linux-kernel - Re: [PATCH v4 3/3] mm/page_alloc.c: do not warn allocation failure on zone DMA if no managed pages

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Message-ID: <20211227083253.GA24172@MiWiFi-R3L-srv>
Date:   Mon, 27 Dec 2021 16:32:53 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Hyeonggon Yoo <42.hyeyoo@...il.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org, hch@....de, cl@...ux.com,
        John.p.donnelly@...cle.com, kexec@...ts.infradead.org,
        penberg@...nel.org, rientjes@...gle.com, iamjoonsoo.kim@....com,
        vbabka@...e.cz, David.Laight@...lab.com, david@...hat.com,
        x86@...nel.org, bp@...en8.de
Subject: Re: [PATCH v4 3/3] mm/page_alloc.c: do not warn allocation failure
 on zone DMA if no managed pages

On 12/25/21 at 05:53am, Hyeonggon Yoo wrote:
> On Thu, Dec 23, 2021 at 05:44:35PM +0800, Baoquan He wrote:
...... 
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index 7c7a0b5de2ff..843bc8e5550a 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -4204,7 +4204,8 @@ void warn_alloc(gfp_t gfp_mask, nodemask_t *nodemask, const char *fmt, ...)
> >  	va_list args;
> >  	static DEFINE_RATELIMIT_STATE(nopage_rs, 10*HZ, 1);
> >  
> > -	if ((gfp_mask & __GFP_NOWARN) || !__ratelimit(&nopage_rs))
> > +	if ((gfp_mask & __GFP_NOWARN) || !__ratelimit(&nopage_rs) ||
> > +		(gfp_mask & __GFP_DMA) && !has_managed_dma())
> >  		return;
> >
> 
> Warning when there's always no page in DMA zone is unnecessary 
> and it confuses user.
> 
> The patch looks good.
> Reviewed-by: Hyeonggon Yoo <42.hyeyoo@...il.com>
> 
> And there is some driers that allocate memory with GFP_DMA
> even if that flag is unnecessary. We need to do cleanup later.

Thanks for reviewing and giving out some awesome suggestions.

> 
> Baoquan Are you planning to do it soon?
> I want to help that.

Yes, I had the plan and have done a little part. I talked to Christoph
about my thought. I planned to collect all kmalloc(GFP_DMA) callsite and
post a RFC mail, CC mailing list and maintainers related. Anyone
interested or know one or several callsites well can help.

Now, Christoph has handled all under drviers/scsi, and post patches to
fix them. I have gone throug those places and found out below callsites
where we can remove GFP_DMA directly when calling kmalloc() since not
necessary. And even found one place kmalloc(GFP_DMA32).

(HEAD -> master) vxge: don't use GFP_DMA
mtd: rawnand: marvell: don't use GFP_DMA
HID: intel-ish-hid: remove wrong GFP_DMA32 flag
ps3disk: don't use GFP_DMA
atm: iphase: don't use GFP_DMA

Next, I will send a RFC mail to contain those suspect callsites. We can
track them and can help if needed. Suggest to change them with:
1) using dma_alloc_xx , or dma_map_xx after kmalloc()
2) using alloc_pages(GFP_DMA) instead

When we fix, we all post patch with subject key words as
'xxxx: don't use GFP_DMA'. Christoph has posted patch with the similar
subject, we can search subject to get all related patches for later back
porting.

I will add you to CC when sending. Could be tomorrow. Any suggestion or thought?

Thanks
Baoquan