Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Mon, 21 Dec 2020 23:08:59 +0100
From:   Daniel Vetter <daniel@ffwll.ch>
To:     John Stultz <john.stultz@linaro.org>
Cc:     lkml <linux-kernel@vger.kernel.org>,
        Sandeep Patil <sspatil@google.com>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        Ezequiel Garcia <ezequiel@collabora.com>,
        Robin Murphy <robin.murphy@arm.com>,
        James Jones <jajones@nvidia.com>,
        Liam Mark <lmark@codeaurora.org>,
        Laura Abbott <labbott@kernel.org>,
        Chris Goldsworthy <cgoldswo@codeaurora.org>,
        Hridya Valsaraju <hridya@google.com>,
        =?iso-8859-1?Q?=D8rjan?= Eide <orjan.eide@arm.com>,
        linux-media <linux-media@vger.kernel.org>,
        Suren Baghdasaryan <surenb@google.com>,
        Daniel Mentz <danielmentz@google.com>
Subject: Re: [RFC][PATCH 2/3] dma-buf: system_heap: Add pagepool support to
 system heap
Message-ID: <X+Ec+xVhyIUa7IsJ@phenom.ffwll.local>
Mail-Followup-To: John Stultz <john.stultz@linaro.org>,
        lkml <linux-kernel@vger.kernel.org>,
        Sandeep Patil <sspatil@google.com>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        Ezequiel Garcia <ezequiel@collabora.com>,
        Robin Murphy <robin.murphy@arm.com>,
        James Jones <jajones@nvidia.com>, Liam Mark <lmark@codeaurora.org>,
        Laura Abbott <labbott@kernel.org>,
        Chris Goldsworthy <cgoldswo@codeaurora.org>,
        Hridya Valsaraju <hridya@google.com>,
        =?iso-8859-1?Q?=D8rjan?= Eide <orjan.eide@arm.com>,
        linux-media <linux-media@vger.kernel.org>,
        Suren Baghdasaryan <surenb@google.com>,
        Daniel Mentz <danielmentz@google.com>
References: <20201217230612.32397-1-john.stultz@linaro.org>
 <20201217230612.32397-2-john.stultz@linaro.org>
 <X9y+YZujWBTHMuH3@phenom.ffwll.local>
 <CALAqxLVtYVGSSYtFmMK6oM9JSEmY4RAXra89sECL2Z4YGPic0Q@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CALAqxLVtYVGSSYtFmMK6oM9JSEmY4RAXra89sECL2Z4YGPic0Q@mail.gmail.com>
Precedence: bulk

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@ffwll.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