linux-kernel - Re: [PATCH 1/2] mm,mlock: drain pagevecs asynchronously

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Date:	Wed, 04 Jan 2012 18:33:12 -0500
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	David Rientjes <rientjes@...gle.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Mel Gorman <mel@....ul.ie>,
	Johannes Weiner <jweiner@...hat.com>
Subject: Re: [PATCH 1/2] mm,mlock: drain pagevecs asynchronously

(1/4/12 5:05 PM), Andrew Morton wrote:
> On Sun,  1 Jan 2012 02:30:24 -0500
> kosaki.motohiro@...il.com wrote:
>
>> Because lru_add_drain_all() spent much time.
>
> Those LRU pagevecs are horrid things.  They add high code and
> conceptual complexity, they add pointless uniprocessor overhead and the
> way in which they leave LRU pages floating around not on an LRU is
> rather maddening.
>
> So the best way to fix all of this as well as this problem we're
> observing is, I hope, to completely remove them.
>
> They've been in there for ~10 years and at the time they were quite
> beneficial in reducing lru_lock contention, hold times, acquisition
> frequency, etc.
>
> The approach to take here is to prepare the patches which eliminate
> lru_*_pvecs then identify the problems which occur as a result, via
> code inspection and runtime testing.  Then fix those up.
>
> Many sites which take lru_lock are already batching the operation.
> It's a matter of hunting down those sites which take the lock
> once-per-page and, if they have high frequency, batch them up.
>
> Converting readahead to batch the locking will be pretty simple
> (read_pages(), mpage_readpages(), others).  That will fix pagefaults
> too.
>
> rotate_reclaimable_page() can be batched by batching
> end_page_writeback(): a bio contains many pages already.
>
> deactivate_page() can be batched too - invalidate_mapping_pages() is
> already working on large chunks of pages.
>
> Those three cases are fairly simple - we just didn't try, because the
> lru_*_pvecs were there to do the work for us.

got it. so, let's wait hugh's "mm: take pagevecs off reclaim stack" next spin
and make the patches on top of it.


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