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Subject: Re: [PATCH 0/4] linux-2.6-block: deactivating pagecache for
	benchmarks
From: Badari Pulavarty <pbadari@gmail.com>
To: Andrew Morton <akpm@osdl.org>
Cc: Dirk Henning Gerdes <mail@dirk-gerdes.de>, axboe@suse.de,
       lkml <linux-kernel@vger.kernel.org>
In-Reply-To: <20051201172520.7095e524.akpm@osdl.org>
References: <1133443051.6110.32.camel@noti>
	 <20051201172520.7095e524.akpm@osdl.org>
Content-Type: text/plain
Date: Mon, 05 Dec 2005 08:54:16 -0800
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On Thu, 2005-12-01 at 17:25 -0800, Andrew Morton wrote:
> Dirk Henning Gerdes <mail@dirk-gerdes.de> wrote:
> >
> >  For doing benchmarks on the I/O-Schedulers, I thought it would be very
> >  useful to disable the pagecache.
> 
> That's an FAQ.   Something like this?
> 
> 
> From: Andrew Morton <akpm@osdl.org>
> 
> Add /proc/sys/vm/drop-pagecache.  When written to, this will cause the kernel
> to discard as much pagecache and reclaimable slab objects as it can.
> 
> It won't drop dirty data, so the user should run `sync' first.

BTW, (a while ago) I tried doing similar thing from user-space 
using POSIX_FADV_DONTNEED on a file. While it worked great to 
get rid of the pagecache pages for few files, since I had to 
run this on each and every file in the filesystem - it ended 
up bloating inode, dentry slabs :( I really wanted to find out 
what files are really cached in the pagecache to run this on.

Thanks,
Badari

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