linux-kernel - Re: [PATCH] Negative (setpoint-dirty) in bdi_position

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Message-ID: <20130124145707.GB12745@localhost>
Date:	Thu, 24 Jan 2013 22:57:07 +0800
From:	Fengguang Wu <fengguang.wu@...el.com>
To:	paul.szabo@...ney.edu.au
Cc:	linux-mm@...ck.org, 695182@...s.debian.org,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jan Kara <jack@...e.cz>
Subject: Re: [PATCH] Negative (setpoint-dirty) in bdi_position_ratio()

Hi Paul,

> (This patch does not solve the PAE OOM issue.)

You may try the below debug patch. The only way the writeback patches
should trigger OOM, I think, is for the number of dirty/writeback
pages going out of control.

Or more simple, you may show us the OOM dmesg which will contain the
number of dirty pages. Or run this in a continuous loop during your
tests, and see how the dirty numbers change before OOM:

while :
do
        grep -E '(Dirty|Writeback)' /proc/meminfo
        sleep 1
done

Thanks,
Fengguang

diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 50f0824..cf1165a 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1147,6 +1147,16 @@ pause:
 		if (task_ratelimit)
 			break;
 
+		if (nr_dirty > dirty_thresh + dirty_thresh / 2) {
+			if (printk_ratelimit())
+				printk(KERN_WARNING "nr_dirty=%lu dirty_thresh=%lu task_ratelimit=%lu dirty_ratelimit=%lu pos_ratio=%lu\n",
+				       nr_dirty,
+				       dirty_thresh,
+				       task_ratelimit,
+				       dirty_ratelimit,
+				       pos_ratio);
+		}
+
 		/*
 		 * In the case of an unresponding NFS server and the NFS dirty
 		 * pages exceeds dirty_thresh, give the other good bdi's a pipe
--
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