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From: Miklos Szeredi <miklos@szeredi.hu>
To: akpm@linux-foundation.org
Cc: a.p.zijlstra@chello.nl, linux-kernel@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, linux-mm@kvack.org
Subject: [patch 1/6] mm: bdi: tweak task dirty penalty
Date: Tue, 29 Jan 2008 16:49:01 +0100	[thread overview]
Message-ID: <20080129154947.110268504@szeredi.hu> (raw)
In-Reply-To: <20080129154900.145303789@szeredi.hu>

[-- Attachment #1: bdi-task-dirty.patch --]
[-- Type: text/plain, Size: 1341 bytes --]

From: Peter Zijlstra <a.p.zijlstra@chello.nl>

Penalizing heavy dirtiers with 1/8-th the total dirty limit might be rather
excessive on large memory machines. Use sqrt to scale it sub-linearly.

Update the comment while we're there.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
---

Index: linux/mm/page-writeback.c
===================================================================
--- linux.orig/mm/page-writeback.c	2008-01-17 19:00:56.000000000 +0100
+++ linux/mm/page-writeback.c	2008-01-18 13:07:16.000000000 +0100
@@ -219,17 +219,21 @@ static inline void task_dirties_fraction
 }
 
 /*
- * scale the dirty limit
+ * Task specific dirty limit:
  *
- * task specific dirty limit:
+ *   dirty -= 8 * sqrt(dirty) * p_{t}
  *
- *   dirty -= (dirty/8) * p_{t}
+ * Penalize tasks that dirty a lot of pages by lowering their dirty limit. This
+ * avoids infrequent dirtiers from getting stuck in this other guys dirty
+ * pages.
+ *
+ * Use a sub-linear function to scale the penalty, we only need a little room.
  */
 static void task_dirty_limit(struct task_struct *tsk, long *pdirty)
 {
 	long numerator, denominator;
 	long dirty = *pdirty;
-	u64 inv = dirty >> 3;
+	u64 inv = 8*int_sqrt(dirty);
 
 	task_dirties_fraction(tsk, &numerator, &denominator);
 	inv *= numerator;

--

  reply	other threads:[~2008-01-29 15:52 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-01-29 15:49 [patch 0/6] mm: bdi: updates Miklos Szeredi
2008-01-29 15:49 ` Miklos Szeredi [this message]
2008-01-31  0:13   ` [patch 1/6] mm: bdi: tweak task dirty penalty Andrew Morton
2008-01-29 15:49 ` [patch 2/6] mm: bdi: export BDI attributes in sysfs Miklos Szeredi
2008-01-29 17:39   ` Greg KH
2008-01-31  0:28   ` Andrew Morton
2008-01-31  9:39     ` Miklos Szeredi
2008-01-31  9:54       ` Andrew Morton
2008-01-31 10:08         ` Peter Zijlstra
2008-02-29 11:26   ` Andrew Morton
2008-01-29 15:49 ` [patch 3/6] mm: bdi: expose the BDI object in sysfs for NFS Miklos Szeredi
2008-01-29 15:49 ` [patch 4/6] mm: bdi: expose the BDI object in sysfs for FUSE Miklos Szeredi
2008-01-29 15:49 ` [patch 5/6] mm: bdi: allow setting a minimum for the bdi dirty limit Miklos Szeredi
2008-01-29 15:49 ` [patch 6/6] mm: bdi: allow setting a maximum " Miklos Szeredi
2008-01-31  0:39   ` Andrew Morton
2008-01-31  9:46     ` Miklos Szeredi
2008-01-31 10:17       ` Peter Zijlstra
2008-01-29 17:06 ` [patch 0/6] mm: bdi: updates Peter Zijlstra
2008-01-29 18:32   ` Miklos Szeredi

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