Message-ID: <43A0423E.60104@us.ibm.com>
Date: Wed, 14 Dec 2005 08:03:10 -0800
From: Matthew Dobson <colpatch@us.ibm.com>
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To: Andrea Arcangeli <andrea@suse.de>
CC: Pavel Machek <pavel@suse.cz>, linux-kernel@vger.kernel.org,
       Sridhar Samudrala <sri@us.ibm.com>, Andrew Morton <akpm@osdl.org>,
       Linux Memory Management <linux-mm@kvack.org>
Subject: Re: [RFC][PATCH 0/6] Critical Page Pool
References: <439FCECA.3060909@us.ibm.com> <20051214100841.GA18381@elf.ucw.cz> <20051214120152.GB5270@opteron.random>
In-Reply-To: <20051214120152.GB5270@opteron.random>
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Andrea Arcangeli wrote:
> On Wed, Dec 14, 2005 at 11:08:41AM +0100, Pavel Machek wrote:
> 
>>because reserved memory pool would have to be "sum of all network
>>interface bandwidths * ammount of time expected to survive without
>>network" which is way too much.
> 
> 
> Yes, a global pool isn't really useful. A per-subsystem pool would be
> more reasonable...

Which is an idea that I toyed with, as well.  The problem that I ran into
is how to tag an allocation as belonging to a specific subsystem.  For
example, in our code we need networking to use the critical pool.  How do
we let __alloc_pages() know what allocations belong to networking?
Networking needs named slab allocations, kmalloc allocations, and whole
page allocations to function.  Should each subsystem get it's own GFP flag
(GFP_NETWORKING, GFP_SCSI, GFP_SOUND, GFP_TERMINAL, ad nauseum)?  Should we
create these pools dynamically and pass a reference to which pool each
specific allocation uses (thus adding a parameter to all memory allocation
functions in the kernel)?  I realize that per-subsystem pools would be
better, but I thought about this for a while and couldn't come up with a
reasonable way to do it.


>>gigabytes into your machine. But don't go introducing infrastructure
>>that _can't_ be used right.
> 
> 
> Agreed, the current design of the patch can't be used right.

Well, it can for our use, but I recognize that isn't going to be a huge
selling point! :)  As I mentioned in my reply to Pavel, I'd really like to
find a way to design something that WOULD be generally useful.

Thanks!

-Matt
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