linux-kernel - Re: [PATCH 5/5] mm: remove unlikelys for unlock in rmap.c

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Date:	Fri, 24 Apr 2009 08:15:43 -0400
From:	Lee Schermerhorn <Lee.Schermerhorn@...com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Roland McGrath <roland@...hat.com>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Steven Rostedt <srostedt@...hat.com>,
	Hugh Dickins <hugh@...itas.com>
Subject: Re: [PATCH 5/5] mm: remove unlikelys for unlock in rmap.c

On Fri, 2009-04-24 at 20:12 +0900, KOSAKI Motohiro wrote:
> (cc to lee)
> 
> > From: Steven Rostedt <rostedt@...dmis.org>
> > 
> > Impact: clean up
> > 
> > The annotated branch profiler shows that the rmap calls are likely
> > called with unlock set.
> > 
> >  correct incorrect  %        Function                  File              Line
> >  ------- ---------  -        --------                  ----              ----
> >        0    46100 100 try_to_unmap_anon              rmap.c               1013
> >        0    46100 100 try_to_unmap_anon              rmap.c               1005
> >        0     5763 100 try_to_unmap_file              rmap.c               1074
> >        0     5763 100 try_to_unmap_file              rmap.c               1069
> > 
> > Signed-off-by: Steven Rostedt <srostedt@...hat.com>
> 
> unlock==1 mean munlock() is called.
> unlock==0 mean memory shortage and reclaim happend.
> 
> So, we did guess end-user don't use munlock() so frequently.
> but reclaim is frequently happend.
> 
> Oh well, but you have rich machine. hmm...
> ok, I can agree user can use munlock() frequently.
> 
> 
> 	Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
> 

In current mainline, try_to_munlock() is called only from
munlock_vma_page() and then only when page is actually mlocked.  So, you
should only see the profile above during a test that is munlock()ing a
lot of pages.  However, after try_to_munlock() was introduced, we'd
added a call to it in vmscan.c to test for mlocked anon pages to avoid
allocating swap to mlocked pages.  At the time, we couldn't reliably
free swap there.  Hugh fixed this and removed the call from vmscan.  If
Steve was testing a kernel before the call was removed, he would have
seen the calls when reclaiming any anon pages.

Steve:  what test were you using and on what version?

Regards,
Lee

> 
> 
> 
> > ---
> >  mm/rmap.c |    8 ++++----
> >  1 files changed, 4 insertions(+), 4 deletions(-)
> > 
> > diff --git a/mm/rmap.c b/mm/rmap.c
> > index 1652166..ad62fe0 100644
> > --- a/mm/rmap.c
> > +++ b/mm/rmap.c
> > @@ -1002,7 +1002,7 @@ static int try_to_unmap_anon(struct page *page, int unlock, int migration)
> >  	unsigned int mlocked = 0;
> >  	int ret = SWAP_AGAIN;
> >  
> > -	if (MLOCK_PAGES && unlikely(unlock))
> > +	if (MLOCK_PAGES && unlock)
> >  		ret = SWAP_SUCCESS;	/* default for try_to_munlock() */
> >  
> >  	anon_vma = page_lock_anon_vma(page);
> > @@ -1010,7 +1010,7 @@ static int try_to_unmap_anon(struct page *page, int unlock, int migration)
> >  		return ret;
> >  
> >  	list_for_each_entry(vma, &anon_vma->head, anon_vma_node) {
> > -		if (MLOCK_PAGES && unlikely(unlock)) {
> > +		if (MLOCK_PAGES && unlock) {
> >  			if (!((vma->vm_flags & VM_LOCKED) &&
> >  			      page_mapped_in_vma(page, vma)))
> >  				continue;  /* must visit all unlocked vmas */
> > @@ -1066,12 +1066,12 @@ static int try_to_unmap_file(struct page *page, int unlock, int migration)
> >  	unsigned int mapcount;
> >  	unsigned int mlocked = 0;
> >  
> > -	if (MLOCK_PAGES && unlikely(unlock))
> > +	if (MLOCK_PAGES && unlock)
> >  		ret = SWAP_SUCCESS;	/* default for try_to_munlock() */
> >  
> >  	spin_lock(&mapping->i_mmap_lock);
> >  	vma_prio_tree_foreach(vma, &iter, &mapping->i_mmap, pgoff, pgoff) {
> > -		if (MLOCK_PAGES && unlikely(unlock)) {
> > +		if (MLOCK_PAGES && unlock) {
> >  			if (!((vma->vm_flags & VM_LOCKED) &&
> >  						page_mapped_in_vma(page, vma)))
> >  				continue;	/* must visit all vmas */
> > -- 
> > 1.6.2
> > 
> > -- 
> > --
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> 
> 

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