On 06/12/23 11:12, David Hildenbrand wrote: > 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 ... > Agree with David(s). Such an option should really be decided by a sysadmin. Any reason why liburing can not use THP? Seems like that would provide the desired functionality. -- Mike Kravetz
