On 2011å03æ20æ 05:28, Theodore Ts'o Wrote:
This is an initial patchset of the bigalloc patches to ext4. This patch
adds support for clustered allocation, so that each bit in the ext4
block allocation bitmap addresses a power of two number of blocks. For
example, if the file system is mainly going to be storing large files in
the 4-32 megabyte range, it might make sense to set a cluster size of 1
megabyte. This means that each bit in the block allocaiton bitmap would
now address 256 4k blocks, and it means that the size of the block
bitmaps for a 2T file system shrinks from 64 megabytes to 256k. It also
means that a block group addresses 32 gigabytes instead of 128
megabytes, also shrinking the amount of file system overhead for
metadata.
The cost is increased disk space efficiency. Directories will consume
1T, as will extent tree blocks. (I am on the fence as to whether I
should add complexity so that in the rare case that an inode needs more
than 344 extents --- a highly fragmented file indeed --- and need a
second extent tree block, we can avoid allocating any cluster and
instead use another block from the cluster used by the inode. The
concern is the amount of complexity this adds to the e2fsck, not just to
the kernel.)
To test these patches, I have used an *extremely* kludgy set of patches
to e2fsprogs, which are attached below. These patches need *extensive*
revision before I would consider them clean enough suitable for
committing into e2fsprogs, but they were sufficient for me to do the
kernel-side changes --- mke2fs, dumpe2fs, and debugfs work. E2fsck most
definitely does _not_ work at this stage.
Please comment! I do not intend for these patches to be merged during
the 2.6.39 merge window. I am targetting 2.6.40, 3 months from now,
since these patches are quite extensive.
Hi Ted,
Is it possible to open a git repo/branch for both kernel and user space tools ? So others can follow, help or provide
performance number in time :-)
Thanks.
Coly
--
Coly Li
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