Re: [PATCH RFC] v4l2-core: Use kvmalloc() for potentially big allocations

Marek Szyprowski <m.szyprowski@xxxxxxxxxxx> · Wed, 31 May 2017 14:09:29 +0200

Hi Tomasz,

On 2017-05-31 08:58, Tomasz Figa wrote:
There are multiple places where arrays or otherwise variable sized
buffer are allocated through V4L2 core code, including things like
controls, memory pages, staging buffers for ioctls and so on. Such
allocations can potentially require an order > 0 allocation from the
page allocator, which is not guaranteed to be fulfilled and is likely to
fail on a system with severe memory fragmentation (e.g. a system with
very long uptime).

Since the memory being allocated is intended to be used by the CPU
exclusively, we can consider using vmalloc() as a fallback and this is
exactly what the recently merged kvmalloc() helpers do. A kmalloc() call
is still attempted, even for order > 0 allocations, but it is done
with __GFP_NORETRY and __GFP_NOWARN, with expectation of failing if
requested memory is not available instantly. Only then the vmalloc()
fallback is used. This should give us fast and more reliable allocations
even on systems with higher memory pressure and/or more fragmentation,
while still retaining the same performance level on systems not
suffering from such conditions.

While at it, replace explicit array size calculations on changed
allocations with kvmalloc_array().

Signed-off-by: Tomasz Figa <tfiga@xxxxxxxxxxxx>
---
  drivers/media/v4l2-core/v4l2-async.c       |  4 ++--
  drivers/media/v4l2-core/v4l2-ctrls.c       | 25 +++++++++++++------------
  drivers/media/v4l2-core/v4l2-event.c       |  8 +++++---
  drivers/media/v4l2-core/v4l2-ioctl.c       |  6 +++---
  drivers/media/v4l2-core/v4l2-subdev.c      |  7 ++++---
  drivers/media/v4l2-core/videobuf2-dma-sg.c |  8 ++++----

For vb2:
Acked-by: Marek Szyprowski <m.szyprowski@xxxxxxxxxxx>

There are also a few vmalloc calls in old videobuf (v1) framework, which
might be converted to kvmalloc if you have a few spare minutes to take
a look.

  6 files changed, 31 insertions(+), 27 deletions(-)

diff --git a/drivers/media/v4l2-core/v4l2-async.c b/drivers/media/v4l2-core/v4l2-async.c
index 96cc733f35ef..2d2d9f1f8831 100644
--- a/drivers/media/v4l2-core/v4l2-async.c
+++ b/drivers/media/v4l2-core/v4l2-async.c
@@ -204,7 +204,7 @@ void v4l2_async_notifier_unregister(struct v4l2_async_notifier *notifier)
  	if (!notifier->v4l2_dev)
  		return;
  
-	dev = kmalloc_array(n_subdev, sizeof(*dev), GFP_KERNEL);
+	dev = kvmalloc_array(n_subdev, sizeof(*dev), GFP_KERNEL);
  	if (!dev) {
  		dev_err(notifier->v4l2_dev->dev,
  			"Failed to allocate device cache!\n");
@@ -260,7 +260,7 @@ void v4l2_async_notifier_unregister(struct v4l2_async_notifier *notifier)
  		}
  		put_device(d);
  	}
-	kfree(dev);
+	kvfree(dev);
  
  	notifier->v4l2_dev = NULL;
  
diff --git a/drivers/media/v4l2-core/v4l2-ctrls.c b/drivers/media/v4l2-core/v4l2-ctrls.c
index ec42872d11cf..88025527c67e 100644
--- a/drivers/media/v4l2-core/v4l2-ctrls.c
+++ b/drivers/media/v4l2-core/v4l2-ctrls.c
@@ -1745,8 +1745,9 @@ int v4l2_ctrl_handler_init_class(struct v4l2_ctrl_handler *hdl,
  	INIT_LIST_HEAD(&hdl->ctrls);
  	INIT_LIST_HEAD(&hdl->ctrl_refs);
  	hdl->nr_of_buckets = 1 + nr_of_controls_hint / 8;
-	hdl->buckets = kcalloc(hdl->nr_of_buckets, sizeof(hdl->buckets[0]),
-			       GFP_KERNEL);
+	hdl->buckets = kvmalloc_array(hdl->nr_of_buckets,
+				      sizeof(hdl->buckets[0]),
+				      GFP_KERNEL | __GFP_ZERO);
  	hdl->error = hdl->buckets ? 0 : -ENOMEM;
  	return hdl->error;
  }
@@ -1773,9 +1774,9 @@ void v4l2_ctrl_handler_free(struct v4l2_ctrl_handler *hdl)
  		list_del(&ctrl->node);
  		list_for_each_entry_safe(sev, next_sev, &ctrl->ev_subs, node)
  			list_del(&sev->node);
-		kfree(ctrl);
+		kvfree(ctrl);
  	}
-	kfree(hdl->buckets);
+	kvfree(hdl->buckets);
  	hdl->buckets = NULL;
  	hdl->cached = NULL;
  	hdl->error = 0;
@@ -2022,7 +2023,7 @@ static struct v4l2_ctrl *v4l2_ctrl_new(struct v4l2_ctrl_handler *hdl,
  		 is_array)
  		sz_extra += 2 * tot_ctrl_size;
  
-	ctrl = kzalloc(sizeof(*ctrl) + sz_extra, GFP_KERNEL);
+	ctrl = kvzalloc(sizeof(*ctrl) + sz_extra, GFP_KERNEL);
  	if (ctrl == NULL) {
  		handler_set_err(hdl, -ENOMEM);
  		return NULL;
@@ -2071,7 +2072,7 @@ static struct v4l2_ctrl *v4l2_ctrl_new(struct v4l2_ctrl_handler *hdl,
  	}
  
  	if (handler_new_ref(hdl, ctrl)) {
-		kfree(ctrl);
+		kvfree(ctrl);
  		return NULL;
  	}
  	mutex_lock(hdl->lock);
@@ -2824,8 +2825,8 @@ int v4l2_g_ext_ctrls(struct v4l2_ctrl_handler *hdl, struct v4l2_ext_controls *cs
  		return class_check(hdl, cs->which);
  
  	if (cs->count > ARRAY_SIZE(helper)) {
-		helpers = kmalloc_array(cs->count, sizeof(helper[0]),
-					GFP_KERNEL);
+		helpers = kvmalloc_array(cs->count, sizeof(helper[0]),
+					 GFP_KERNEL);
  		if (helpers == NULL)
  			return -ENOMEM;
  	}
@@ -2877,7 +2878,7 @@ int v4l2_g_ext_ctrls(struct v4l2_ctrl_handler *hdl, struct v4l2_ext_controls *cs
  	}
  
  	if (cs->count > ARRAY_SIZE(helper))
-		kfree(helpers);
+		kvfree(helpers);
  	return ret;
  }
  EXPORT_SYMBOL(v4l2_g_ext_ctrls);
@@ -3079,8 +3080,8 @@ static int try_set_ext_ctrls(struct v4l2_fh *fh, struct v4l2_ctrl_handler *hdl,
  		return class_check(hdl, cs->which);
  
  	if (cs->count > ARRAY_SIZE(helper)) {
-		helpers = kmalloc_array(cs->count, sizeof(helper[0]),
-					GFP_KERNEL);
+		helpers = kvmalloc_array(cs->count, sizeof(helper[0]),
+					 GFP_KERNEL);
  		if (!helpers)
  			return -ENOMEM;
  	}
@@ -3157,7 +3158,7 @@ static int try_set_ext_ctrls(struct v4l2_fh *fh, struct v4l2_ctrl_handler *hdl,
  	}
  
  	if (cs->count > ARRAY_SIZE(helper))
-		kfree(helpers);
+		kvfree(helpers);
  	return ret;
  }
  
diff --git a/drivers/media/v4l2-core/v4l2-event.c b/drivers/media/v4l2-core/v4l2-event.c
index a75df6cb141f..5f072ef8ff57 100644
--- a/drivers/media/v4l2-core/v4l2-event.c
+++ b/drivers/media/v4l2-core/v4l2-event.c
@@ -24,6 +24,7 @@
  #include <linux/sched.h>
  #include <linux/slab.h>
  #include <linux/export.h>
+#include <linux/mm.h>
  
  static unsigned sev_pos(const struct v4l2_subscribed_event *sev, unsigned idx)
  {
@@ -214,7 +215,8 @@ int v4l2_event_subscribe(struct v4l2_fh *fh,
  	if (elems < 1)
  		elems = 1;
  
-	sev = kzalloc(sizeof(*sev) + sizeof(struct v4l2_kevent) * elems, GFP_KERNEL);
+	sev = kvzalloc(sizeof(*sev) + sizeof(struct v4l2_kevent) * elems,
+		       GFP_KERNEL);
  	if (!sev)
  		return -ENOMEM;
  	for (i = 0; i < elems; i++)
@@ -232,7 +234,7 @@ int v4l2_event_subscribe(struct v4l2_fh *fh,
  	spin_unlock_irqrestore(&fh->vdev->fh_lock, flags);
  
  	if (found_ev) {
-		kfree(sev);
+		kvfree(sev);
  		return 0; /* Already listening */
  	}
  
@@ -304,7 +306,7 @@ int v4l2_event_unsubscribe(struct v4l2_fh *fh,
  	if (sev && sev->ops && sev->ops->del)
  		sev->ops->del(sev);
  
-	kfree(sev);
+	kvfree(sev);
  
  	return 0;
  }
diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
index e5a2187381db..098e8be36ea6 100644
--- a/drivers/media/v4l2-core/v4l2-ioctl.c
+++ b/drivers/media/v4l2-core/v4l2-ioctl.c
@@ -2811,7 +2811,7 @@ video_usercopy(struct file *file, unsigned int cmd, unsigned long arg,
  			parg = sbuf;
  		} else {
  			/* too big to allocate from stack */
-			mbuf = kmalloc(_IOC_SIZE(cmd), GFP_KERNEL);
+			mbuf = kvmalloc(_IOC_SIZE(cmd), GFP_KERNEL);
  			if (NULL == mbuf)
  				return -ENOMEM;
  			parg = mbuf;
@@ -2858,7 +2858,7 @@ video_usercopy(struct file *file, unsigned int cmd, unsigned long arg,
  		 * array) fits into sbuf (so that mbuf will still remain
  		 * unused up to here).
  		 */
-		mbuf = kmalloc(array_size, GFP_KERNEL);
+		mbuf = kvmalloc(array_size, GFP_KERNEL);
  		err = -ENOMEM;
  		if (NULL == mbuf)
  			goto out_array_args;
@@ -2901,7 +2901,7 @@ video_usercopy(struct file *file, unsigned int cmd, unsigned long arg,
  	}
  
  out:
-	kfree(mbuf);
+	kvfree(mbuf);
  	return err;
  }
  EXPORT_SYMBOL(video_usercopy);
diff --git a/drivers/media/v4l2-core/v4l2-subdev.c b/drivers/media/v4l2-core/v4l2-subdev.c
index da78497ae5ed..053d06bb407d 100644
--- a/drivers/media/v4l2-core/v4l2-subdev.c
+++ b/drivers/media/v4l2-core/v4l2-subdev.c
@@ -577,13 +577,14 @@ v4l2_subdev_alloc_pad_config(struct v4l2_subdev *sd)
  	if (!sd->entity.num_pads)
  		return NULL;
  
-	cfg = kcalloc(sd->entity.num_pads, sizeof(*cfg), GFP_KERNEL);
+	cfg = kvmalloc_array(sd->entity.num_pads, sizeof(*cfg),
+			     GFP_KERNEL | __GFP_ZERO);
  	if (!cfg)
  		return NULL;
  
  	ret = v4l2_subdev_call(sd, pad, init_cfg, cfg);
  	if (ret < 0 && ret != -ENOIOCTLCMD) {
-		kfree(cfg);
+		kvfree(cfg);
  		return NULL;
  	}
  
@@ -593,7 +594,7 @@ EXPORT_SYMBOL_GPL(v4l2_subdev_alloc_pad_config);
  
  void v4l2_subdev_free_pad_config(struct v4l2_subdev_pad_config *cfg)
  {
-	kfree(cfg);
+	kvfree(cfg);
  }
  EXPORT_SYMBOL_GPL(v4l2_subdev_free_pad_config);
  #endif /* CONFIG_MEDIA_CONTROLLER */
diff --git a/drivers/media/v4l2-core/videobuf2-dma-sg.c b/drivers/media/v4l2-core/videobuf2-dma-sg.c
index 8e8798a74760..5defa1f22ca2 100644
--- a/drivers/media/v4l2-core/videobuf2-dma-sg.c
+++ b/drivers/media/v4l2-core/videobuf2-dma-sg.c
@@ -120,8 +120,8 @@ static void *vb2_dma_sg_alloc(struct device *dev, unsigned long dma_attrs,
  	buf->num_pages = size >> PAGE_SHIFT;
  	buf->dma_sgt = &buf->sg_table;
  
-	buf->pages = kzalloc(buf->num_pages * sizeof(struct page *),
-			     GFP_KERNEL);
+	buf->pages = kvmalloc_array(buf->num_pages, sizeof(struct page *),
+				    GFP_KERNEL | __GFP_ZERO);
  	if (!buf->pages)
  		goto fail_pages_array_alloc;
  
@@ -165,7 +165,7 @@ static void *vb2_dma_sg_alloc(struct device *dev, unsigned long dma_attrs,
  	while (num_pages--)
  		__free_page(buf->pages[num_pages]);
  fail_pages_alloc:
-	kfree(buf->pages);
+	kvfree(buf->pages);
  fail_pages_array_alloc:
  	kfree(buf);
  	return ERR_PTR(-ENOMEM);
@@ -187,7 +187,7 @@ static void vb2_dma_sg_put(void *buf_priv)
  		sg_free_table(buf->dma_sgt);
  		while (--i >= 0)
  			__free_page(buf->pages[i]);
-		kfree(buf->pages);
+		kvfree(buf->pages);
  		put_device(buf->dev);
  		kfree(buf);
  	}

Best regards
--
Marek Szyprowski, PhD
Samsung R&D Institute Poland







