Messages in this thread | | | From | Chris Mason <> | Subject | Re: Mis-Design of Btrfs? | Date | Fri, 15 Jul 2011 09:20:00 -0400 |
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Excerpts from Ric Wheeler's message of 2011-07-15 08:58:04 -0400: > On 07/15/2011 12:34 PM, Chris Mason wrote:
[ triggering IO retries on failed crc or other checks ]
> > > > But, maybe the whole btrfs model is backwards for a generic layer. > > Instead of sending down ios and testing when they come back, we could > > just set a verification function (or stack of them?). > > > > For metadata, btrfs compares the crc and a few other fields of the > > metadata block, so we can easily add a compare function pointer and a > > void * to pass in. > > > > The problem is the crc can take a lot of CPU, so btrfs kicks it off to > > threading pools so saturate all the cpus on the box. But there's no > > reason we can't make that available lower down. > > > > If we pushed the verification down, the retries could bubble up the > > stack instead of the other way around. > > > > -chris > > I do like the idea of having the ability to do the verification and retries down > the stack where you actually have the most context to figure out what is possible... > > Why would you need to bubble back up anything other than an error when all > retries have failed?
By bubble up I mean that if you have multiple layers capable of doing retries, the lowest levels would retry first. Basically by the time we get an -EIO_ALREADY_RETRIED we know there's nothing that lower level can do to help.
-chris
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