Suren Baghdasaryan <surenb@xxxxxxxxxx> writes: > 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. > > From the changelog description I was under impression that it's vice > versa, for global OOMs you would not block (wait_on_oom_lock=false), > for memcg ones you would (wait_on_oom_lock=true). Good catch, fixed. > >> + * >> + * Returns 1 if the forward progress was achieved and some memory was freed. >> + * Returns a negative value if an error has been occurred. > > s/has been occurred/has occurred or occured Same here. Thanks!
