| Message ID | 88fc41edeb5667534cde344c9220fcdfc00047b1.1686359973.git.josh@joshtriplett.org (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm: hugetlb: Add Kconfig option to set default nr_overcommit_hugepages | expand |
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@joshtriplett.org> 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.
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@joshtriplett.org> > > 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 ...
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@joshtriplett.org> > > > > 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.
diff --git a/mm/Kconfig b/mm/Kconfig index 7672a22647b4..32c13610c5c4 100644 --- a/mm/Kconfig +++ b/mm/Kconfig @@ -824,6 +824,20 @@ config READ_ONLY_THP_FOR_FS endif # TRANSPARENT_HUGEPAGE +config HUGEPAGE_OVERCOMMIT_DEFAULT_UNLIMITED + bool "Allow huge page allocation attempts by default" + depends on HUGETLB_PAGE + help + By default, the kernel does not allow any huge page allocation until + after setting nr_hugepages or nr_overcommit_hugepages to a non-zero + value. 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. + + Enable this option to make nr_overcommit_hugepages default to + unlimited, which permits userspace to always attempt hugepage + allocation. + # # UP and nommu archs use km based percpu allocator # diff --git a/mm/hugetlb.c b/mm/hugetlb.c index f154019e6b84..65abbe254e10 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -4305,6 +4305,8 @@ void __init hugetlb_add_hstate(unsigned int order) mutex_init(&h->resize_lock); h->order = order; h->mask = ~(huge_page_size(h) - 1); + if (IS_ENABLED(CONFIG_HUGEPAGE_OVERCOMMIT_DEFAULT_UNLIMITED)) + h->nr_overcommit_huge_pages = ULONG_MAX; for (i = 0; i < MAX_NUMNODES; ++i) INIT_LIST_HEAD(&h->hugepage_freelists[i]); INIT_LIST_HEAD(&h->hugepage_activelist);
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@joshtriplett.org> --- mm/Kconfig | 14 ++++++++++++++ mm/hugetlb.c | 2 ++ 2 files changed, 16 insertions(+)