From: Theodore Ts'o <tytso@mit.edu>
To: Phillip Susi <psusi@ubuntu.com>
Cc: Zheng Liu <gnehzuil.liu@gmail.com>,
linux-ext4@vger.kernel.org, Zheng Liu <wenqing.lz@taobao.com>
Subject: Re: [PATCH 3/3] mke2fs: document bigalloc and cluster-size
Date: Tue, 15 Jan 2013 14:57:41 -0500 [thread overview]
Message-ID: <20130115195741.GG17719@thunk.org> (raw)
In-Reply-To: <50F5B209.40900@ubuntu.com>
On Tue, Jan 15, 2013 at 02:46:17PM -0500, Phillip Susi wrote:
>
> Does this mean that a cluster is the minimum allocation unit, or can
> two small files allocate different blocks in the same cluster, leaving
> the cluster partially used? If the former, then how is this different
> than just using a larger block size?
The former. The difference is that we use units of blocks in the
indirect blocks and extents --- and the reason for this is because
there's a pretty fundamental limitation baked into the MM layer that
the file system block size is less than or equal to the page size. So
on architectures where we have 16k page sizes, we can use a 16k block
size --- but then you won't be able to mount that file system on an
x86 system.
So bigalloc is basically a hack because it was easier to make this
change in the file system than it is to deal with block sizes greater
than the page size.
- Ted
next prev parent reply other threads:[~2013-01-15 19:57 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-01-13 9:08 [PATCH 1/3] mke2fs: indicate bigalloc feature explicity when cluster-size is enabled Zheng Liu
2013-01-13 9:08 ` [PATCH 2/3] mke2fs: reduce the range of cluster-size Zheng Liu
2013-01-14 17:41 ` Andreas Dilger
2013-01-14 21:03 ` Theodore Ts'o
2013-01-14 21:07 ` Andreas Dilger
2013-01-14 21:10 ` Theodore Ts'o
2013-01-15 0:37 ` [PATCH 1/5] mke2fs: enforce that the cluster size must be less that the block size Theodore Ts'o
2013-01-15 0:37 ` [PATCH 2/5] mke2fs: the -g option will now specify the clusters per block group Theodore Ts'o
2013-01-15 15:10 ` Eric Sandeen
2013-01-15 19:05 ` Theodore Ts'o
2013-01-15 15:22 ` Zheng Liu
2013-01-15 0:37 ` [PATCH 3/5] libe2p: teach parse_num_blocks2() to return bytes if log_block_size < 0 Theodore Ts'o
2013-01-15 15:23 ` Zheng Liu
2013-01-15 0:37 ` [PATCH 4/5] mke2fs: teach mke2fs to understand -b 4k and -C 256M Theodore Ts'o
2013-01-15 15:11 ` Eric Sandeen
2013-01-15 15:13 ` Eric Sandeen
2013-01-15 15:24 ` Zheng Liu
2013-01-15 0:37 ` [PATCH 5/5] libext2fs: avoid 32-bit overflow in ext2fs_initialize with a 512M cluster size Theodore Ts'o
2013-01-15 15:33 ` Zheng Liu
2013-01-15 15:36 ` Zheng Liu
2013-01-15 19:10 ` Theodore Ts'o
2013-01-16 1:49 ` Zheng Liu
2013-01-15 0:41 ` [PATCH 1/5] mke2fs: enforce that the cluster size must be less that the block size Theodore Ts'o
2013-01-15 15:22 ` Zheng Liu
2013-01-13 9:08 ` [PATCH 3/3] mke2fs: document bigalloc and cluster-size Zheng Liu
2013-01-15 3:10 ` Theodore Ts'o
2013-01-15 19:12 ` Theodore Ts'o
2013-01-15 19:46 ` Phillip Susi
2013-01-15 19:57 ` Theodore Ts'o [this message]
2013-01-15 20:38 ` Phillip Susi
2013-01-15 22:28 ` Theodore Ts'o
2013-01-14 20:28 ` [PATCH 1/3] mke2fs: indicate bigalloc feature explicity when cluster-size is enabled Theodore Ts'o
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