[Qemu-devel] [RFC PATCH 10/16] qcow2: Delay the COW

[Kevin Wolf <kwolf@redhat.com>]

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 block/qcow2-cluster.c |   29 +++++++++++++++++++++++++++++
 block/qcow2.c         |   31 ++++++++++++++++++++++++++++---
 block/qcow2.h         |   10 ++++++++++
 3 files changed, 67 insertions(+), 3 deletions(-)

diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index a89d68d..0f50888 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -791,6 +791,34 @@ out:
     return i;
 }
 
+struct KickL2Meta {
+    QEMUBH *bh;
+    QCowL2Meta *m;
+};
+
+static void kick_l2meta_bh(void *opaque)
+{
+    struct KickL2Meta *k = opaque;
+    QCowL2Meta *m = k->m;
+
+    qemu_bh_delete(k->bh);
+    free(k);
+
+    if (m->sleeping) {
+        qemu_coroutine_enter(m->co, NULL);
+    }
+}
+
+static void kick_l2meta(QCowL2Meta *m)
+{
+    struct KickL2Meta *k = g_malloc(sizeof(*k));
+
+    k->bh = qemu_bh_new(kick_l2meta_bh, k);
+    k->m = m;
+
+    qemu_bh_schedule(k->bh);
+}
+
 /*
  * Check if there already is an AIO write request in flight which allocates
  * the same cluster. In this case we need to wait until the previous
@@ -823,6 +851,7 @@ static int handle_dependencies(BlockDriverState *bs, uint64_t guest_offset,
                 /* Wait for the dependency to complete. We need to recheck
                  * the free/allocated clusters when we continue. */
                 qemu_co_mutex_unlock(&s->lock);
+                kick_l2meta(old_alloc);
                 qemu_co_queue_wait(&old_alloc->dependent_requests);
                 qemu_co_mutex_lock(&s->lock);
                 return -EAGAIN;
diff --git a/block/qcow2.c b/block/qcow2.c
index f9881d0..2e220c7 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -765,6 +765,12 @@ static void coroutine_fn process_l2meta(void *opaque)
     BDRVQcowState *s = bs->opaque;
     int ret;
 
+    if (!s->in_l2meta_flush) {
+        m->sleeping = true;
+        co_sleep_ns(rt_clock, 1000000);
+        m->sleeping = false;
+    }
+
     qemu_co_mutex_lock(&s->lock);
 
     ret = qcow2_alloc_cluster_link_l2(bs, m);
@@ -781,17 +787,37 @@ static void coroutine_fn process_l2meta(void *opaque)
 
 static inline coroutine_fn void stop_l2meta(BDRVQcowState *s)
 {
+    QCowL2Meta *m;
+
+    s->in_l2meta_flush = true;
+again:
+    QLIST_FOREACH(m, &s->cluster_allocs, next_in_flight) {
+        if (m->sleeping) {
+            qemu_coroutine_enter(m->co, NULL);
+            /* next_in_flight link could have become invalid */
+            goto again;
+        }
+    }
+
     qemu_co_rwlock_wrlock(&s->l2meta_flush);
 }
 
 static inline coroutine_fn void resume_l2meta(BDRVQcowState *s)
 {
+    s->in_l2meta_flush = false;
     qemu_co_rwlock_unlock(&s->l2meta_flush);
 }
 
 static bool qcow2_drain(BlockDriverState *bs)
 {
     BDRVQcowState *s = bs->opaque;
+    QCowL2Meta *m;
+
+    QLIST_FOREACH(m, &s->cluster_allocs, next_in_flight) {
+        if (m->sleeping) {
+            qemu_coroutine_enter(m->co, NULL);
+        }
+    }
 
     return !QLIST_EMPTY(&s->cluster_allocs);
 }
@@ -876,7 +902,6 @@ static coroutine_fn int qcow2_co_writev(BlockDriverState *bs,
         }
 
         if (l2meta != NULL) {
-            Coroutine *co;
             ProcessL2Meta p = {
                 .bs = bs,
                 .m  = l2meta,
@@ -886,8 +911,8 @@ static coroutine_fn int qcow2_co_writev(BlockDriverState *bs,
             qemu_co_rwlock_rdlock(&s->l2meta_flush);
 
             l2meta->is_written = true;
-            co = qemu_coroutine_create(process_l2meta);
-            qemu_coroutine_enter(co, &p);
+            l2meta->co = qemu_coroutine_create(process_l2meta);
+            qemu_coroutine_enter(l2meta->co, &p);
 
             l2meta = NULL;
             qemu_co_mutex_lock(&s->lock);
diff --git a/block/qcow2.h b/block/qcow2.h
index 73dac17..8bf145c 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -169,6 +169,7 @@ typedef struct BDRVQcowState {
      * Writers: Anyone who requires l2meta to be flushed
      */
     CoRwlock l2meta_flush;
+    bool in_l2meta_flush;
 
     uint32_t crypt_method; /* current crypt method, 0 if no key yet */
     uint32_t crypt_method_header;
@@ -245,6 +246,15 @@ typedef struct QCowL2Meta
     bool is_written;
 
     /**
+     * true if the request is sleeping in the COW delay and the coroutine may
+     * be reentered in order to cancel the timer.
+     */
+    bool sleeping;
+
+    /** Coroutine that handles delayed COW and updates L2 entry */
+    Coroutine *co;
+
+    /**
      * Requests that overlap with this allocation and wait to be restarted
      * when the allocating request has completed.
      */
-- 
1.7.6.5