From: "Dr. David Alan Gilbert" <dgilb...@redhat.com>
The choice of call to discard a block is getting more complicated
for other cases. We use fallocate PUNCH_HOLE in any file cases;
it works for both hugepage and for tmpfs.
We use the DONTNEED for non-hugepage cases either where they're
anonymous or where they're private.
Care should be taken when trying other backing files.
Signed-off-by: Dr. David Alan Gilbert <dgilb...@redhat.com>
---
exec.c | 28 ++++++++++++++++------------
trace-events | 3 +++
2 files changed, 19 insertions(+), 12 deletions(-)
diff --git a/exec.c b/exec.c
index 69fc5c9b07..4e61226a16 100644
--- a/exec.c
+++ b/exec.c
@@ -3557,6 +3557,7 @@ int ram_block_discard_range(RAMBlock *rb, uint64_t start,
size_t length)
}
if ((start + length) <= rb->used_length) {
+ bool need_madvise, need_fallocate;
uint8_t *host_endaddr = host_startaddr + length;
if ((uintptr_t)host_endaddr & (rb->page_size - 1)) {
error_report("ram_block_discard_range: Unaligned end address: %p",
@@ -3566,23 +3567,26 @@ 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);
-#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.
- */
+ /* The logic here is messy;
+ * madvise DONTNEED fails for hugepages
+ * fallocate works on hugepages and shmem
+ */
+ need_madvise = (rb->page_size == qemu_host_page_size) &&
+ (rb->fd == -1 || !(rb->flags & RAM_SHARED));
+ need_fallocate = rb->fd != -1;
+ if (ret == -1 && need_fallocate) {
#ifdef CONFIG_FALLOCATE_PUNCH_HOLE
ret = fallocate(rb->fd, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
start, length);
#endif
}
+ if (need_madvise && (!need_fallocate || (ret == 0))) {
+#if defined(CONFIG_MADVISE)
+ ret = madvise(host_startaddr, length, MADV_DONTNEED);
+#endif
+ }
+ trace_ram_block_discard_range(rb->idstr, host_startaddr,
+ need_madvise, need_fallocate, ret);
if (ret) {
ret = -errno;
error_report("ram_block_discard_range: Failed to discard range "
diff --git a/trace-events b/trace-events
index bae63fdb1d..2c6e8d2160 100644
--- a/trace-events
+++ b/trace-events
@@ -55,6 +55,9 @@ dma_complete(void *dbs, int ret, void *cb) "dbs=%p ret=%d
cb=%p"
dma_blk_cb(void *dbs, int ret) "dbs=%p ret=%d"
dma_map_wait(void *dbs) "dbs=%p"
+# exec.c
+ram_block_discard_range(const char *rbname, void *hva, bool need_madvise, bool
need_fallocate, int ret) "%s@%p: madvise: %d fallocate: %d ret: %d"
+
# memory.c
memory_region_ops_read(int cpu_index, void *mr, uint64_t addr, uint64_t value,
unsigned size) "cpu %d mr %p addr %#"PRIx64" value %#"PRIx64" size %u"
memory_region_ops_write(int cpu_index, void *mr, uint64_t addr, uint64_t
value, unsigned size) "cpu %d mr %p addr %#"PRIx64" value %#"PRIx64" size %u"
--
2.13.0
