linux-kernel - Re: [PATCH RESEND v2 2/5] dma-pool: allow user to disable atomic pool

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Date:   Mon, 13 Dec 2021 16:16:41 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Christoph Hellwig <hch@....de>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, robin.murphy@....com, cl@...ux.com,
        penberg@...nel.org, rientjes@...gle.com, iamjoonsoo.kim@....com,
        vbabka@...e.cz, m.szyprowski@...sung.com,
        John.p.donnelly@...cle.com, kexec@...ts.infradead.org
Subject: Re: [PATCH RESEND v2 2/5] dma-pool: allow user to disable atomic pool

On 12/13/21 at 08:44am, Christoph Hellwig wrote:
> On Tue, Dec 07, 2021 at 11:07:47AM +0800, Baoquan He wrote:
> > In the current code, three atomic memory pools are always created,
> > atomic_pool_kernel|dma|dma32, even though 'coherent_pool=0' is
> > specified in kernel command line. In fact, atomic pool is only
> > necessary when CONFIG_DMA_DIRECT_REMAP=y or mem_encrypt_active=y
> > which are needed on few ARCHes.
> 
> And only these select the atomic pool, so it won't get created otherwise.
> What problem are you trying to solve?

This tries to make "coherent_pool=0" behave normally. As you see,
'coherent_pool=0' will behave like no 'coherent_pool' being specified.
This is not consistent with other similar kernel parameter, e.g cma=.

At the beginning, I planned to add a knob to allow user to disable one
or all atomic pool. Later I changed. However I think this patch makes
sense on fixing the a little bizarre behaviour, 'coherent_pool=0' but
still get atomic pool created.

I can drop it if you think it's unnecessary.