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

[Peter Zijlstra]

On Tue, May 27, 2014 at 12:19:16AM +0400, Konstantin Khlebnikov wrote:
> On Mon, May 26, 2014 at 6:56 PM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> > Hi all,
> >
> > I mentioned at LSF/MM that I wanted to revive this, and at the time there were
> > no disagreements.
> >
> > I finally got around to refreshing the patch(es) so here goes.
> >
> > These patches introduce VM_PINNED infrastructure, vma tracking of persistent
> > 'pinned' page ranges. Pinned is anything that has a fixed phys address (as
> > required for say IO DMA engines) and thus cannot use the weaker VM_LOCKED. One
> > popular way to pin pages is through get_user_pages() but that not nessecarily
> > the only way.
> 
> Lol, this looks like resurrection of VM_RESERVED which I've removed
> not so long time ago.

Not sure what VM_RESERVED did, but there might be a similarity.

> Maybe single-bit state isn't flexible enought?

Not sure what you mean, the one bit is perfectly fine for what I want it
to do.

> This supposed to supports pinning only by one user and only in its own mm?

Pretty much, that's adequate for all users I'm aware of and mirrors the
mlock semantics.

> This might be done as extension of existing memory-policy engine.
> It allows to keep vm_area_struct slim in normal cases and change
> behaviour when needed.
> memory-policy might hold reference-counter of "pinners", track
> ownership and so on.

That all sounds like raping the mempolicy code and massive over
engineering.

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