Re: Extending page pinning into fs/direct-io.c

From: David Howells <dhowells@redhat.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: dhowells@redhat.com, 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
Subject: Re: Extending page pinning into fs/direct-io.c
Date: Thu, 25 May 2023 18:15:15 +0100	[thread overview]
Message-ID: <144598.1685034915@warthog.procyon.org.uk> (raw)
In-Reply-To: <CAHk-=wgPWUCyhiM+=S3nmh4JK8qtBQteYvtiXpoYpDjfKHnEhQ@mail.gmail.com>

Linus Torvalds <torvalds@linux-foundation.org> wrote:

> So I suspect we should add that
> 
>     is_zero_pfn(page_to_pfn(page))
> 
> as a helper inline function rather than write it out even more times
> (that "is this 'struct page' a zero page" pattern already exists in
> /proc and a few other places.
> 
> is_longterm_pinnable_page() already has it, so adding it as a helper
> there in <linux/mm.h> is probably a good idea.

I just added:

static inline bool IS_ZERO_PAGE(const struct page *page)
{
	return is_zero_pfn(page_to_pfn(page));
}

static inline bool IS_ZERO_FOLIO(const struct folio *folio)
{
	return is_zero_pfn(page_to_pfn((const struct page *)folio));
}

to include/linux/pgtable.h.  It doesn't seem I can add it to mm.h as an inline
function.

David