linux-kernel - Re: [PATCH 00/40] Memory allocation profiling

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Message-ID: <ZFkb1p80vq19rieI@moria.home.lan>
Date:   Mon, 8 May 2023 11:57:10 -0400
From:   Kent Overstreet <kent.overstreet@...ux.dev>
To:     Petr Tesařík <petr@...arici.cz>
Cc:     Michal Hocko <mhocko@...e.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
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Subject: Re: [PATCH 00/40] Memory allocation profiling

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@...ux.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.