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Date:   Thu, 11 Aug 2022 09:34:54 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Michal Hocko <mhocko@suse.com>
Cc:     Baoquan He <bhe@redhat.com>, Christoph Hellwig <hch@lst.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        John Donnelly <john.p.donnelly@oracle.com>,
        David Hildenbrand <david@redhat.com>, linux-mm@kvack.org,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] dma/pool: do not complain if DMA pool is not allocated
Message-ID: <20220811073454.GD13886@lst.de>
References: <Yj3zyLs4f+ba6UqF@dhcp22.suse.cz> <YupFSpXOrcfXJNya@dhcp22.suse.cz> <YuqNToCACD8kKBG+@MiWiFi-R3L-srv> <YuqOrJKcgfamdXkk@dhcp22.suse.cz> <YuqU87SDwP0zg+c7@MiWiFi-R3L-srv> <YuqX0OAItlMDfRUV@dhcp22.suse.cz> <YuunCO2lsLDWTGw+@MiWiFi-R3L-srv> <Yuu1EyC95XL98XNI@dhcp22.suse.cz> <Yu0OWLbzLxCkSGVJ@MiWiFi-R3L-srv> <Yu1VTAxd9/jP/iEk@dhcp22.suse.cz>
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On Fri, Aug 05, 2022 at 07:37:16PM +0200, Michal Hocko wrote:
> GFP_DMA is a misnomer. It doesn't really say that the allocation should
> be done for actual DMA. GFP_DMA really says allocate from ZONE_DMA.

Yes.  But in practice that either is to do DMA of some form, including
the s390 variant not using the dma api, or completely stupid cargo
cult code.

> It
> is my understanding that all actual DMA users should use a dedicated dma
> allocation APIs which should do the right thing wrt. address constrains.

Yes.  And we were at a point where we got to that, but it seems somewhat
recently a lot of people added completely stupid GFP_DMA kmallocs in the
all over the crypto drivers.  Sigh...