On 11.06.23 07:20, David Rientjes wrote:
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.
Agreed, not to mention that huge pages in some environment can cause
trouble (some architectures -- or with gigantic huge pages -- don't
support huge page migration and you can run into trouble with
ZONE_MOVABLE or MIGRATE_CMA, because you'll end up "consuming" all
memory for unmovable allocations in the system), and we shouldn't
advocate the use of unlimited overcommit for huge pages ...
--
Cheers,
David / dhildenb
