linux-ext4 - Re: [PATCH v3 0/2] ext4: increase mbcache scalability

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Date:	Wed, 11 Sep 2013 14:33:59 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	"Theodore Ts'o" <tytso@....edu>,
	Andreas Dilger <adilger@...ger.ca>,
	Thavatchai Makphaibulchoke <thavatchai.makpahibulchoke@...com>,
	T Makphaibulchoke <tmac@...com>,
	Al Viro <viro@...iv.linux.org.uk>,
	"linux-ext4@...r.kernel.org List" <linux-ext4@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org Devel" <linux-fsdevel@...r.kernel.org>,
	aswin@...com, Linus Torvalds <torvalds@...ux-foundation.org>,
	aswin_proj@...ts.hp.com
Subject: Re: [PATCH v3 0/2] ext4: increase mbcache scalability

On 9/11/13 11:49 AM, Eric Sandeen wrote:
> On 9/11/13 6:30 AM, Theodore Ts'o wrote:
>> On Tue, Sep 10, 2013 at 10:13:16PM -0500, Eric Sandeen wrote:
>>>
>>> Above doesn't tell us the prevalence of various contexts on the actual system,
>>> but they are all under 100 bytes in any case.
>>
>> OK, so in other words, on your system i_file_acl and i_file_acl_high
>> (which is where we store the block # for the external xattr block),
>> should always be zero for all inodes, yes?
> 
> Oh, hum - ok, so that would have been the better thing to check (or at
> least an additional thing).
> 
> # find / -xdev -exec filefrag -x {} \; | awk -F : '{print $NF}' | sort | uniq -c
> 
> Finds quite a lot that claim to have external blocks, but it seems broken:
> 
> # filefrag -xv /var/lib/yum/repos/x86_64/6Server/epel
> Filesystem type is: ef53
> File size of /var/lib/yum/repos/x86_64/6Server/epel is 4096 (1 block, blocksize 4096)
>  ext logical physical expected length flags
>    0       0 32212996252             100 not_aligned,inline
> /var/lib/yum/repos/x86_64/6Server/epel: 1 extent found
> 
> So _filefrag_ says it has a block (at a 120T physical address not on my fs!)

Oh, this is the special-but-not-documented "print inline extents in bytes
not blocks"  :(

I'll send a patch to ignore inline extents on fiemap calls to make this
easier, but in the meantime, neither my RHEL6 root nor my F17 root have
any out-of-inode selinux xattrs on 256-byte-inode filesystems.

So selinux alone should not be exercising mbcache much, if at all, w/ 256 byte
inodes.

-Eric
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