Re: [PATCH/RFC 6/14] Reclaim Scalability: "No Reclaim LRU Infrastructure"

[mel@skynet.ie (Mel Gorman)]

On (17/09/07 11:41), Christoph Lameter didst pronounce:
> On Mon, 17 Sep 2007, Lee Schermerhorn wrote:
> 
> > > One fleeting thought here: It may be useful to *not* allocate known 
> > > unreclaimable pages with __GFP_MOVABLE.
> > 
> > Sorry, I don't understand where you're coming from here.
> > Non-reclaimable pages should be migratable, but maybe __GFP_MOVABLE
> > means something else?
> 
> True. __GFP_MOVABLE + MLOCK is movable.

Yes. Right now, it's rare we actually move them but the patches exist to
make it possible when we find it to be a real problem.

> Also the ramfs/shmem pages. There 
> may be uses though that require a page to stay put because it is used for 
> some nefarious I/O purpose by a driver. RDMA comes to mind.

Yeah :/

> Maybe we need 
> some additional option that works like MLOCK but forbids migration.

The problem with RDMA that I recall is that we don't know at allocation
time that they may be unmovable sometimes in the future. I didn't think
of a way around that problem.

> Those 
> would then be unreclaimable and not __GFP_MOVABLE. I know some of our 
> applications create huge amount of these.
> 

Can you think of a way that pages that will be later pinned by something
like RDMA can be identified in advance?

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab

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