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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Thu, 25 May 2023 10:25:42 -0700
Message-ID: <CAHk-=wirrJNoVSOSVK2ae9pa7Q5kJKFYMk2ad-_6YrS1cEScqA@mail.gmail.com>
Subject: Re: Extending page pinning into fs/direct-io.c
To:     David Howells <dhowells@redhat.com>
Cc:     David Hildenbrand <david@redhat.com>,
        Christoph Hellwig <hch@infradead.org>,
        Jens Axboe <axboe@kernel.dk>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Matthew Wilcox <willy@infradead.org>, Jan Kara <jack@suse.cz>,
        Jeff Layton <jlayton@kernel.org>,
        Jason Gunthorpe <jgg@nvidia.com>,
        Logan Gunthorpe <logang@deltatee.com>,
        Hillf Danton <hdanton@sina.com>,
        Christian Brauner <brauner@kernel.org>,
        linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-mm@kvack.org
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On Thu, May 25, 2023 at 10:15=E2=80=AFAM David Howells <dhowells@redhat.com=
> wrote:
>
>  It doesn't seem I can add it to mm.h as an inline function.

What? We already have that pattern inside is_longterm_pinnable_page(),
so that's really strange.

But regardless, please don't duplicate that odd conditional for no
reason, and don't scream.

So regardless of where it is, make that "is_zero_folio()" just do
"is_zero_page(&folio->page)" rather than repeat the question.

I also wonder whether we shouldn't just use the "transparent union"
argument thing more aggressively. Something like

   typedef union {
        struct page *page;
        struct folio *folio;
   } page_or_folio_t __attribute__ ((__transparent_union__));

and then you should be able to do something like this:

    static inline bool is_zero_page(const page_or_folio_t arg)
    {
        return is_zero_pfn(page_to_pfn(arg.page));
    }

and we don't have to keep generating the two versions over and over
and over again.

                Linus