Re: [PATCH 2/6] mm: support __GFP_REPEAT in kvmalloc_node for >=64kB

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Jan 12, 2017 at 04:37:13PM +0100, Michal Hocko wrote:
> From: Michal Hocko <mhocko@suse.com>
> 
> vhost code uses __GFP_REPEAT when allocating vhost_virtqueue resp.
> vhost_vsock because it would really like to prefer kmalloc to the
> vmalloc fallback - see 23cc5a991c7a ("vhost-net: extend device
> allocation to vmalloc") for more context. Michael Tsirkin has also
> noted:
> "
> __GFP_REPEAT overhead is during allocation time.  Using vmalloc means all
> accesses are slowed down.  Allocation is not on data path, accesses are.
> "
> 
> The similar applies to other vhost_kvzalloc users.
> 
> Let's teach kvmalloc_node to handle __GFP_REPEAT properly. There are two
> things to be careful about. First we should prevent from the OOM killer
> and so have to involve __GFP_NORETRY by default and secondly override
> __GFP_REPEAT for !costly order requests as the __GFP_REPEAT is ignored
> for !costly orders.
> 
> Supporting __GFP_REPEAT like semantic for !costly request is possible
> it would require changes in the page allocator. This is out of scope of
> this patch.
> 
> This patch shouldn't introduce any functional change.
> 
> Cc: "Michael S. Tsirkin" <mst@redhat.com>
> Acked-by: Vlastimil Babka <vbabka@suse.cz>
> Signed-off-by: Michal Hocko <mhocko@suse.com>


Acked-by: Michael S. Tsirkin <mst@redhat.com>

> ---
>  drivers/vhost/net.c   |  9 +++------
>  drivers/vhost/vhost.c | 15 +++------------
>  drivers/vhost/vsock.c |  9 +++------
>  mm/util.c             | 17 ++++++++++++++---
>  4 files changed, 23 insertions(+), 27 deletions(-)
> 
> diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
> index 5dc34653274a..105cd04c7414 100644
> --- a/drivers/vhost/net.c
> +++ b/drivers/vhost/net.c
> @@ -797,12 +797,9 @@ static int vhost_net_open(struct inode *inode, struct file *f)
>  	struct vhost_virtqueue **vqs;
>  	int i;
>  
> -	n = kmalloc(sizeof *n, GFP_KERNEL | __GFP_NOWARN | __GFP_REPEAT);
> -	if (!n) {
> -		n = vmalloc(sizeof *n);
> -		if (!n)
> -			return -ENOMEM;
> -	}
> +	n = kvmalloc(sizeof *n, GFP_KERNEL | __GFP_REPEAT);
> +	if (!n)
> +		return -ENOMEM;
>  	vqs = kmalloc(VHOST_NET_VQ_MAX * sizeof(*vqs), GFP_KERNEL);
>  	if (!vqs) {
>  		kvfree(n);
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index d6432603880c..d2bf8a41f55e 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -515,18 +515,9 @@ long vhost_dev_set_owner(struct vhost_dev *dev)
>  }
>  EXPORT_SYMBOL_GPL(vhost_dev_set_owner);
>  
> -static void *vhost_kvzalloc(unsigned long size)
> -{
> -	void *n = kzalloc(size, GFP_KERNEL | __GFP_NOWARN | __GFP_REPEAT);
> -
> -	if (!n)
> -		n = vzalloc(size);
> -	return n;
> -}
> -
>  struct vhost_umem *vhost_dev_reset_owner_prepare(void)
>  {
> -	return vhost_kvzalloc(sizeof(struct vhost_umem));
> +	return kvzalloc(sizeof(struct vhost_umem), GFP_KERNEL);
>  }
>  EXPORT_SYMBOL_GPL(vhost_dev_reset_owner_prepare);
>  
> @@ -1190,7 +1181,7 @@ EXPORT_SYMBOL_GPL(vhost_vq_access_ok);
>  
>  static struct vhost_umem *vhost_umem_alloc(void)
>  {
> -	struct vhost_umem *umem = vhost_kvzalloc(sizeof(*umem));
> +	struct vhost_umem *umem = kvzalloc(sizeof(*umem), GFP_KERNEL);
>  
>  	if (!umem)
>  		return NULL;
> @@ -1216,7 +1207,7 @@ static long vhost_set_memory(struct vhost_dev *d, struct vhost_memory __user *m)
>  		return -EOPNOTSUPP;
>  	if (mem.nregions > max_mem_regions)
>  		return -E2BIG;
> -	newmem = vhost_kvzalloc(size + mem.nregions * sizeof(*m->regions));
> +	newmem = kvzalloc(size + mem.nregions * sizeof(*m->regions), GFP_KERNEL);
>  	if (!newmem)
>  		return -ENOMEM;
>  
> diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
> index bbbf588540ed..7e0159867553 100644
> --- a/drivers/vhost/vsock.c
> +++ b/drivers/vhost/vsock.c
> @@ -455,12 +455,9 @@ static int vhost_vsock_dev_open(struct inode *inode, struct file *file)
>  	/* This struct is large and allocation could fail, fall back to vmalloc
>  	 * if there is no other way.
>  	 */
> -	vsock = kzalloc(sizeof(*vsock), GFP_KERNEL | __GFP_NOWARN | __GFP_REPEAT);
> -	if (!vsock) {
> -		vsock = vmalloc(sizeof(*vsock));
> -		if (!vsock)
> -			return -ENOMEM;
> -	}
> +	vsock = kvmalloc(sizeof(*vsock), GFP_KERNEL | __GFP_REPEAT);
> +	if (!vsock)
> +		return -ENOMEM;
>  
>  	vqs = kmalloc_array(ARRAY_SIZE(vsock->vqs), sizeof(*vqs), GFP_KERNEL);
>  	if (!vqs) {
> diff --git a/mm/util.c b/mm/util.c
> index 7e0c240b5760..9306244b9f41 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -333,7 +333,8 @@ EXPORT_SYMBOL(vm_mmap);
>   * Uses kmalloc to get the memory but if the allocation fails then falls back
>   * to the vmalloc allocator. Use kvfree for freeing the memory.
>   *
> - * Reclaim modifiers - __GFP_NORETRY, __GFP_REPEAT and __GFP_NOFAIL are not supported
> + * Reclaim modifiers - __GFP_NORETRY and __GFP_NOFAIL are not supported. __GFP_REPEAT
> + * is supported only for large (>64kB) allocations
>   */
>  void *kvmalloc_node(size_t size, gfp_t flags, int node)
>  {
> @@ -350,8 +351,18 @@ void *kvmalloc_node(size_t size, gfp_t flags, int node)
>  	 * Make sure that larger requests are not too disruptive - no OOM
>  	 * killer and no allocation failure warnings as we have a fallback
>  	 */
> -	if (size > PAGE_SIZE)
> -		kmalloc_flags |= __GFP_NORETRY | __GFP_NOWARN;
> +	if (size > PAGE_SIZE) {
> +		kmalloc_flags |= __GFP_NOWARN;
> +
> +		/*
> +		 * We have to override __GFP_REPEAT by __GFP_NORETRY for !costly
> +		 * requests because there is no other way to tell the allocator
> +		 * that we want to fail rather than retry endlessly.
> +		 */
> +		if (!(kmalloc_flags & __GFP_REPEAT) ||
> +				(size <= PAGE_SIZE << PAGE_ALLOC_COSTLY_ORDER))
> +			kmalloc_flags |= __GFP_NORETRY;
> +	}
>  
>  	ret = kmalloc_node(size, kmalloc_flags, node);
>  
> -- 
> 2.11.0