linux-kernel - Re: [patch 3/3] mm: keep pages from unevictable mappings off the LRU lists

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Date:	Mon, 23 Mar 2009 11:21:36 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Minchan Kim <minchan.kim@...il.com>
Cc:	kosaki.motohiro@...fujitsu.com,
	Johannes Weiner <hannes@...xchg.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	David Howells <dhowells@...hat.com>,
	Nick Piggin <npiggin@...e.de>, Rik van Riel <riel@...hat.com>,
	Peter Zijlstra <peterz@...radead.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>
Subject: Re: [patch 3/3] mm: keep pages from unevictable mappings off the LRU  lists

> Hmm,,
> 
> This patch is another thing unlike previous series patches.
> Firstly, It looked good to me.
> 
> I think add_to_page_cache_lru have to become a fast path.
> But, how often would ramfs and shmem function be called ?
> 
> I have a concern for this patch to add another burden.
> so, we need any numbers for getting pros and cons.
> 
> Any thoughts ?

this is the just reason why current code don't call add_page_to_unevictable_list().
add_page_to_unevictable_list() don't use pagevec. it is needed for avoiding race.

then, if readahead path (i.e. add_to_page_cache_lru()) use add_page_to_unevictable_list(),
it can cause zone->lru_lock contention storm.

then, if nobody have good performance result, I don't ack this patch.


> On Mon, Mar 23, 2009 at 5:13 AM, Johannes Weiner <hannes@...xchg.org> wrote:
> > Check if the mapping is evictable when initially adding page cache
> > pages to the LRU lists. ?If that is not the case, add them to the
> > unevictable list immediately instead of leaving it up to the reclaim
> > code to move them there.
> >
> > This is useful for ramfs and locked shmem which mark whole mappings as
> > unevictable and we know at fault time already that it is useless to
> > try reclaiming these pages.


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