linux-kernel - Re: [patch 4/9] mm + fs: prepare for non-page entries in page cache radix trees

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Message-Id: <20130820135910.6e6da048131bc841404906be@linux-foundation.org>
Date:	Tue, 20 Aug 2013 13:59:10 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Greg Thelen <gthelen@...gle.com>,
	Christoph Hellwig <hch@...radead.org>,
	Hugh Dickins <hughd@...gle.com>, Jan Kara <jack@...e.cz>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Mel Gorman <mgorman@...e.de>,
	Minchan Kim <minchan.kim@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Rik van Riel <riel@...hat.com>,
	Michel Lespinasse <walken@...gle.com>,
	Seth Jennings <sjenning@...ux.vnet.ibm.com>,
	Roman Gushchin <klamm@...dex-team.ru>,
	Ozgun Erdogan <ozgun@...usdata.com>,
	Metin Doslu <metin@...usdata.com>,
	Vlastimil Babka <vbabka@...e.cz>, linux-mm@...ck.org,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 4/9] mm + fs: prepare for non-page entries in page cache
 radix trees

On Sat, 17 Aug 2013 15:31:18 -0400 Johannes Weiner <hannes@...xchg.org> wrote:

> shmem mappings already contain exceptional entries where swap slot
> information is remembered.
> 
> To be able to store eviction information for regular page cache,
> prepare every site dealing with the radix trees directly to handle
> entries other than pages.
> 
> The common lookup functions will filter out non-page entries and
> return NULL for page cache holes, just as before.  But provide a raw
> version of the API which returns non-page entries as well, and switch
> shmem over to use it.
> 
>
> ...
>
> -/**
> - * find_get_page - find and get a page reference
> - * @mapping: the address_space to search
> - * @offset: the page index
> - *
> - * Is there a pagecache struct page at the given (mapping, offset) tuple?
> - * If yes, increment its refcount and return it; if no, return NULL.
> - */
> -struct page *find_get_page(struct address_space *mapping, pgoff_t offset)
> +struct page *__find_get_page(struct address_space *mapping, pgoff_t offset)
>  {
>  	void **pagep;
>  	struct page *page;
> @@ -812,24 +828,31 @@ out:
>  
>  	return page;
>  }
> -EXPORT_SYMBOL(find_get_page);
> +EXPORT_SYMBOL(__find_get_page);

Deleting the interface documentation for a global, exported-to-modules
function was a bit rude.

And it does need documentation, to tell people that it can return the
non-pages.

Does it have the same handling of non-pages as __find_get_pages()?  It
had better, given the naming!

>
> ...
>
--
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