linux-kernel - Re: [PATCH 8/9] dspbridge: add map support for big buffers

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Message-ID: <AANLkTikQCTtwOkAmt3PZrOkxi=VzJtfNKGsH=YXawt9t@mail.gmail.com>
Date:	Wed, 25 Aug 2010 00:17:50 +0300
From:	Felipe Contreras <felipe.contreras@...il.com>
To:	"Guzman Lugo, Fernando" <fernando.lugo@...com>
Cc:	"Kanigeri, Hari" <h-kanigeri2@...com>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"ohad@...ery.com" <ohad@...ery.com>,
	"hiroshi.doyu@...ia.com" <hiroshi.doyu@...ia.com>,
	"ameya.palande@...ia.com" <ameya.palande@...ia.com>,
	"felipe.contreras@...ia.com" <felipe.contreras@...ia.com>
Subject: Re: [PATCH 8/9] dspbridge: add map support for big buffers

On Tue, Aug 24, 2010 at 10:30 PM, Guzman Lugo, Fernando
<fernando.lugo@...com> wrote:
>> Oh, I actually meant the DMM pool.
>>
>> a) 1. Migrate to iommu, 2. Remove DMM completely
>> b) 1. Remove DMM pool, 2. Migrate to iommu 3. Remove DMM completely
>
> Ok, what is the issue with DMM pool?

>From what I've heard; fragmentation.

> The issue I see removing DMM pool in this moment and making all the DMM
> Available (from 0x11000000 to 0xFFFFFFFF omap3 case) that is:
>
> The DMM module allocates a list of "struct map_page" elements base on
> DMM_POOL_SIZE to keep track of memory reserved and mapped.
>
> Memory allocated = DMM_POOL_SIZE / PAGE_SIZE * sizeof(struct map_page);
>
> So making all memory avalible it will increase the memory used for DMM
> Module and it could be quite significant.
>
> Iovmm.c module, the list is increased dynamically when it is needed so
> It does no have that problem. Then when the migration is done and
> Iovmm.c module is used the DMM_POOL_SIZE can be removed without issues.

It seems that this "memory allocated" you are taking about is an
array, but what we would like is a list, like apparently iovmm is
using. I think I can give that a try if needed.

However, from what I can see iovmm can be used instead of dmm even if
the switch to iommu is not yet there.

-- 
Felipe Contreras
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