linux-kernel - Re: Why kmem_cache_free occupy CPU for more than 10 seconds?

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Message-Id: <1176363565.6893.73.camel@twins>
Date:	Thu, 12 Apr 2007 09:39:25 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Zhao Forrest <forrest.zhao@...il.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: Why kmem_cache_free occupy CPU for more than 10 seconds?

On Wed, 2007-04-11 at 15:30 -0700, Andrew Morton wrote:

> There used to be a cond_resched() in invalidate_mapping_pages() which would
> have prevented this, but I rudely removed it to support
> /proc/sys/vm/drop_caches (which needs to call invalidate_inode_pages()
> under spinlock).
> 
> We could resurrect that cond_resched() by passing in some flag, I guess. 
> Or change the code to poke the softlockup detector.  The former would be
> better.

cond_resched() is conditional on __resched_legal(0), which should take
care of being called under a spinlock.

so I guess we can just reinstate the call in invalidate_mapping_pages()

(still waiting on the compile to finish...)
---
invalidate_mapping_pages() is called under locks (usually preemptable)
but can do a _lot_ of work, stick in a voluntary preemption point to
avoid excessive latencies (over 10 seconds was reported by softlockup).

Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
---
 mm/truncate.c |    2 ++
 1 file changed, 2 insertions(+)

Index: linux-2.6-mm/mm/truncate.c
===================================================================
--- linux-2.6-mm.orig/mm/truncate.c
+++ linux-2.6-mm/mm/truncate.c
@@ -292,6 +292,8 @@ unsigned long invalidate_mapping_pages(s
 			pgoff_t index;
 			int lock_failed;
 
+			cond_resched();
+
 			lock_failed = TestSetPageLocked(page);
 
 			/*


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