Re: [PATCH] setup: dynamically detect default huge page size

[Prateek <kprateek283@gmail.com>]

Hi Gabriel,

Thanks for the review.

On Mon, Jun 22, 2026 at 16:49 Gabriel Krisman Bertazi wrote:
> > +static size_t get_huge_page_size(void)
> > +{
> > +   static size_t hps;
>
> Please, initialize your static variables to makes it readable. I.e,
> should be initialized it to 2MB.

hps is left at 0 on purpose as a "not computed yet" flag -- same thing get_page_size() does in arch/aarch64/lib.h with cache_val. If I set hps = 2MB upfront, the first call just returns 2MB without ever reading /proc/meminfo, which defeats the point.

> > +   size_t ret = 2 * 1024 * 1024; /* fallback: 2MB */
>
> ret redundant with hps, could go away.

The local ret is there so I only write to hps once at the end. If two threads race into this function, neither one sees a half-baked fallback value in hps. The race itself is harmless since both threads would compute the same result anyway.

> > +       if (p + 13 <= end &&
> > +           p[0]  == 'H' && p[1]  == 'u' && p[2]  == 'g' &&
> > +           p[3]  == 'e' && p[4]  == 'p' && p[5]  == 'a' &&
> > +           p[6]  == 'g' && p[7]  == 'e' && p[8]  == 's' &&
> > +           p[9]  == 'i' && p[10] == 'z' && p[11] == 'e' &&
> > +           p[12] == ':') {
>
> This is unreadable.  It would be much better as a two line loop
> iterating over two strings...  But then, why not create it a couple line
> implementation of memcmp and atoi in arch/generic/lib.h instead?

Yeah, the char-by-char match is ugly, agreed. For v2 I'll add a __uring_memcmp in nolibc.c and shim it in lib.h behind #ifdef CONFIG_NOLIBC, same way memset/malloc/free are done today. arch/generic/lib.h only gets included on archs without nolibc support, so putting memcmp there wouldn't help x86/aarch64/riscv64 nolibc builds. nolibc.c + lib.h shim covers all configs. Then setup.c just calls memcmp(p, "Hugepagesize:", 13) -- normal builds use libc's memcmp, nolibc builds use the shim. I'll keep the digit parsing loop as-is since it's simple enough and pulling in atoi feels like overkill.

> This function should go in arch/generic/lib.h too.  A hint is the
> get_page_size is already there.

get_huge_page_size() only lives in setup.c and uses the __sys* wrappers from syscall.h, which work in all build configs. Unlike get_page_size() which is needed across multiple files, there's no reason to put this in the arch headers and duplicate it four times.

> That said, we should be looking into something like the kernel's nolibc
> instead of reinventing libc.

Agreed, worth looking into separately. This patch just fixes the immediate hugepage issue.

Will send a v2 with the memcmp approach.

Thanks,
Prateek