Re: [RFC] should physmem be cgroup-aware?

On 2026-08-20 Pádraig Brady wrote:
> Re syscall overhead, it's unfortunate, but I don't see a way around
> that at present.

The syscall count in get_cgroup2_cpu_quota could be reduced by 25 % by
avoiding stdio. With glibc, fopen + getline + fclose is four syscalls:
openat + fstat + read + close. Using open + read + close would need only
three.

> I do note that sort(1) uses both nproc() and physmem_total(), which
> suggests a shared or cached interface may be useful, but that can
> come at a later stage.

One could cache the mount point and the cgroup path from
/proc/self/cgroup. It would typically save 4-5 syscalls. I don't know
if it's worth the extra code.

"sort /dev/null" (coreutils 9.11) makes over 40 rt_sigaction syscalls,
so in sort(1) the cgroup related syscalls aren't so large portion of
the total syscall count.

-- 
Lasse Collin