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util/oslib-posix: Don't create too many threads with small memory or little pages

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Let's limit the number of threads to something sane, especially that
- We don't have more threads than the number of pages we have
- We don't have threads that initialize small (< 64 MiB) memory

Reviewed-by: Pankaj Gupta <pankaj.gupta@ionos.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
Message-Id: <20211217134611.31172-5-david@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
David Hildenbrand 2021-12-17 14:46:07 +01:00 committed by Michael S. Tsirkin
parent dba506788b
commit 89aec6411c
1 changed files with 10 additions and 2 deletions
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12
util/oslib-posix.c
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@ -40,6 +40,7 @@
#include <libgen.h>
#include "qemu/cutils.h"
#include "qemu/compiler.h"
#include "qemu/units.h"
#ifdef CONFIG_LINUX
#include <sys/syscall.h>
@ -525,7 +526,8 @@ static void *do_madv_populate_write_pages(void *arg)
return (void *)(uintptr_t)ret;
}
static inline int get_memset_num_threads(int smp_cpus)
static inline int get_memset_num_threads(size_t hpagesize, size_t numpages,
int smp_cpus)
{
long host_procs = sysconf(_SC_NPROCESSORS_ONLN);
int ret = 1;
@ -533,6 +535,12 @@ static inline int get_memset_num_threads(int smp_cpus)
if (host_procs > 0) {
ret = MIN(MIN(host_procs, MAX_MEM_PREALLOC_THREAD_COUNT), smp_cpus);
}
/* Especially with gigantic pages, don't create more threads than pages. */
ret = MIN(ret, numpages);
/* Don't start threads to prealloc comparatively little memory. */
ret = MIN(ret, MAX(1, hpagesize * numpages / (64 * MiB)));
/* In case sysconf() fails, we fall back to single threaded */
return ret;
}
@ -542,7 +550,7 @@ static int touch_all_pages(char *area, size_t hpagesize, size_t numpages,
{
static gsize initialized = 0;
MemsetContext context = {
.num_threads = get_memset_num_threads(smp_cpus),
.num_threads = get_memset_num_threads(hpagesize, numpages, smp_cpus),
};
size_t numpages_per_thread, leftover;
void *(*touch_fn)(void *);