[Qemu-devel] [PATCH v3 05/16] postcopy: enhance ram_block_discard_range for hugepages

["Dr. David Alan Gilbert (git)" <dgilbert@redhat.com>]

From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>

Unfortunately madvise DONTNEED doesn't work on hugepagetlb
so use fallocate(FALLOC_FL_PUNCH_HOLE)
qemu_fd_getpagesize only sets the page based off a file
if the file is from hugetlbfs.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Laurent Vivier <lvivier@redhat.com>
---
 exec.c | 24 ++++++++++++++++++++----
 1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/exec.c b/exec.c
index ddbc314..ec3a11f 100644
--- a/exec.c
+++ b/exec.c
@@ -46,6 +46,11 @@
 #include "sysemu/xen-mapcache.h"
 #include "trace-root.h"
 
+#ifdef CONFIG_FALLOCATE_PUNCH_HOLE
+#include <fcntl.h>
+#include <linux/falloc.h>
+#endif
+
 #endif
 #include "exec/cpu-all.h"
 #include "qemu/rcu_queue.h"
@@ -3320,12 +3325,23 @@ int ram_block_discard_range(RAMBlock *rb, uint64_t start, size_t length)
 
         errno = ENOTSUP; /* If we are missing MADVISE etc */
 
+        if (rb->page_size == qemu_host_page_size) {
 #if defined(CONFIG_MADVISE)
-        /* Note: We need the madvise MADV_DONTNEED behaviour of definitely
-         * freeing the page.
-         */
-        ret = madvise(host_startaddr, length, MADV_DONTNEED);
+            /* Note: We need the madvise MADV_DONTNEED behaviour of definitely
+             * freeing the page.
+             */
+            ret = madvise(host_startaddr, length, MADV_DONTNEED);
 #endif
+        } else {
+            /* Huge page case  - unfortunately it can't do DONTNEED, but
+             * it can do the equivalent by FALLOC_FL_PUNCH_HOLE in the
+             * huge page file.
+             */
+#ifdef CONFIG_FALLOCATE_PUNCH_HOLE
+            ret = fallocate(rb->fd, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
+                            start, length);
+#endif
+        }
         if (ret) {
             ret = -errno;
             error_report("ram_block_discard_range: Failed to discard range "
-- 
2.9.3