From: Ted Ts'o <tytso@mit.edu>
To: Andreas Dilger <adilger.kernel@dilger.ca>
Cc: Ext4 Developers List <linux-ext4@vger.kernel.org>
Subject: Re: [PATCH 6/6] ext4: Dynamically allocate the jbd2_inode in ext4_inode_info as necessary
Date: Tue, 11 Jan 2011 16:50:43 -0500 [thread overview]
Message-ID: <20110111215043.GG2917@thunk.org> (raw)
In-Reply-To: <A562E0CA-9CA6-4654-8FCB-9849F6EB09E7@dilger.ca>
On Wed, Jan 05, 2011 at 12:26:33PM -0700, Andreas Dilger wrote:
>
> How does this change impact the majority of users that are running
> with a journal? It is clearly a win for a small percentage of users
> with no-journal mode, but it may be a net increase in memory usage
> for the majority of the users (with journal)....
>
> The main question is how many files are ever opened for write? It
> isn't just the number of currently-open files for write, because the
> jinfo isn't released until the inode is cleared from memory. While
> I suspect that most inodes in cache are never opened for write, it
> would be worthwhile to compare the ext4_inode_cache object count
> against the jbd2_inode object count, and see how the total memory
> compares to a before-patch system running different workloads (with
> journal).
So here's one unscientific data point, based on your humble kernel
developer who happens to read e-mail using mutt and a Maildir
directory (which has lots of read-only files, one per e-mail) and does
primarily source code editing, kernel builds, web browsing, e-mail,
and irc/IM:
Slabcache: ext4_inode_cache Aliases: 0 Order : 3 Objects: 70820
Slabcache: jbd2_inode Aliases: 5 Order : 0 Objects: 22126
Note that jbd2_inode is aliased, so not all 22,126 objects are
necessarily jbd2_inodes. Some of them might also be ip_fib_alias,
ksm_mm_slot, anon_vma_chain, Acpi-Parse, and nsproxy objects. But
still, the ratio of inodes that I've ever written to inodes that have
only been accessed read-only is over 3:1.
So for at least my laptop/desktop workload, using a separate
jbd2_inode structure is clearly a win, and in fact separating out more
of the ext4_inode_cache structure to create a separate data structure
for fieldsonly needed when the file is opened for writing would likely
be a win. I can probably peel off another 100 bytes or so from the
ext4_inode_info data structure.
- Ted
prev parent reply other threads:[~2011-01-11 21:50 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-01-05 1:01 [PATCH 0/6] Shrinking the size of ext4_inode_info Theodore Ts'o
2011-01-05 1:01 ` [PATCH 1/6] ext4: replace i_delalloc_reserved_flag with EXT4_STATE_DELALLOC_RESERVED Theodore Ts'o
2011-01-05 1:01 ` [PATCH 2/6] ext4: Use ext4_lblk_t instead of sector_t for logical blocks Theodore Ts'o
2011-01-05 1:01 ` [PATCH 3/6] ext4: Drop ec_type from the ext4_ext_cache structure Theodore Ts'o
2011-01-05 1:01 ` [PATCH 4/6] ext4: reorder ext4_inode_info structure elements to remove unneeded padding Theodore Ts'o
2011-01-05 1:01 ` [PATCH 5/6] ext4: Drop i_state_flags on architectures with 64-bit longs Theodore Ts'o
2011-01-05 18:43 ` Andreas Dilger
2011-01-05 20:29 ` Ted Ts'o
2011-01-06 7:23 ` Andreas Dilger
2011-01-06 17:55 ` Ted Ts'o
2011-01-06 21:15 ` [PATCH] " Theodore Ts'o
2011-01-05 1:01 ` [PATCH 6/6] ext4: Dynamically allocate the jbd2_inode in ext4_inode_info as necessary Theodore Ts'o
2011-01-05 9:26 ` Amir Goldstein
2011-01-05 20:21 ` Ted Ts'o
2011-01-05 19:26 ` Andreas Dilger
2011-01-05 20:21 ` Ted Ts'o
2011-01-06 22:14 ` Ted Ts'o
2011-01-07 2:36 ` [PATCH -v2] " Theodore Ts'o
2011-01-07 20:46 ` Amir Goldstein
2011-01-07 22:40 ` Ted Ts'o
2011-01-11 21:50 ` Ted Ts'o [this message]
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