netdev - Re: [PATCH 7/7] dma-mapping: reject __GFP_COMP in dma_alloc

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Message-ID: <Y3SNDR7KMJOkTREK@unreal>
Date:   Wed, 16 Nov 2022 09:11:09 +0200
From:   Leon Romanovsky <leon@...nel.org>
To:     Christoph Hellwig <hch@....de>
Cc:     Dennis Dalessandro <dennis.dalessandro@...nelisnetworks.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Alexandra Winter <wintera@...ux.ibm.com>,
        Wenjia Zhang <wenjia@...ux.ibm.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Russell King <linux@...linux.org.uk>,
        Robin Murphy <robin.murphy@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-rdma@...r.kernel.org,
        iommu@...ts.linux.dev, linux-media@...r.kernel.org,
        netdev@...r.kernel.org, linux-s390@...r.kernel.org,
        alsa-devel@...a-project.org
Subject: Re: [PATCH 7/7] dma-mapping: reject __GFP_COMP in dma_alloc_attrs

On Wed, Nov 16, 2022 at 07:11:06AM +0100, Christoph Hellwig wrote:
> On Mon, Nov 14, 2022 at 10:11:50AM +0200, Leon Romanovsky wrote:
> > In RDMA patches, you wrote that GFP_USER is not legal flag either. So it
> > is better to WARN here for everything that is not allowed.
> 
> So __GFP_COMP is actually problematic and changes behavior, and I plan
> to lift an optimization from the arm code to the generic one that
> only rounds up allocations to the next page size instead of the next
> power of two, so I need this check now.  Other flags including
> GFP_USER are pretty bogus to, but I actually need to do a full audit
> before rejecting them, which I've only done for GFP_COMP so far.

ok, let's do it later.

Thanks