[PATCH 00/37] e2fsprogs patchbomb 5/14

Darrick J. Wong
2014-05-01T23:12:29Z

Welp, time for another patchbomb! As usual, the patchbomb starts with
8 minor bug fixes. The first two add some extra reporting and fix
Coverity bugs. Patch 3 adds the ability to create sockets when
performing mke2fs -D. Patch 4 changes mke2fs to always complain when
formatting inline_data with 128-byte inodes. Patch 5-6 fix some
problems when dumping journals in debugfs. Patch 7 fixes a bug in
resize2fs when sparse_super2. Patch 8 fixes a bug in mke2fs where
block group checksums weren't being set when the user specifies packed
metadata blocks. Patch 9 adds an extended option to mke2fs so that
users can set the error behavior at format time.

Patches 10-14 make some alterations to metadata checksumming support;
by default, e2fsck will now check the inode before verifying the
checksum. There's a command line option to restore the "just scrape
it off the system" behavior for heavily damaged filesystems. There
are a couple of patches to fix erroneous behavior and crashes when
e2fsck has to rebuild the root directory. The final patch in this
clump adds a command line option to dumpe2fs to ignore checksum
failures.

Patch 15 enables block_validity for new filesystems. As noted here
previously, the overhead of enabling this option seems to be at most a
1% performance hit when performing a lot of small allocations, and
negligible otherwise. On the plus side, the filesystem is smarter
about noticing erroneous allocations out of metadata areas (i.e. block
bitmap corruption) and shutting itself down to prevent damage.

Patches 16-17 enhance ext2fs_bmap2() to allow the creation of
uninitialized extents. The functionality is already there; really it
just adds a flag to indicate uninitialized. There's also a patch to
the fileio routines to handle uninitialized extents. These patches
are unchanged from December.

Patches 18-20 add to resize2fs the ability to convert a filesystem to
and from 64bit mode. These patches are unchanged from December.

Patches 21-24 implement readahead for e2fsck. The first patch tries
to reduce system call overhead by using pread/pwrite if available.
The next two patches plumb in the IO manager and library changes
necessary to read metadata blocks into the page cache (on Linux). The
final patch teaches e2fsck to use the library readahead functions in a
separate thread.

Crude testing has been done via:
# echo 3 > /proc/sys/vm/drop_caches
# e2fsck -Fnfvtt /dev/XXX

So far in my crude testing on a cold system, I've seen about a ~20%
speedup on a SSD, a ~40% speedup on a 3x RAID1 SATA array, and about
a 10% speedup on a single-spindle SATA disk. On a single-queue USB
HDD, performance doesn't change much. It looks as though low end
storage like USB HDDs will not benefit, which doesn't surprise me.
There's around a 2% regression for USB HDDs, though it doesn't seem
statistically significant. The SSD numbers are harder to quantify
since they're already fast. Somewhat unexpectedly, the readahead code
speeds up e2fsck even when the page cache has already been warmed up.

This third version of the readahead patches try to prevent page cache
thrashing by limiting the amount of (user-configurable) readahead to a
default of half of physical memory. It also tries to release some of
the memory pages if it can conclude that it's totally done with a
block, and it can now detect very slow readahead and disable it.

Patches 25-29 implement fallocate for e2fsprogs, and modifies Ted's
mk_hugefiles functionality to use it. The general fallocate API call
is (regrettably) much more complex than Ted's, since it must grapple
with the possibility that the file already has mapped blocks. There
were also a lot of bigalloc related subtleties.

Patches 30-33 implement fuse2fs, a FUSE server based on libext2fs.
Primarily I've been using it to shake out bugs in the library via
xfstests and the metadata checksumming test program. It can also be
used to mount ext4 on any OS supporting FUSE, and it can also mount
64k-block filesystems on x86, though I'd be wary of using rw mode.
fuse2fs depends on these new APIs: xattr editing, uninit extent
handling, and the new fallocate call.

Patches 34-36 provide the metadata checksumming test script. Its
primary advantage over 'make check' is that it allows one to specify a
variety of different mkfs and mount options. It's also growing more
tests as a result of fuse2fs exercise.

Patch 37 introduces ext5, which reduces our testing matrix by
requiring a fairly large set of features and eliminating most mount
options. True, not all the features are stable or ready for
production yet, but six years after ext4 we have a bunch of new
features ready for wider testing.

I've tested these e2fsprogs changes against the -next branch as of
4/17. These days, I use several VMs, each with 8GB ramdisks to test
with; the test process is checkpatch > make C=1 > make check >
metadata checksum tests > fuse + xfstests.

Comments and questions are, as always, welcome.

--D