linux-kernel - Re: [PATCH v2] page cache: Store only head pages in i

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Message-ID: <20190214221158.GF12668@bombadil.infradead.org>
Date:   Thu, 14 Feb 2019 14:11:58 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org, Hugh Dickins <hughd@...gle.com>,
        William Kucharski <william.kucharski@...cle.com>
Subject: Re: [PATCH v2] page cache: Store only head pages in i_pages

On Fri, Feb 15, 2019 at 01:08:10AM +0300, Kirill A. Shutemov wrote:
> On Thu, Feb 14, 2019 at 01:17:57PM -0800, Matthew Wilcox wrote:
> > On Thu, Feb 14, 2019 at 04:30:04PM +0300, Kirill A. Shutemov wrote:
> > >  - migrate_page_move_mapping() has to be converted too.
> > 
> > I think that's as simple as:
> > 
> > +++ b/mm/migrate.c
> > @@ -465,7 +465,7 @@ int migrate_page_move_mapping(struct address_space *mapping,
> >  
> >                 for (i = 1; i < HPAGE_PMD_NR; i++) {
> >                         xas_next(&xas);
> > -                       xas_store(&xas, newpage + i);
> > +                       xas_store(&xas, newpage);
> >                 }
> >         }
> >  
> > 
> > or do you see something else I missed?
> 
> Looks right to me.
> 
> BTW, maybe some add syntax sugar from XArray side?
> 
> Replace the loop and xas_store() before it with:
> 
> 		xas_fill(&xas, newpage, 1UL << compound_order(newpage));
> 
> or something similar?

If we were keeping this code longterm, then yes, something like that
would be great.  I'm hoping this code is a mere stepping stone towards
using multi-slot entries for the page cache.