linux-kernel - Re: [PATCH 2/2] mm: Indicate pfmemalloc pages in compound

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Message-ID: <20210417212843.GT2531743@casper.infradead.org>
Date:   Sat, 17 Apr 2021 22:28:43 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     David Laight <David.Laight@...lab.com>
Cc:     "brouer@...hat.com" <brouer@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>,
        "ilias.apalodimas@...aro.org" <ilias.apalodimas@...aro.org>,
        "mcroce@...ux.microsoft.com" <mcroce@...ux.microsoft.com>,
        "grygorii.strashko@...com" <grygorii.strashko@...com>,
        "arnd@...nel.org" <arnd@...nel.org>, "hch@....de" <hch@....de>,
        "linux-snps-arc@...ts.infradead.org" 
        <linux-snps-arc@...ts.infradead.org>,
        "mhocko@...nel.org" <mhocko@...nel.org>,
        "mgorman@...e.de" <mgorman@...e.de>
Subject: Re: [PATCH 2/2] mm: Indicate pfmemalloc pages in compound_head

On Sat, Apr 17, 2021 at 09:13:45PM +0000, David Laight wrote:
> >  		struct {	/* page_pool used by netstack */
> > -			/**
> > -			 * @dma_addr: might require a 64-bit value on
> > -			 * 32-bit architectures.
> > -			 */
> > +			unsigned long pp_magic;
> > +			unsigned long xmi;
> > +			unsigned long _pp_mapping_pad;
> >  			unsigned long dma_addr[2];
> >  		};
> 
> You've deleted the comment.

Yes.  It no longer added any value.  You can see dma_addr now occupies
two words.

> I also think there should be a comment that dma_addr[0]
> must be aliased to ->index.

That's not a requirement.  Moving the pfmemalloc indicator is a
requirement so that we _can_ use index, but there's no requirement about
how index is used.