Re: [RFC][PATCH 0/5] VM_PINNED

[Peter Zijlstra]

On Tue, May 27, 2014 at 03:00:15PM -0500, Christoph Lameter wrote:
> On Tue, 27 May 2014, Peter Zijlstra wrote:
> 
> > > What do you mean by shared pages that are not shmem pages? AnonPages that
> > > are referenced from multiple processes?
> >
> > Regular files.. they get allocated through __page_cache_alloc(). AFAIK
> > there is nothing stopping people from pinning file pages for RDMA or
> > other purposes. Unusual maybe, but certainly not impossible, and
> > therefore we must be able to handle it.
> 
> Typically structures for RDMA are allocated on the heap.

Sure, typically. But that's not enough.

> The main use case is pinnning the executable pages in the page cache?

No.. although that's one of the things the -rt people are interested in.

> > > Migration is expensive and the memory registration overhead already
> > > causes lots of complaints.
> >
> > Sure, but first to the simple thing, then if its a problem do something
> > else.
> 
> I thought the main issue here were the pinning of IB/RDMA buffers.

It is,.. but you have to deal with the generic case before you go off
doing specific things.

You're approaching the problem from the wrong way; first make it such
that everything works, only then, optimize some specific case, if and
when it becomes important.

Don't start by only looking at the one specific case you're interested
in and forget about everything else.

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