Message-ID: <522752DE.7090308@hp.com>
Date: Wed, 04 Sep 2013 15:33:50 +0000
From: Thavatchai Makphaibulchoke <thavatchai.makpahibulchoke@hp.com>
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130803 Thunderbird/17.0.8
MIME-Version: 1.0
To: Andreas Dilger <adilger@dilger.ca>
CC: T Makphaibulchoke <tmac@hp.com>, "Theodore Ts'o" <tytso@mit.edu>,
        Al Viro <viro@zeniv.linux.org.uk>,
        "linux-ext4@vger.kernel.org List" <linux-ext4@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "linux-fsdevel@vger.kernel.org Devel" <linux-fsdevel@vger.kernel.org>,
        aswin@hp.com, Linus Torvalds <torvalds@linux-foundation.org>,
        aswin_proj@groups.hp.com
Subject: Re: [PATCH v3 0/2] ext4: increase mbcache scalability
References: <1374108934-50550-1-git-send-email-tmac@hp.com> <1378312756-68597-1-git-send-email-tmac@hp.com> <FDD6EB21-7C40-4F4D-904C-8514535CC7C3@dilger.ca>
In-Reply-To: <FDD6EB21-7C40-4F4D-904C-8514535CC7C3@dilger.ca>
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1587
Lines: 33

On 09/04/2013 08:00 PM, Andreas Dilger wrote:

> 
> In the past, I've raised the question of whether mbcache is even
> useful on real-world systems.  Essentially, this is providing a
> "deduplication" service for ext2/3/4 xattr blocks that are identical.
> The question is how often this is actually the case in modern use?
> The original design was for allowing external ACL blocks to be
> shared between inodes, at a time when ACLs where pretty much the
> only xattrs stored on inodes.
> 
> The question now is whether there are common uses where all of the
> xattrs stored on multiple inodes are identical?  If that is not the
> case, mbcache is just adding overhead and should just be disabled
> entirely instead of just adding less overhead.
> 
> There aren't good statistics on the hit rate for mbcache, but it
> might be possible to generate some with systemtap or similar to
> see how often ext4_xattr_cache_find() returns NULL vs. non-NULL.
> 
> Cheers, Andreas
> 

Thanks Andreas for the comments.  Since I'm not familiar with systemtap, I'm thinking probably the quickest and simplest way is to re-run aim7 and swing bench with mbcache disabled for comparison. Please let me know if you have any other benchmark suggestion or if you think systemtap on ext4_xattr_cache_find() would give a more accurate measurement.

Thanks,
Mak.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/