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

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Message-ID: <wdj72247rptlp4g7dzpvgrt3aupbvinskx3abxnhrxh32bmxvt@pm3d3k6rn7pm>
Date: Thu, 15 Feb 2024 20:00:44 -0500
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Suren Baghdasaryan <surenb@...gle.com>, mhocko@...e.com, 
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Subject: Re: [PATCH v3 13/35] lib: add allocation tagging support for memory
 allocation profiling

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@...gle.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'm just optimizing for the most common use case. I doubt there's going
to be nearly as much consumption by tools, and I'm ok with making them
do the conversion back to bytes if they really need it.