Re: [PATCH v3 13/35] lib: add allocation tagging support for memory allocation profiling

Kent Overstreet
2024-02-16T01:27:45Z

On Thu, Feb 15, 2024 at 08:22:44PM -0500, Pasha Tatashin wrote:
> On Thu, Feb 15, 2024 at 8:00 PM Kent Overstreet
> <kent.overstreet@linux.dev> wrote:
> >
> > On Thu, Feb 15, 2024 at 04:54:38PM -0800, Andrew Morton wrote:
> > > On Mon, 12 Feb 2024 13:38:59 -0800 Suren Baghdasaryan <surenb@google.com> wrote:
> > >
> > > > +Example output.
> > > > +
> > > > +::
> > > > +
> > > > + > cat /proc/allocinfo
> > > > +
> > > > + 153MiB mm/slub.c:1826 module:slub func:alloc_slab_page
> > > > + 6.08MiB mm/slab_common.c:950 module:slab_common func:_kmalloc_order
> > > > + 5.09MiB mm/memcontrol.c:2814 module:memcontrol func:alloc_slab_obj_exts
> > > > + 4.54MiB mm/page_alloc.c:5777 module:page_alloc func:alloc_pages_exact
> > > > + 1.32MiB include/asm-generic/pgalloc.h:63 module:pgtable func:__pte_alloc_one
> > >
> > > I don't really like the fancy MiB stuff. Wouldn't it be better to just
> > > present the amount of memory in plain old bytes, so people can use sort
> > > -n on it?
> >
> > They can use sort -h on it; the string_get_size() patch was specifically
> > so that we could make the output compatible with sort -h
> >
> > > And it's easier to tell big-from-small at a glance because
> > > big has more digits.
> > >
> > > Also, the first thing any sort of downstream processing of this data is
> > > going to have to do is to convert the fancified output back into
> > > plain-old-bytes. So why not just emit plain-old-bytes?
> > >
> > > If someone wants the fancy output (and nobody does) then that can be
> > > done in userspace.
> >
> > I like simpler, more discoverable tools; e.g. we've got a bunch of
> > interesting stuff in scripts/ but it doesn't get used nearly as much -
> > not as accessible as cat'ing a file, definitely not going to be
> > installed by default.
>
> I also prefer plain bytes instead of MiB. A driver developer that
> wants to verify up-to the byte allocations for a new data structure
> that they added is going to be disappointed by the rounded MiB
> numbers.

That's a fair point.

> The data contained in this file is not consumable without at least
> "sort -h -r", so why not just output bytes instead?
>
> There is /proc/slabinfo and there is a slabtop tool.
> For raw /proc/allocinfo we can create an alloctop tool that would
> parse, sort and show data in human readable format based on various
> criteria.
>
> We should also add at the top of this file "allocinfo - version: 1.0",
> to allow future extensions (i.e. column for proc name).

How would we feel about exposing two different versions in /proc? It
should be a pretty minimal addition to .text.

Personally, I hate trying to count long strings digits by eyeball...