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

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Date:   Fri, 6 Mar 2020 10:37:20 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Joe Perches <joe@...ches.com>
Cc:     Daniel Xu <dxu@...uu.xyz>, cgroups@...r.kernel.org, tj@...nel.org,
        lizefan@...wei.com, hannes@...xchg.org, shakeelb@...gle.com,
        linux-kernel@...r.kernel.org, kernel-team@...com
Subject: Re: [PATCH v2 1/4] kernfs: kvmalloc xattr value instead of kmalloc

On Fri, Mar 06, 2020 at 12:49:51AM -0800, Joe Perches wrote:
> 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?

See the thread on v1

> vmalloc memory is a much more limited resource.

Large chunks of "len" is much more limited :)

thanks,

greg k-h