return alloc_pages_node(nid, BPF_PAGE_GFP, 0); > } > > int bpf_map_alloc_pages(const struct bpf_map *map, int nid, > @@ -636,6 +635,20 @@ int bpf_map_alloc_pages(const struct bpf_map *map, int > nid, > return ret; > } > > +/* > + * For callers that know they run in a sleepable context, e.g. a user page > + * fault handler. can_alloc_pages() is a conservative guess made for BPF > + * program context - notably it is always false on PREEMPT_RT - so going > + * through bpf_map_alloc_pages() there would needlessly pick the > + * non-blocking allocator, which never reclaims and never engages the OOM > + * machinery. > + */ > +struct page *bpf_map_alloc_page_sleepable(const struct bpf_map *map, int nid) > +{ > + might_sleep(); > + return alloc_pages_node(nid, BPF_PAGE_GFP, 0); > +} > + > > static int btf_field_cmp(const void *a, const void *b) > {
