linux-kernel - Re: [PATCH net-next v7 1/5] mm: add a signature in struct page

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Message-ID: <CAFnufp1fF5NtM_NzhVG6MmRwkvDot+usPdAOhHdfQUVCHhV75w@mail.gmail.com>
Date:   Mon, 7 Jun 2021 15:58:23 +0200
From:   Matteo Croce <mcroce@...ux.microsoft.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     netdev@...r.kernel.org, linux-mm@...ck.org,
        Ayush Sawal <ayush.sawal@...lsio.com>,
        Vinay Kumar Yadav <vinay.yadav@...lsio.com>,
        Rohit Maheshwari <rohitm@...lsio.com>,
        "David S. Miller" <davem@...emloft.net>,
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        Tariq Toukan <tariqt@...dia.com>,
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        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
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        Andrew Lunn <andrew@...n.ch>, Paolo Abeni <pabeni@...hat.com>,
        Sven Auhagen <sven.auhagen@...eatech.de>
Subject: Re: [PATCH net-next v7 1/5] mm: add a signature in struct page

On Mon, Jun 7, 2021 at 3:53 PM Matthew Wilcox <willy@...radead.org> wrote:
>
> On Sun, Jun 06, 2021 at 03:50:54AM +0200, Matteo Croce wrote:
> > And change all the *_pfmemalloc functions to use page->lru.next like this?
> >
> > @@ -1668,10 +1668,12 @@ struct address_space *page_mapping(struct page *page);
> > static inline bool page_is_pfmemalloc(const struct page *page)
> > {
> >        /*
> > -        * Page index cannot be this large so this must be
> > -        * a pfmemalloc page.
> > +        * This is not a tail page; compound_head of a head page is unused
> > +        * at return from the page allocator, and will be overwritten
> > +        * by callers who do not care whether the page came from the
> > +        * reserves.
> >         */
>
> The comment doesn't make a lot of sense if we're switching to use
> lru.next.  How about:
>
>         /*
>          * lru.next has bit 1 set if the page is allocated from the
>          * pfmemalloc reserves.  Callers may simply overwrite it if
>          * they do not need to preserve that information.
>          */

Sounds good!

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