Heads up: e2fsprogs-1.42-WIP-0702 pushed to rawhide
sandeen at redhat.com
Thu Oct 6 14:34:37 UTC 2011
On 10/5/11 12:54 PM, Richard W.M. Jones wrote:
> On Wed, Oct 05, 2011 at 09:58:59AM -0500, Eric Sandeen wrote:
>> right; for large ext4 fs use (or testing), try
>> # mkfs.ext4 -E lazy_itable_init=1 /dev/blah
>> this will cause it to skip inode table initialization, and speed up
>> mkfs a LOT. It'll also keep sparse test images smaller.
>> IMHO this should probably be made default above a certain size.
> You almost preempted my question: Could I use this for every ext4
> filesystem I make? Honestly from a virt / libguestfs p.o.v. it sounds
> like something we should always do.
Yes, and sorry for the earlier confusion - it should be on by default
for newer kernels + e2fsprogs.
>> The tradeoff is that inode table initialization happens in
>> kernelspace, post-mount - with efforts made to do it in the
>> background, and not impact other I/O too much.
> Is there a circumstance where this is bad? I'm thinking perhaps a
> case where you create a filesystem and immediately try to populate it
> with lots of files.
I do have some concerns about that. I think it will take some careful
benchmarking to know for sure whether it is an issue.
Commit bfff68738f1cb5c93dab1114634cea02aae9e7ba has a good summary
of how it all works, and what some impact on early fs operations may
> We do not disturb regular inode allocations in any way, it just do not
> care whether the inode table is, or is not zeroed. But when zeroing, we
> have to skip used inodes, obviously. Also we should prevent new inode
> allocations from the group, while zeroing is on the way. For that we
> take write alloc_sem lock in ext4_init_inode_table() and read alloc_sem
> in the ext4_claim_inode, so when we are unlucky and allocator hits the
> group which is currently being zeroed, it just has to wait.
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