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[Qemu-devel] [RFC 02/29] migrate: Update ram_block_discard_range for sha


From: Dr. David Alan Gilbert (git)
Subject: [Qemu-devel] [RFC 02/29] migrate: Update ram_block_discard_range for shared
Date: Wed, 28 Jun 2017 20:00:20 +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       | 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) "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 %#"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




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