Arnd BergmannJul 23, 2024

I had a feeling that kernel compilation got slower recently and tried to find the slowest file across randconfig builds. It turned out to be arch/x86/xen/setup.c, which takes 15 seconds to preprocess on a reasonably fast Apple M1 Ultra.

This all comes from one line "extra_pages = min3(EXTRA_MEM_RATIO * min(max_pfn, PFN_DOWN(MAXMEM)), extra_pages, max_pages - max_pfn);" that expands to 47MB of preprocessor output after commits 80fcac55385c..867046cc70277.

Show threadljsJul 23, 2024
@arnd we going to revert that series then?

I feel there is pedantry at play...
Show threadOmar SandovalJul 23, 2024
@ljs @arnd eh I don't think it's fair to call this pedantry. This looks like a legitimate quality of life improvement for a common annoyance with min/max, but given the consequences, it's fair to say that it's not worth it.
Show threadljsJul 23, 2024
@osandov @arnd Regardless, this is an unacceptable build regression.

Chatted to @arnd on IRC who suggests he is tied up with stuff to dig into this more so I'll have a wee look :)

EDIT: Think that'll be more likely a report to list + leave others to solve as this seems quite involved and I have a ton of things to do :>)
Show threadljs
@osandov @arnd For those following, posted https://lore.kernel.org/linux-mm/[email protected]/T/#u summarising situation + showing some results on my local box (ignore cringe hostname of said box)
Build performance regressions originating from min()/max() macros

Jul 23, 2024 at 10:08pmWeb