On Mon, Aug 18, 2025 at 10:02 AM Roman Gushchin <roman.gushchin@xxxxxxxxx> wrote: > > Introduce bpf_out_of_memory() bpf kfunc, which allows to declare > an out of memory events and trigger the corresponding kernel OOM > handling mechanism. > > It takes a trusted memcg pointer (or NULL for system-wide OOMs) > as an argument, as well as the page order. > > If the wait_on_oom_lock argument is not set, only one OOM can be > declared and handled in the system at once, so if the function is > called in parallel to another OOM handling, it bails out with -EBUSY. > This mode is suited for global OOM's: any concurrent OOMs will likely > do the job and release some memory. In a blocking mode (which is > suited for memcg OOMs) the execution will wait on the oom_lock mutex. > > The function is declared as sleepable. It guarantees that it won't > be called from an atomic context. It's required by the OOM handling > code, which is not guaranteed to work in a non-blocking context. > > Handling of a memcg OOM almost always requires taking of the > css_set_lock spinlock. The fact that bpf_out_of_memory() is sleepable > also guarantees that it can't be called with acquired css_set_lock, > so the kernel can't deadlock on it. > > Signed-off-by: Roman Gushchin <roman.gushchin@xxxxxxxxx> > --- > mm/oom_kill.c | 45 +++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 45 insertions(+) > > diff --git a/mm/oom_kill.c b/mm/oom_kill.c > index 25fc5e744e27..df409f0fac45 100644 > --- a/mm/oom_kill.c > +++ b/mm/oom_kill.c > @@ -1324,10 +1324,55 @@ __bpf_kfunc int bpf_oom_kill_process(struct oom_control *oc, > return 0; > } > > +/** > + * bpf_out_of_memory - declare Out Of Memory state and invoke OOM killer > + * @memcg__nullable: memcg or NULL for system-wide OOMs > + * @order: order of page which wasn't allocated > + * @wait_on_oom_lock: if true, block on oom_lock > + * @constraint_text__nullable: custom constraint description for the OOM report > + * > + * Declares the Out Of Memory state and invokes the OOM killer. > + * > + * OOM handlers are synchronized using the oom_lock mutex. If wait_on_oom_lock > + * is true, the function will wait on it. Otherwise it bails out with -EBUSY > + * if oom_lock is contended. > + * > + * Generally it's advised to pass wait_on_oom_lock=true for global OOMs > + * and wait_on_oom_lock=false for memcg-scoped OOMs.
