linux-kernel - Re: [PATCH 6/9] readahead: clean up and simplify the code for filemap page fault readahead

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Date:	Mon, 13 Apr 2009 08:16:54 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	kosaki.motohiro@...fujitsu.com,
	Wu Fengguang <fengguang.wu@...el.com>,
	linux-kernel@...r.kernel.org, lpk@....spb.su,
	wli@...ementarian.org, torvalds@...ux-foundation.org,
	yinghan@...gle.com, Nick Piggin <npiggin@...e.de>,
	Hugh Dickins <hugh@...itas.com>, Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH 6/9] readahead: clean up and simplify the code for filemap  page fault readahead

> On Sat, 11 Apr 2009 22:58:31 +0900 KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com> wrote:
> 
> > > Ah. __But I have a note here that I didn't like it, because it adds lots
> > > of new spinlocking to fastpaths. __So I'll leave things as they stand
> > > until we have had a little talk about that.
> > 
> > add?
> > 
> > old code: grab zone->lru_lock via mark_page_accessed()
> > new code: grab zone->lru_lock via update_reclaim_stat()
> > 
> > one remove, one add.
> > 
> 
> mm-update_page_reclaim_stat-is-called-from-page-fault-path.patch adds
> new calls to update_page_reclaim_stat() into do_swap_page() and
> filemap_fault().  update_page_reclaim_stat() does spin_lock_irq() and
> spin_unlock_irq().  It looks like a net slowdown to me.

Ah, I compared with the code before Nick's mark_page_accessed() removing.
but you don't.

but I agree this patch reduce the worth of nick's work.
I have to improve more.

> > But I agree its lock can be removed maybe..
> 
> It would be nice to try to do something about it - every little bit
> counts.

Yes. I can't opoose it.




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