Re: [PATCH] mm: kfence: print the age time for alloacted objectes to trace memleak

[Marco Elver <elver@google.com>]

On Sun, 4 Aug 2024 at 05:46, chenqiwu <qiwuchen55@gmail.com> wrote:
[...]
> > I've found myself trying to figure out the elapsed time since the
> > allocation or free, based on the current timestamp.
> >
> > So something that would be more helpful is if you just change the
> > printed line for all alloc and free stack infos to say something like:
> >
> >     seq_con_printf(seq, "%s by task %d on cpu %d at %lu.%06lus (%lu.%06lus ago):\n",
> >
> > So rather than saying this info is the "age", we just say the elapsed
> > time. That generalizes this bit of info, and it'll be available for
> > both alloc and free stacks.
> >
> > Does that work for you?
> >
> It does not work for me actually, since it's unintuitive to figure out memory leaks

The number printed is the same. It's just the change of "age" to "ago".

> by the elapsed time of allocated stacks when inspect /sys/kernel/debug/kfence/objects.
> It's unnecessary to print the elapsed time of allocated stacks for the objects in KFENCE_OBJECT_FREED
> state. For the elapsed time of free stacks, it seems no available scenarion currently.
> BTW, The change from "age" to "ago" is okay to me!

Well, what I'm saying, having this info also for FREED objects on the
free stack can be useful in some debugging scenarios when you get a
use-after-free, and you want to know the elapsed time since the free
happened. I have done this calculation manually before, which is why I
suggested it. Maybe it's not useful for you for finding leaks, but
that's just one usecase.

Thanks,
-- Marco