malloc: Add Huge Page support for mmap

With the morecore hook removed, there is not easy way to provide huge
pages support on with glibc allocator without resorting to transparent
huge pages.  And some users and programs do prefer to use the huge pages
directly instead of THP for multiple reasons: no splitting, re-merging
by the VM, no TLB shootdowns for running processes, fast allocation
from the reserve pool, no competition with the rest of the processes
unlike THP, no swapping all, etc.

This patch extends the 'glibc.malloc.hugetlb' tunable: the value
'2' means to use huge pages directly with the system default size,
while a positive value means and specific page size that is matched
against the supported ones by the system.

Currently only memory allocated on sysmalloc() is handled, the arenas
still uses the default system page size.

To test is a new rule is added tests-malloc-hugetlb2, which run the
addes tests with the required GLIBC_TUNABLE setting.  On systems without
a reserved huge pages pool, is just stress the mmap(MAP_HUGETLB)
allocation failure.  To improve test coverage it is required to create
a pool with some allocated pages.

Checked on x86_64-linux-gnu.

Reviewed-by: DJ Delorie <dj@redhat.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/manual/tunables.texi b/manual/tunables.texi
index 9ca6e3f603..58a47b2e9b 100644
--- a/manual/tunables.texi
+++ b/manual/tunables.texi
@@ -278,6 +278,13 @@ default value is @code{0}, which disables any additional support on
 Setting its value to @code{1} enables the use of @code{madvise} with
 @code{MADV_HUGEPAGE} after memory allocation with @code{mmap}.  It is enabled
 only if the system supports Transparent Huge Page (currently only on Linux).
+
+Setting its value to @code{2} enables the use of Huge Page directly with
+@code{mmap} with the use of @code{MAP_HUGETLB} flag.  The huge page size
+to use will be the default one provided by the system.  A value larger than
+@code{2} specifies huge page size, which will be matched against the system
+supported ones.  If provided value is invalid, @code{MAP_HUGETLB} will not
+be used.
 @end deftp
 
 @node Dynamic Linking Tunables