On 5/3/21 1:07 PM, Peter Krempa wrote:
On Fri, Apr 23, 2021 at 15:24:23 +0200, Michal Privoznik wrote:
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@redhat.com> --- 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..89b31af3ca 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; /* in kibibytes */ +static virOnceControl virHostMemGetTHPSizeOnce = VIR_ONCE_CONTROL_INITIALIZER;
#ifdef __FreeBSD__ # define BSD_MEMORY_STATS_ALL 4 @@ -920,3 +923,63 @@ virHostMemAllocPages(unsigned int npages,
return ncounts; } + +#if defined(__linux__) +# define HPAGE_PMD_SIZE_PATH "/sys/kernel/mm/transparent_hugepage/hpage_pmd_size" +static int
Nothing checks the return value.
+virHostMemGetTHPSizeSysfs(unsigned long long *size) +{ + g_autofree char *buf = NULL; + + /* 1KiB limit is more than enough. */ + if (virFileReadAll(HPAGE_PMD_SIZE_PATH, 1024, &buf) < 0) + return -1; + + virStringTrimOptionalNewline(buf); + if (virStrToLong_ull(buf, NULL, 10, size) < 0) { + virReportError(VIR_ERR_INTERNAL_ERROR, + _("unable to parse THP PMD size: %s"), buf); + return -1; + } + + /* Size is now in bytes. Convert to KiB. */ + *size >>= 10; + return 0; +} +#endif /* defined(__linux__) */ + + +static void +virHostMemGetTHPSizeOnceInit(void) +{ +#if defined(__linux__) + virHostMemGetTHPSizeSysfs(&virHostTHPPMDSize); +#else /* !defined(__linux__) */ + VIR_WARN("Getting THP size not ported yet"); +#endif /* !defined(__linux__) */ +} + + +/** + * virHostMemGetTHPSize: + * @size: returned size of THP in kibibytes + * + * Obtain Transparent Huge Page size in kibibytes. The size + * depends on host architecture and kernel. Because of virOnce(), + * do not rely on errno in case of failure. + * + * Returns: 0 on success, + * -1 on failure. + */ +int +virHostMemGetTHPSize(unsigned long long *size) +{ + if (virOnce(&virHostMemGetTHPSizeOnce, virHostMemGetTHPSizeOnceInit) < 0)
This directly returns the return value from 'pthread_once' whose manual entry states:
RETURN VALUE Upon successful completion, pthread_once() shall return zero; otherwise, an error number shall be returned to indicate the error.
Which reads as if 'errno' is returned by the function which would make the '< 0' check wrong.
Interesting, never though about this. Just blindly copied what we have elsewhere. Looking into glibc - pthread_once will never return anything else than 0. Then uclibc-ng doesn't provide pthread_once and musl also always returns 0. I'll send a patch that fixes this issue shortly. Michal