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: <798f5d1d-b64c-8c73-bfe6-701893820ff0@amd.com>
Date:   Thu, 8 Jul 2021 09:37:41 +0200
From:   Christian König <christian.koenig@....com>
To:     Christoph Hellwig <hch@...radead.org>,
        John Stultz <john.stultz@...aro.org>
Cc:     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

Am 08.07.21 um 06:20 schrieb Christoph Hellwig:
> 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.

And I think functionality like that should be part of the common page 
allocator.

I mean we already have __GFP_ZERO, why not have a background kernel 
thread which zeros free pages when a CPU core is idle? (I'm pretty sure 
we already have that somehow).

Christian.