[PATCH v3 5/9] block/block-copy: don't reserve memory for zero tasks

["Denis V. Lunev" <den@openvz.org>]

From: Denis V. Lunev <den@openvz.org>

block_copy_dirty_clusters() charges task->req.bytes to the shared memory
pool for every task, but a COPY_WRITE_ZEROES task allocates no bounce
buffer, so there is nothing to account for. Add
block_copy_task_shres_bytes() and use it at all three call sites.

Zero tasks lose the throttling the pool gave them incidentally and are
bounded only by BLOCK_COPY_MAX_WORKERS (64).

Reviewed-by: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>
Signed-off-by: Denis V. Lunev <den@openvz.org>
CC: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
CC: John Snow <jsnow@redhat.com>
CC: Andrey Drobyshev <andrey.drobyshev@virtuozzo.com>
---
 block/block-copy.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/block/block-copy.c b/block/block-copy.c
index 1826c2e1c7..21ebe8aec2 100644
--- a/block/block-copy.c
+++ b/block/block-copy.c
@@ -453,6 +453,11 @@ void block_copy_set_progress_meter(BlockCopyState *s, ProgressMeter *pm)
     s->progress = pm;
 }
 
+static uint64_t block_copy_task_shres_bytes(BlockCopyTask *task)
+{
+    return task->method == COPY_WRITE_ZEROES ? 0 : task->req.bytes;
+}
+
 /*
  * Takes ownership of @task
  *
@@ -474,7 +479,7 @@ static coroutine_fn int block_copy_task_run(AioTaskPool *pool,
 
     aio_task_pool_wait_slot(pool);
     if (aio_task_pool_status(pool) < 0) {
-        co_put_to_shres(task->s->mem, task->req.bytes);
+        co_put_to_shres(task->s->mem, block_copy_task_shres_bytes(task));
         block_copy_task_end(task, -ECANCELED);
         g_free(task);
         return -ECANCELED;
@@ -605,7 +610,7 @@ static coroutine_fn int block_copy_task_entry(AioTask *task)
             progress_work_done(s->progress, t->req.bytes);
         }
     }
-    co_put_to_shres(s->mem, t->req.bytes);
+    co_put_to_shres(s->mem, block_copy_task_shres_bytes(t));
     block_copy_task_end(t, ret);
 
     if (s->discard_source && ret == 0) {
@@ -816,7 +821,7 @@ block_copy_dirty_clusters(BlockCopyCallState *call_state)
 
         trace_block_copy_process(s, task->req.offset);
 
-        co_get_from_shres(s->mem, task->req.bytes);
+        co_get_from_shres(s->mem, block_copy_task_shres_bytes(task));
 
         offset = task_end(task);
         bytes = end - offset;
-- 
2.53.0