On Tue, Feb 11, 2025 at 3:59 PM Stephen Brennan <stephen.s.brennan@xxxxxxxxxx> wrote: > > Alexei Starovoitov <alexei.starovoitov@xxxxxxxxx> writes: > > On Thu, Feb 6, 2025 at 5:21 PM Stephen Brennan > > <stephen.s.brennan@xxxxxxxxxx> wrote: > >> When the feature was implemented in pahole, my measurements indicated > >> that vmlinux BTF size increased by about 25.8%, and module BTF size > >> increased by 53.2%. Due to these increases, the feature is implemented > >> behind a new config option, allowing users sensitive to increased memory > >> usage to disable it. > >> > > > > ... > >> +config DEBUG_INFO_BTF_GLOBAL_VARS > >> + bool "Generate BTF type information for all global variables" > >> + default y > >> + depends on DEBUG_INFO_BTF && PAHOLE_VERSION >= 128 > >> + help > >> + Include type information for all global variables in the BTF. This > >> + increases the size of the BTF information, which increases memory > >> + usage at runtime. With global variable types available, runtime > >> + debugging and tracers may be able to provide more detail. > > > > This is not a solution. > > Even if it's changed to 'default n' distros will enable it > > like they enable everything and will suffer a regression. > > > > We need to add a new module like vmlinux_btf.ko that will contain > > this additional BTF data. For global vars and everything else we might need. > > Fair enough. I believe I had shared Alan Maguire's proof-of-concept for > that idea a while back for an older version of this feature: > > https://lore.kernel.org/all/20221104231103.752040-10-stephen.s.brennan@xxxxxxxxxx/ Right vmlinux_extra was discussed in various context, so let's make it happen. > We can dust that off and include it for a new version of this series. > I'd be curious of what you'd like to see for kernel modules? A > three-level tree would be too complex, in my opinion. What is the use case for vars in kernel modules? > module BTF size increased by 53.2%. This is the sum of all mods with vars divided by the sum of all mods without? Any outliers there? I would expect modules to have few global variables. So before we decide on what to do with vars in mods lets figure out the need.
