linux-ext4 - Re: [PATCH 1/3] mm: pagevec: Defer deciding what LRU to add a page to until pagevec drain time

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Date:	Fri, 3 May 2013 09:37:49 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Jan Kara <jack@...e.cz>
Cc:	Alexey Lyahkov <alexey.lyashkov@...il.com>,
	Andrew Perepechko <anserper@...ru>,
	Robin Dong <sanbai@...bao.com>, Theodore Tso <tytso@....edu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Hugh Dickins <hughd@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Bernd Schubert <bernd.schubert@...tmail.fm>,
	David Howells <dhowells@...hat.com>,
	Trond Myklebust <Trond.Myklebust@...app.com>,
	Linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Linux-ext4 <linux-ext4@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux-mm <linux-mm@...ck.org>
Subject: Re: [PATCH 1/3] mm: pagevec: Defer deciding what LRU to add a page
 to until pagevec drain time

On Fri, May 03, 2013 at 09:51:58AM +0200, Jan Kara wrote:
> > @@ -789,17 +787,16 @@ void lru_add_page_tail(struct page *page, struct page *page_tail,
> >  static void __pagevec_lru_add_fn(struct page *page, struct lruvec *lruvec,
> >  				 void *arg)
> >  {
> > -	enum lru_list lru = (enum lru_list)arg;
> > -	int file = is_file_lru(lru);
> > -	int active = is_active_lru(lru);
> > +	enum lru_list requested_lru = (enum lru_list)arg;
> > +	int file = page_is_file_cache(page);
> > +	int active = PageActive(page);
> > +	enum lru_list lru = page_lru(page);
> >  
> > -	VM_BUG_ON(PageActive(page));
> > +	WARN_ON_ONCE(requested_lru < NR_LRU_LISTS && requested_lru != lru);
>   Hum, so __lru_cache_add() calls this with 'requested_lru' set to whatever
> LRU we currently want to add a page. How should this always be equal to the
> LRU of all the pages we have cached in the pagevec?
> 

It wouldn't necessarily be and and for a pagevec drain, it's ignored
completely.

> And if I'm right, there doesn't seem to be a reason to pass requested_lru
> to this function at all, does it?
> 

You've already noticed that it gets thrown away later in the third
patch. It was left in this patch as a debugging aid in case there was a
direct pagevec user that expected to place pages on an LRU that was at
odds with the page flags.

-- 
Mel Gorman
SUSE Labs
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