linux-kernel - RE: [PATCH] proc: use vmalloc for our kernel buffer

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Date:   Thu, 13 Aug 2020 16:19:27 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Josef Bacik' <josef@...icpanda.com>, "hch@....de" <hch@....de>,
        "viro@...IV.linux.org.uk" <viro@...IV.linux.org.uk>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kernel-team@...com" <kernel-team@...com>
Subject: RE: [PATCH] proc: use vmalloc for our kernel buffer

From: Josef Bacik
> Sent: 13 August 2020 15:53
> 
>   sysctl: pass kernel pointers to ->proc_handler
> 
> we have been pre-allocating a buffer to copy the data from the proc
> handlers into, and then copying that to userspace.  The problem is this
> just blind kmalloc()'s the buffer size passed in from the read, which in
> the case of our 'cat' binary was 64kib.  Order-4 allocations are not
> awesome, and since we can potentially allocate up to our maximum order,
> use vmalloc for these buffers.

What happens if I run 'dd bs=16M ...' ?

	David

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