linux-kernel - Re: [PATCH] mm/mm_init.c: add debug messsge for dma zone

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Date:   Thu, 8 Jun 2023 13:13:40 +0300
From:   Mike Rapoport <rppt@...nel.org>
To:     Michal Hocko <mhocko@...e.com>
Cc:     Haifeng Xu <haifeng.xu@...pee.com>,
        David Hildenbrand <david@...hat.com>,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/mm_init.c: add debug messsge for dma zone

On Thu, Jun 08, 2023 at 11:18:02AM +0200, Michal Hocko wrote:
> On Thu 08-06-23 15:38:48, Haifeng Xu wrote:
> > 
> > 
> > On 2023/6/7 18:22, David Hildenbrand wrote:
> > > On 07.06.23 12:16, Michal Hocko wrote:
> > >> On Wed 07-06-23 09:07:34, Haifeng Xu wrote:
> > >>> If freesize is less than dma_reserve, print warning message to report
> > >>> this case.
> > >>
> > >> Why?
> > > 
> > > I'd like to second that question, and add
> > > 
> > > a) Did you run into that scenario?
> > > b) What can an admin do in that case with that error messages?
> > 
> > In theory，dma_reserve shouldn't exceed freesize, so the error messages can remind us
> > to verify whether the configuration of reserved memory is correct.
> 
> I am not really convinced this is worth touching the code TBH.

The only architecture that sets the dma_reserve is x86_64 and it sets it to
the number of reserved pages in DMA zone. There is no way freesize will be
less than dma_reserve.

I'm not sure that in general dma_reserve has some value now, but that's a
completely different story.

> -- 
> Michal Hocko
> SUSE Labs

-- 
Sincerely yours,
Mike.