mm/Kconfig | 14 ++++++++++++++ mm/hugetlb.c | 2 ++ 2 files changed, 16 insertions(+)
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(+)
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);
--
2.40.1On 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 ... -- Cheers, David / dhildenb
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. -- Mike Kravetz
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