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[Qemu-devel] [RFC v2 03/32] migrate: Update ram_block_discard_range for
From: |
Dr. David Alan Gilbert (git) |
Subject: |
[Qemu-devel] [RFC v2 03/32] migrate: Update ram_block_discard_range for shared |
Date: |
Thu, 24 Aug 2017 20:27:01 +0100 |
From: "Dr. David Alan Gilbert" <address@hidden>
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 <address@hidden>
---
exec.c | 35 ++++++++++++++++++++++++-----------
trace-events | 3 +++
2 files changed, 27 insertions(+), 11 deletions(-)
diff --git a/exec.c b/exec.c
index d20c34ca83..67df2909ce 100644
--- a/exec.c
+++ b/exec.c
@@ -3573,6 +3573,7 @@ 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",
@@ -3582,23 +3583,35 @@ 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);
+ need_fallocate = rb->fd != -1;
+ if (need_fallocate) {
+ /* For a file, this causes the area of the file to be zero'd
+ * if read, and for hugetlbfs also causes it to be unmapped
+ * so a userfault will trigger.
*/
#ifdef CONFIG_FALLOCATE_PUNCH_HOLE
ret = fallocate(rb->fd, FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
start, length);
#endif
}
+ /* i.e. need madvise but skip it if the fallocate failed */
+ if (need_madvise && (!need_fallocate || (ret == 0))) {
+ /* For normal RAM this causes it to be unmapped,
+ * for shared memory it causes the local mapping to disappear
+ * and to fall back on the file contents (which we just
+ * fallocate'd away).
+ */
+#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 1f50f56d9d..213ee34f89 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) "address@hidden: 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 0x%"PRIx64" value 0x%"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 0x%"PRIx64" value 0x%"PRIx64" size %u"
--
2.13.5
- [Qemu-devel] [RFC v2 00/32] postcopy+vhost-user/shared ram, Dr. David Alan Gilbert (git), 2017/08/24
- [Qemu-devel] [RFC v2 02/32] vhub: Only process received packets on started queues, Dr. David Alan Gilbert (git), 2017/08/24
- [Qemu-devel] [RFC v2 01/32] vhu: vu_queue_started, Dr. David Alan Gilbert (git), 2017/08/24
- [Qemu-devel] [RFC v2 03/32] migrate: Update ram_block_discard_range for shared,
Dr. David Alan Gilbert (git) <=
- [Qemu-devel] [RFC v2 04/32] qemu_ram_block_host_offset, Dr. David Alan Gilbert (git), 2017/08/24
- [Qemu-devel] [RFC v2 05/32] migration/ram: ramblock_recv_bitmap_test_byte_offset, Dr. David Alan Gilbert (git), 2017/08/24
- [Qemu-devel] [RFC v2 06/32] postcopy: use UFFDIO_ZEROPAGE only when available, Dr. David Alan Gilbert (git), 2017/08/24
- [Qemu-devel] [RFC v2 07/32] postcopy: Add notifier chain, Dr. David Alan Gilbert (git), 2017/08/24