linux-kernel - Re: [RFC][PATCH v6 3/7] drm: ttm_pool: Rework ttm_pool_free_page to allow us to use it as a function pointer

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Date:   Tue, 9 Feb 2021 13:13:58 +0100
From:   Christian König <christian.koenig@....com>
To:     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>,
        Ørjan 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>
Subject: Re: [RFC][PATCH v6 3/7] drm: ttm_pool: Rework ttm_pool_free_page to
 allow us to use it as a function pointer



Am 05.02.21 um 20:47 schrieb John Stultz:
> On Fri, Feb 5, 2021 at 12:28 AM Christian König
> <christian.koenig@....com> wrote:
>> Am 05.02.21 um 09:06 schrieb John Stultz:
>>> This refactors ttm_pool_free_page(), and by adding extra entries
>>> to ttm_pool_page_dat, we then use it for all allocations, which
>>> allows us to simplify the arguments needed to be passed to
>>> ttm_pool_free_page().
>> This is a clear NAK since the peer page data is just a workaround for
>> the DMA-API hack to grab pages from there.
>>
>> Adding this to all pages would increase the memory footprint drastically.
> Yea, that's a good point!  Hrm... bummer. I'll have to see if there's
> some other way I can get the needed context for the free from the
> generic page-pool side.

What exactly is the problem here? As far as I can see we just have the 
lru entry (list_head) and the pool.

How the lru is cast to the page can be completely pool implementation 
specific.

Regards,
Christian.

>
> Thanks so much for the review!
> -john