linux-kernel - Re: [PATCH 1/2] mm: introduce page reference manipulation functions

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Message-ID: <20151109114537.GA3903@node.shutemov.name>
Date:	Mon, 9 Nov 2015 13:45:37 +0200
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Joonsoo Kim <js1304@...il.com>
Cc:	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Nazarewicz <mina86@...a86.com>,
	Minchan Kim <minchan@...nel.org>, Mel Gorman <mgorman@...e.de>,
	Vlastimil Babka <vbabka@...e.cz>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Linux Memory Management List <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>, linux-api@...r.kernel.org,
	Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH 1/2] mm: introduce page reference manipulation functions

On Mon, Nov 09, 2015 at 05:00:32PM +0900, Joonsoo Kim wrote:
> 2015-11-09 16:53 GMT+09:00 Sergey Senozhatsky
> <sergey.senozhatsky.work@...il.com>:
> > Hi,
> >
> > On (11/09/15 16:23), Joonsoo Kim wrote:
> > [..]
> >> +static inline int page_count(struct page *page)
> >> +{
> >> +     return atomic_read(&compound_head(page)->_count);
> >> +}
> >> +
> >> +static inline void set_page_count(struct page *page, int v)
> >> +{
> >> +     atomic_set(&page->_count, v);
> >> +}
> >> +
> >> +/*
> >> + * Setup the page count before being freed into the page allocator for
> >> + * the first time (boot or memory hotplug)
> >> + */
> >> +static inline void init_page_count(struct page *page)
> >> +{
> >> +     set_page_count(page, 1);
> >> +}
> >> +
> >> +static inline void page_ref_add(struct page *page, int nr)
> >> +{
> >> +     atomic_add(nr, &page->_count);
> >> +}
> >
> > Since page_ref_FOO wrappers operate with page->_count and there
> > are already page_count()/set_page_count()/etc. may be name new
> > wrappers in page_count_FOO() manner?
> 
> Hello,
> 
> I used that page_count_ before but change my mind.
> I think that ref is more relevant to this operation.
> Perhaps, it'd be better to change page_count()/set_page_count()
> to page_ref()/set_page_ref().

What about get_page() vs. page_cache_get() and put_page() vs.
page_cache_release()? Two different helpers for the same thing is annyoing
me for some time (plus PAGE_SIZE vs. PAGE_CACHE_SIZE, etc.).

If you want coherent API you might want to get them consitent too.

> FYI, some functions such as page_(un)freeze_refs uses ref. :)

-- 
 Kirill A. Shutemov
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