Re: [PATCH] alloc_tag: introduce Kconfig option for default compressed profiling

[Shakeel Butt <shakeel.butt@linux.dev>]

On Wed, Apr 16, 2025 at 02:08:31PM -0700, Suren Baghdasaryan wrote:
> On Wed, Apr 16, 2025 at 11:06 AM Usama Arif <usamaarif642@gmail.com> wrote:
> >
> > With this Kconfig option enabled, the kernel stores allocation tag references
> > in the page flags by default.
> >
> > There are 2 reasons to introduce this:
> > - As mentioned in [1], compressed tags dont have system memory overhead
> > and much lower performance overhead. It would be preferrable to have this as
> > the default option, and to be able to switch it at compile time. Another
> > option is to just declare the static key as true by default?
> > - As compressed option is the best one, it doesn't make sense to have to
> > change both defconfig and command line options to enable memory
> > allocation profiling. Changing commandline across a large number of services
> > can result in signifcant work, which shouldn't be needed if the kernel
> > defconfig needs to be changed anyways.
> 
> The reason tag compression is not the default option is because it
> works only if there are enough free bits in the page flags to store a
> tag index. If you configure it to use page flags and your build does
> not have enough free bits, the profiling will be disabled (see
> alloc_tag_sec_init()).

Is it possible to fail the build in that case i.e. check the page flags
availability at build time?