linux-kernel - Re: Problem: Out of memory after 2days with 2GB RAM

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Date:	Thu, 12 Jun 2008 20:35:48 +0300
From:	"Tomas Winkler" <tomasw@...il.com>
To:	"Johannes Berg" <johannes@...solutions.net>
Cc:	"Rik van Riel" <riel@...hat.com>,
	"Zdenek Kabelac" <zdenek.kabelac@...il.com>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	yi.zhu@...el.com, reinette.chatre@...el.com,
	linux-wireless@...r.kernel.org
Subject: Re: Problem: Out of memory after 2days with 2GB RAM

On Thu, Jun 12, 2008 at 8:03 PM, Johannes Berg
<johannes@...solutions.net> wrote:
>
>> > Try the patch below. It should improve code generation too.
>> >
>> > I discussed this with Tomas previously and he says the hw is capable of
>> > doing 20 fragments per frame (wonder why, Broadcom can do an unlimited
>> > number...) but he complained about the networking stack not being able
>> > to.
>>
>> This is scatter gather buffers that can be kicked in one DMA transaction.
>>
>> Well, the hardware needs to support IP checksumming for that, hence,
>> > afaik, only two fragments can ever be used (one for hw header, one for
>> > frame)
>> This I still don't understand why but everybody is already tired to
>> explaining me why.. :) Just need to find time to dig into it.
>
> And you can safely decrease the allocation to 10% as I do in my patch
> because once you understand you'll see that you cannot possibly use
> more. Hence, you can ack this patch ;)
>
>> > This cuts the allocation to 10%, or (under) a page in all cases.
>>
>> Probably. it would be safe to use vmalloc for allocating txb anyway.
>> I'll give it a try.
>
> Yeah, but why bother if we can just allocate 10% of the size, waste a
> lot less memory etc. mac80211 isn't going to pass in a scatter/gather
> frame anyway.

Hope never dies. I actually have seen this speed up the throughput so
I will dig into it anyway.

>> There was already discussion on LKML about memory allocation problems
>> on X86_64, which might explain this regression. This didn't happen
>> before.
>
> Doesn't really matter, iwlwifi is _wasting_ this allocation, it cannot
> possibly use all those buffers anyway.

This matter actually for consistent allocation.

> The more interesting thing is the pci_alloc_consistent allocation right
> below that is also _huge_, but that's because of the stupid hardware
> design, or can the hardware cope with having the descriptors non-linear
> in memory?

We talk after your next HW design. How will configure 265 * 16
descriptors separately.

Tomas
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