Re: [PATCH] mm: hugetlb: Add Kconfig option to set default nr_overcommit_hugepages

[David Rientjes]

On Fri, 9 Jun 2023, Josh Triplett wrote:

> The default kernel configuration does not allow any huge page allocation
> until after setting nr_hugepages or nr_overcommit_hugepages to a
> non-zero value; without setting those, mmap attempts with MAP_HUGETLB
> will always fail with -ENOMEM. nr_overcommit_hugepages allows userspace
> to attempt to allocate huge pages at runtime, succeeding if the kernel
> can find or assemble a free huge page.
> 
> Provide a Kconfig option to make nr_overcommit_hugepages default to
> unlimited, which permits userspace to always attempt huge page
> allocation on a best-effort basis. This makes it easier and more
> worthwhile for random applications and libraries to opportunistically
> attempt MAP_HUGETLB allocations without special configuration.
> 
> In particular, current versions of liburing with IORING_SETUP_NO_MMAP
> attempt to allocate the rings in a huge page. This seems likely to lead
> to more applications and libraries attempting to use huge pages.
> 
> Signed-off-by: Josh Triplett <josh@xxxxxxxxxxxxxxxx>

Why not do this in an initscript?

Or, if absolutely necessary, a kernel command line parameter?

A Kconfig option to set a default value to be ULONG_MAX seems strange if 
you can just write the value to procfs.