linux-kernel - Re: Drop cache has no effect?

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Message-Id: <20060829124945.656dbaa1.akpm@osdl.org>
Date:	Tue, 29 Aug 2006 12:49:45 -0700
From:	Andrew Morton <akpm@...l.org>
To:	Jan Engelhardt <jengelh@...ux01.gwdg.de>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Subject: Re: Drop cache has no effect?

On Tue, 29 Aug 2006 21:21:25 +0200 (MEST)
Jan Engelhardt <jengelh@...ux01.gwdg.de> wrote:

> >> -rw-r--r--   1 jengelh users 37816633 2006-07-28 19:25 
> >> inkscape-0.44-2.guru.suse101.i686.rpm
> >> -rw-r--r--   1 jengelh users   297243 2006-08-15 01:13 
> >> vmware-any-any-update104.tar.gz
> >> 
> >> Remains 644.
> >
> >That would be a vfat problem - the changed permission bits weren't written
> >back to disk, so when you re-read them from disk (or, more likely, from
> >blockdev pagecache) they came back with the original values.
> 
> Yes, that's _intended_.
> 
> Fact:
> If you chmod 644 some files on vfat, then unmount and mount it again, they show
> up as 755 again. That is ok.
> 
> Observation:
> Dropping the cache does not imply the 644->755 change observed on unmount.
> 
> Conclusion:
> Caches not dropped.

Not all caches dropped.  It'd be silly to try that - see the implementation.

Running the same command a few more times might wring a couple more dentries
and inodes out of it.
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