Re: [PATCH 00/40] Memory allocation profiling

Kent Overstreet
2023-05-08T15:57:33Z

On Mon, May 08, 2023 at 05:52:06PM +0200, Petr Tesařík wrote:
> On Sun, 7 May 2023 13:20:55 -0400
> Kent Overstreet <kent.overstreet@linux.dev> wrote:
>
> > On Thu, May 04, 2023 at 11:07:22AM +0200, Michal Hocko wrote:
> > > No. I am mostly concerned about the _maintenance_ overhead. For the
> > > bare tracking (without profiling and thus stack traces) only those
> > > allocations that are directly inlined into the consumer are really
> > > of any use. That increases the code impact of the tracing because any
> > > relevant allocation location has to go through the micro surgery.
> > >
> > > e.g. is it really interesting to know that there is a likely memory
> > > leak in seq_file proper doing and allocation? No as it is the specific
> > > implementation using seq_file that is leaking most likely. There are
> > > other examples like that See?
> >
> > So this is a rather strange usage of "maintenance overhead" :)
> >
> > But it's something we thought of. If we had to plumb around a _RET_IP_
> > parameter, or a codetag pointer, it would be a hassle annotating the
> > correct callsite.
> >
> > Instead, alloc_hooks() wraps a memory allocation function and stashes a
> > pointer to a codetag in task_struct for use by the core slub/buddy
> > allocator code.
> >
> > That means that in your example, to move tracking to a given seq_file
> > function, we just:
> > - hook the seq_file function with alloc_hooks
>
> Thank you. That's exactly what I was trying to point out. So you hook
> seq_buf_alloc(), just to find out it's called from traverse(), which
> is not very helpful either. So, you hook traverse(), which sounds quite
> generic. Yes, you're lucky, because it is a static function, and the
> identifier is not actually used anywhere else (right now), but each
> time you want to hook something, you must make sure it does not
> conflict with any other identifier in the kernel...

Cscope makes quick and easy work of this kind of stuff.