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

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Message-ID: <YOZ9JZlwkjyDGti5@infradead.org>
Date:   Thu, 8 Jul 2021 05:20:53 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     John Stultz <john.stultz@...aro.org>
Cc:     Christoph Hellwig <hch@...radead.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Daniel Vetter <daniel@...ll.ch>,
        Christian Koenig <christian.koenig@....com>,
        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 07, 2021 at 12:35:23PM -0700, John Stultz wrote:
> So, as Christian mentioned, on the TTM side it's useful, as they are
> trying to avoid TLB flushes when changing caching attributes.
> 
> For the dmabuf system heap purposes, the main benefit is moving the
> page zeroing to the free path, rather than the allocation path. This
> on its own doesn't save much, but allows us to defer frees (and thus
> the zeroing) to the background, which can get that work out of the hot
> path.

I really do no think that is worth it to fragment the free pages.