Messages in this thread | | | Date | Fri, 15 Jul 2011 14:31:37 +0100 | From | Ric Wheeler <> | Subject | Re: Mis-Design of Btrfs? |
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On 07/15/2011 02:20 PM, Chris Mason wrote: > 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
Absolutely sounds like the most sane way to go to me, thanks!
Ric
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