linux-kernel - Re: [RFC][PATCH 2/3] dma-buf: system_heap: Add pagepool support to system heap

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Date:   Mon, 21 Dec 2020 23:08:59 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     John Stultz <john.stultz@...aro.org>
Cc:     lkml <linux-kernel@...r.kernel.org>,
        Sandeep Patil <sspatil@...gle.com>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Ezequiel Garcia <ezequiel@...labora.com>,
        Robin Murphy <robin.murphy@....com>,
        James Jones <jajones@...dia.com>,
        Liam Mark <lmark@...eaurora.org>,
        Laura Abbott <labbott@...nel.org>,
        Chris Goldsworthy <cgoldswo@...eaurora.org>,
        Hridya Valsaraju <hridya@...gle.com>,
        Ørjan Eide <orjan.eide@....com>,
        linux-media <linux-media@...r.kernel.org>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Daniel Mentz <danielmentz@...gle.com>
Subject: Re: [RFC][PATCH 2/3] dma-buf: system_heap: Add pagepool support to
 system heap

On Fri, Dec 18, 2020 at 05:16:56PM -0800, John Stultz wrote:
> On Fri, Dec 18, 2020 at 6:36 AM Daniel Vetter <daniel@...ll.ch> wrote:
> > On Thu, Dec 17, 2020 at 11:06:11PM +0000, John Stultz wrote:
> > > Reuse/abuse the pagepool code from the network code to speed
> > > up allocation performance.
> > >
> > > This is similar to the ION pagepool usage, but tries to
> > > utilize generic code instead of a custom implementation.
> >
> > We also have one of these in ttm. I think we should have at most one of
> > these for the gpu ecosystem overall, maybe as a helper that can be plugged
> > into all the places.
> >
> > Or I'm kinda missing something, which could be since I only glanced at
> > yours for a bit. But it's also called page pool for buffer allocations,
> > and I don't think there's that many ways to implement that really :-)
> 
> Yea, when I was looking around the ttm one didn't seem quite as
> generic as the networking one, which more easily fit in here.

Oops, I didn't look that closely and didn't realize you're reusing the one
from net/core/.

> The main benefit for the system heap is not so much the pool itself
> (the normal page allocator is pretty good), as it being able to defer
> the free and zero the pages in a background thread, so the pool is
> effectively filled with pre-zeroed pages.
> 
> But I'll take another look at the ttm implementation and see if it can
> be re-used or the shared code refactored and pulled out somehow.

I think moving the page_pool from net into lib and using it in ttm might
also be an option. Lack of shrinker in the networking one might be a bit a
problem.

Also I guess the real fun will start if you pre-flush pages (after
zeroing) or use write-combined mode (which tends to be a real pain to
allocate). So for those I think we likely need more than just reusing the
one net/core has already.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch