linux-kernel - Re: Slow, persistent memory leak in 2.6.20

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Date:	Sun, 26 Aug 2007 12:16:21 -0400
From:	"Fred Tyler" <fredty8@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: Re: Slow, persistent memory leak in 2.6.20

On 8/26/07, Jan Engelhardt <jengelh@...putergmbh.de> wrote:
>
> On Aug 26 2007 11:51, Fred Tyler wrote:
> >On 8/26/07, Fred Tyler <fredty8@...il.com> wrote:
> >> I think I've come across a memory leak in 2.6.20. I've upgraded to the
> >> latest 2.6.20.17, but it didn't seem to help.
> >
> >Sorry to keep replying to my own post, but further investigation
> >suggests that the memory losses may be occurring at times of heavy
> >filesystem access. The machines in question run rsyncs of hundreds of
> >thousands of files every few hours, and I'm starting to think that the
> >memory loss occurs during these times. I don't know how I'd go about
> >proving this though...
>
> Please rule out filesystem caches by issuing
>         sync;
>         echo 3 >/proc/sys/vm/drop_caches;

(Sorry if this goes to the list twice... Mailer problems.)

Ok, I did this on a non-production machine that has only been up for a
few hours, and here's what happened:

======== Before =========

$ free -m
            total       used       free     shared    buffers     cached
Mem:           878        824         54          0        111        422
-/+ buffers/cache:        290        587
Swap:           63          0         63

======== After ========

root@b0$ free -m
            total       used       free     shared    buffers     cached
Mem:           878         47        830          0          6          4
-/+ buffers/cache:         36        841
Swap:           63          0         63

======================

So, I guess it worked? (I don't know what was supposed to happen, but
memory usage dropped significantly when I did this.)

However, I'm not sure this staging machine has been up long enough or
doing enough to exhibit the problem. I can try this on my production
servers (the ones I provided graphs for) late tonight, but how safe is
running this command? Does it permanently disable file caching? Do I
need to reset it afterwards? If I stop all services (databases,
logging, etc) first, am I protected against data loss?
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