Re: [RFC PATCH 00/30] Code tagging framework and applications

Suren Baghdasaryan
2022-09-01T05:05:51Z

On Wed, Aug 31, 2022 at 9:52 PM Oscar Salvador <osalvador@suse.de> wrote:
>
> On Tue, Aug 30, 2022 at 02:48:49PM -0700, Suren Baghdasaryan wrote:
> > ===========================
> > Code tagging framework
> > ===========================
> > Code tag is a structure identifying a specific location in the source code
> > which is generated at compile time and can be embedded in an application-
> > specific structure. Several applications of code tagging are included in
> > this RFC, such as memory allocation tracking, dynamic fault injection,
> > latency tracking and improved error code reporting.
> > Basically, it takes the old trick of "define a special elf section for
> > objects of a given type so that we can iterate over them at runtime" and
> > creates a proper library for it.
> >
> > ===========================
> > Memory allocation tracking
> > ===========================
> > The goal for using codetags for memory allocation tracking is to minimize
> > performance and memory overhead. By recording only the call count and
> > allocation size, the required operations are kept at the minimum while
> > collecting statistics for every allocation in the codebase. With that
> > information, if users are interested in mode detailed context for a
> > specific allocation, they can enable more in-depth context tracking,
> > which includes capturing the pid, tgid, task name, allocation size,
> > timestamp and call stack for every allocation at the specified code
> > location.
> > Memory allocation tracking is implemented in two parts:
> >
> > part1: instruments page and slab allocators to record call count and total
> > memory allocated at every allocation in the source code. Every time an
> > allocation is performed by an instrumented allocator, the codetag at that
> > location increments its call and size counters. Every time the memory is
> > freed these counters are decremented. To decrement the counters upon free,
> > allocated object needs a reference to its codetag. Page allocators use
> > page_ext to record this reference while slab allocators use memcg_data of
> > the slab page.
> > The data is exposed to the user space via a read-only debugfs file called
> > alloc_tags.
>
> Hi Suren,
>
> I just posted a patch [1] and reading through your changelog and seeing your PoC,
> I think we have some kind of overlap.
> My patchset aims to give you the stacktrace <-> relationship information and it is
> achieved by a little amount of extra code mostly in page_owner.c/ and lib/stackdepot.
>
> Of course, your works seems to be more complete wrt. the information you get.
>
> I CCed you in case you want to have a look
>
> [1] https://lkml.org/lkml/2022/9/1/36

Hi Oscar,
Thanks for the note. I'll take a look most likely on Friday and will
follow up with you.
Thanks,
Suren.

>
> Thanks
>
>
> --
> Oscar Salvador
> SUSE Labs