Re: [RFC][PATCH 0/6] Critical Page Pool

[Matthew Dobson <colpatch@us.ibm.com>]

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