linux-kernel - Re: [PATCH 2/6] mm: support __GFP_REPEAT in kvmalloc

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Date:   Sat, 14 Jan 2017 11:42:09 +0900
From:   Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To:     Michal Hocko <mhocko@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Vlastimil Babka <vbabka@...e.cz>,
        David Rientjes <rientjes@...gle.com>,
        Mel Gorman <mgorman@...e.de>,
        Johannes Weiner <hannes@...xchg.org>,
        Al Viro <viro@...iv.linux.org.uk>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>,
        Michal Hocko <mhocko@...e.com>,
        "Michael S. Tsirkin" <mst@...hat.com>
Subject: Re: [PATCH 2/6] mm: support __GFP_REPEAT in kvmalloc_node for >=64kB

On 2017/01/13 0:37, Michal Hocko wrote:
> 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);

An opportunity to standardize as sizeof(*n) like other allocations.

> 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

Isn't this ">32kB" (i.e. __GFP_REPEAT is supported for 64kB allocation) ?

>   */
>  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);
>  
>