linux-kernel - Re: page pools, was Re: [PATCH v9 1/5] drm: Add a sharable drm page-pool implementation

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Date:   Wed, 7 Jul 2021 12:42:40 -0700
From:   John Stultz <john.stultz@...aro.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     "Christian K??nig" <christian.koenig@....com>,
        lkml <linux-kernel@...r.kernel.org>,
        Daniel Vetter <daniel@...ll.ch>,
        Sumit Semwal <sumit.semwal@...aro.org>,
        Liam Mark <lmark@...eaurora.org>,
        Chris Goldsworthy <cgoldswo@...eaurora.org>,
        Laura Abbott <labbott@...nel.org>,
        Brian Starkey <Brian.Starkey@....com>,
        Hridya Valsaraju <hridya@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Sandeep Patil <sspatil@...gle.com>,
        Daniel Mentz <danielmentz@...gle.com>,
        "??rjan Eide" <orjan.eide@....com>,
        Robin Murphy <robin.murphy@....com>,
        Ezequiel Garcia <ezequiel@...labora.com>,
        Simon Ser <contact@...rsion.fr>,
        James Jones <jajones@...dia.com>,
        linux-media <linux-media@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Mel Gorman <mgorman@...e.de>, linux-mm <linux-mm@...ck.org>
Subject: Re: page pools, was Re: [PATCH v9 1/5] drm: Add a sharable drm
 page-pool implementation

On Wed, Jul 7, 2021 at 12:15 AM Christoph Hellwig <hch@...radead.org> wrote:
>
> On Wed, Jul 07, 2021 at 09:10:26AM +0200, Christian K??nig wrote:
> > Well, the original code all this is based on already had the comment that
> > this really belong into the page allocator.
> >
> > The key point is traditionally only GPUs used uncached and write-combined
> > memory in such large quantities that having a pool for them makes sense.
> >
> > Because of this we had this separately to reduce the complexity in the page
> > allocator to handle another set of complexity of allocation types.
> >
> > For the upside, for those use cases it means huge performance improvements
> > for those drivers. See the numbers John provided in the cover letter.
> >
> > But essentially at least I would be totally fine moving this into the page
> > allocator, but moving it outside of TTM already helps with this goal. So
> > this patch set is certainly a step into the right direction.
>
> Unless I'm badly misreading the patch and this series there is nothing
> about cache attributes in this code.  It just allocates pages, zeroes
> them, eventually hands them out to a consumer and registers a shrinker
> for its freelist.
>
> If OTOH it actually dealt with cachability that should be documented
> in the commit log and probably also the naming of the implementation.

So the cache attributes are still managed in the tmm_pool code. This
series just pulls the pool/shrinker management out into common code so
we can use it in the dmabuf heap code without duplicating things.

thanks
-john