Re: [PATCH v2 01/13] virhostmem: Introduce virHostMemGetTHPSize()

New virHostMemGetTHPSize() is introduced which allows caller to obtain THP PMD (Page Middle Directory) size, which is equal to the minimal size that THP can use, taken from kernel doc (Documentation/admin-guide/mm/transhuge.rst): Some userspace (such as a test program, or an optimized memory allocation library) may want to know the size (in bytes) of a transparent hugepage:: cat /sys/kernel/mm/transparent_hugepage/hpage_pmd_size Since this size depends on the host architecture and the kernel it won't change whilst libvirtd is running. Therefore, we can use virOnce() and cache the value. Of course, we can be running under kernel that has THP disabled or has no notion of THP at all. In that case a negative value is returned to signal error. Signed-off-by: Michal Privoznik <mprivozn(a)redhat.com&gt; --- src/libvirt_private.syms | 1 + src/util/virhostmem.c | 63 ++++++++++++++++++++++++++++++++++++++++ src/util/virhostmem.h | 3 ++ tests/domaincapsmock.c | 9 ++++++ 4 files changed, 76 insertions(+)

diff --git a/src/util/virhostmem.c b/src/util/virhostmem.c index ae42978ed2..ef7b97806f 100644 --- a/src/util/virhostmem.c +++ b/src/util/virhostmem.c @@ -45,11 +45,14 @@ #include "virstring.h" #include "virnuma.h" #include "virlog.h" +#include "virthread.h" #define VIR_FROM_THIS VIR_FROM_NONE VIR_LOG_INIT("util.hostmem"); +static unsigned long long virHostTHPPMDSize;

+static virOnceControl virHostMemGetTHPSizeOnce = VIR_ONCE_CONTROL_INITIALIZER;