linux-kernel - Re: Buffer allocation question

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Message-ID: <4C8F1BC8.4010201@ladisch.de>
Date:	Tue, 14 Sep 2010 08:52:56 +0200
From:	Clemens Ladisch <clemens@...isch.de>
To:	Ian Molton <ian.molton@...labora.co.uk>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: Buffer allocation question

Ian Molton wrote:
> I need to allocate some fairly large buffers which will be transferred 
> via virtio to a hypervisor.
> 
> the pages dont have to be contiguous physically and aside from the first 
> page int he transfer, the kernel wont really care about the contents of 
> the buffer.
> 
> the pages do need to be mapped into userspace contiguously, however. 

See drivers/firewire/core-iso.c, which uses fixed-size buffers.

> They are also often dynamically resized.
> ...
> my first thought (before realising how limited vmalloc space is) was to 
> vmalloc() them in my mmap() function, but this approach ran into trouble 
> when I discovered that the mmap() call does not get called if the vma 
> grows, so I cant then hook in and allocate more vmalloc() space.

You can set vma->vm_ops.

> the buffers will usually be filled all in one go, so it seems silly to 
> fault them in a page at a time.

AFAICS you don't have a choice when resizing.


Regards,
Clemens
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