linux-kernel - Re: [PATCH] dma/pool: do not complain if DMA pool is not allocated

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Message-ID: <20220325164856.GA16800@lst.de>
Date:   Fri, 25 Mar 2022 17:48:56 +0100
From:   Christoph Hellwig <hch@....de>
To:     Michal Hocko <mhocko@...e.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Hellwig <hch@....de>, Baoquan He <bhe@...hat.com>,
        John Donnelly <john.p.donnelly@...cle.com>,
        David Hildenbrand <david@...hat.com>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] dma/pool: do not complain if DMA pool is not allocated

On Fri, Mar 25, 2022 at 01:58:42PM +0100, Michal Hocko wrote:
> Dang, I have just realized that I have misread the boot log and it has
> turned out that a674e48c5443 is covering my situation because the
> allocation failure message says:
>
> Node 0 DMA free:0kB boost:0kB min:0kB low:0kB high:0kB reserved_highatomic:0KB active_anon:0kB inactive_anon:0kB active_file:0kB inactive_file:0kB unevictable:0kB writepending:0kB present:636kB managed:0kB mlocked:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB

As in your report is from a kernel that does not have a674e48c5443
yet?

> 
> I thought there are only few pages in the managed by the DMA zone. This
> is still theoretically possible so I think __GFP_NOWARN makes sense here
> but it would require to change the patch description.
> 
> Is this really worth it?

In general I think for kernels where we need the pool and can't allocate
it, a warning is very useful.  We just shouldn't spew it when there is
no need for the pool to start with.