linux-kernel - Re: [PATCH] mm: cma: honor __GFP_ZERO flag in cma

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Message-ID: <20180613133913.GD20315@dhcp22.suse.cz>
Date:   Wed, 13 Jun 2018 15:39:13 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Marek Szyprowski <m.szyprowski@...sung.com>,
        Matthew Wilcox <willy@...radead.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Nazarewicz <mina86@...a86.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH] mm: cma: honor __GFP_ZERO flag in cma_alloc()

On Wed 13-06-18 05:55:46, Christoph Hellwig wrote:
> On Wed, Jun 13, 2018 at 02:40:00PM +0200, Marek Szyprowski wrote:
> > It is not only the matter of the spinlocks. GFP_ATOMIC is not supported 
> > by the
> > memory compaction code, which is used in alloc_contig_range(). Right, this
> > should be also noted in the documentation.
> 
> Documentation is good, asserts are better.  The code should reject any
> flag not explicitly supported, or even better have its own flags type
> with the few actually supported flags.

Agreed. Is the cma allocator used for anything other than GFP_KERNEL
btw.? If not then, shouldn't we simply drop the gfp argument altogether
rather than give users a false hope for differen gfp modes that are not
really supported and grow broken code?

-- 
Michal Hocko
SUSE Labs