linux-kernel - Re: [PATCH v2 1/4] kernfs: kvmalloc xattr value instead of kmalloc

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Date:   Fri, 06 Mar 2020 00:49:51 -0800
From:   Joe Perches <joe@...ches.com>
To:     Daniel Xu <dxu@...uu.xyz>, cgroups@...r.kernel.org, tj@...nel.org,
        lizefan@...wei.com, hannes@...xchg.org
Cc:     shakeelb@...gle.com, linux-kernel@...r.kernel.org,
        gregkh@...uxfoundation.org, kernel-team@...com
Subject: Re: [PATCH v2 1/4] kernfs: kvmalloc xattr value instead of kmalloc

On Thu, 2020-03-05 at 13:16 -0800, Daniel Xu wrote:
> It's not really necessary to have contiguous physical memory for xattr
> values. We no longer need to worry about higher order allocations
> failing with kvmalloc, especially because the xattr size limit is at
> 64K.

So why use vmalloc memory at all?

> diff --git a/fs/xattr.c b/fs/xattr.c
']
> @@ -817,7 +817,7 @@ struct simple_xattr *simple_xattr_alloc(const void *value, size_t size)
>  	if (len < sizeof(*new_xattr))
>  		return NULL;
>  
> -	new_xattr = kmalloc(len, GFP_KERNEL);
> +	new_xattr = kvmalloc(len, GFP_KERNEL);

Why is this sensible?
vmalloc memory is a much more limited resource.

Also, it seems as if the function should set
new_xattr->name to NULL before the return.