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Improving ext4: bigalloc, inline data, and metadata checksumsImproving ext4: bigalloc, inline data, and metadata checksumsPosted Dec 12, 2011 18:15 UTC (Mon) by andresfreund (subscriber, #69562)In reply to: Improving ext4: bigalloc, inline data, and metadata checksums by dlang Parent article: Improving ext4: bigalloc, inline data, and metadata checksums
The do wait for journaled data uppon journal commit. Which is the place where barriers are issued anyway.
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Improving ext4: bigalloc, inline data, and metadata checksums Posted Dec 12, 2011 18:39 UTC (Mon) by dlang (✭ supporter ✭, #313) [Link]
issueing barriers is _how_ the filesystem 'waits'
it actually doesn't stop processing requests and wait for the confirmation from the disk, it issues a barrier to tell the rest of the storage stack not to reorder around that point and goes on to process the next requrest and get it in flight.
Improving ext4: bigalloc, inline data, and metadata checksums Posted Dec 12, 2011 18:53 UTC (Mon) by andresfreund (subscriber, #69562) [Link]
Err. Read the code. xfs uses io completion callbacks and only relies on the contents of the journal after the completion returned. (xlog_sync()->xlog_bdstrat()->xfs_buf_iorequest()->_xfs_buf_ioend()).
jbd does something similar but I don't want to look it up unless youre really interested.
It worked a littlebit more like you describe before 2.6.37 but back then it waited if barriers were disabled.
Improving ext4: bigalloc, inline data, and metadata checksums Posted Dec 13, 2011 13:35 UTC (Tue) by nix (subscriber, #2304) [Link]
Well, this is clear as mud :) guess I'd better do some code reading and figure out wtf the properties of the system actually are...
Improving ext4: bigalloc, inline data, and metadata checksums Posted Dec 13, 2011 13:38 UTC (Tue) by andresfreund (subscriber, #69562) [Link]
If you want I can give you the approx calltrace for jbd2 as well, I know it took me some time when I looked it up...
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