Messages in this thread | | | Subject | Re: [PATCH] lightnvm: pblk: recover chunk state on 1.2 devices | From | Matias Bjørling <> | Date | Fri, 3 Aug 2018 14:46:40 +0200 |
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On 08/03/2018 02:37 PM, Javier Gonzalez wrote: >> On 3 Aug 2018, at 14.30, Matias Bjørling <mb@lightnvm.io> wrote: >> >> On 08/03/2018 02:02 PM, Javier Gonzalez wrote: >>>> On 3 Aug 2018, at 13.57, Matias Bjørling <mb@lightnvm.io> wrote: >>>> >>>> On 07/24/2018 09:54 AM, Javier Gonzalez wrote: >>>>>> On 29 Jun 2018, at 13.28, Matias Bjørling <mb@lightnvm.io> wrote: >>>>>> >>>>>> On 06/29/2018 01:22 PM, Javier Gonzalez wrote: >>>>>>>> On 29 Jun 2018, at 13.14, Matias Bjørling <mb@lightnvm.io> wrote: >>>>>>>> >>>>>>>> On 06/28/2018 11:12 AM, Javier González wrote: >>>>>>>>> The Open-Channel 1.2 spec does not define a mechanism for the host to >>>>>>>>> recover the block (chunk) state. As a consequence, a newly format device >>>>>>>>> will need to reconstruct the state. Currently, pblk assumes that blocks >>>>>>>>> are not erased, which might cause double-erases in case that the device >>>>>>>>> does not protect itself against them (which is not specified in the spec >>>>>>>>> either). >>>>>>>> >>>>>>>> It should not be specified in the spec. It is up to the device to handle >>>>>>>> double erases and not do it. >>>>>>>> >>>>>>>>> This patch, reconstructs the state based on read errors. If the first >>>>>>>>> sector of a block returns and empty page (NVM_RSP_ERR_EMPTYPAGE), then >>>>>>>>> the block s marked free, i.e., erased and ready to be used >>>>>>>>> (NVM_CHK_ST_FREE). Otherwise, the block is marked as closed >>>>>>>>> (NVM_CHK_ST_CLOSED). Note that even if a block is open and not fully >>>>>>>>> written, it has to be erased in order to be used again. >>>>>>>> >>>>>>>> Should we extend it to do the scan, and update the write pointer as >>>>>>>> well? I think this kind of feature already is baked into pblk? >>>>>>> This is already in place: we scan until empty page and take it from >>>>>>> there. This patch is only for the case in which we start a pblk instance >>>>>>> form scratch. On a device already owned by pblk, we would not have the >>>>>>> problem we are trying to solve here because we know the state. >>>>>> >>>>>> Agree. What I meant was that when we anyway are recovering the state, >>>>>> we could just as well update ->wp and set to NVM_CHK_ST_OPEN and so >>>>>> forth for the initialization phase. >>>>> In 1.2 the use of chunk metadata is purely fictional. We respect the >>>>> chunk state machine as we transition lines, but all the write pointers >>>>> are ignored. Instead, we use the line bitmap to point to the next >>>>> writable entry. This is BTW the same way we it in open lines on 2.0 too. >>>> >>>> Now I understand where you are coming from. I had the understanding >>>> that we where using the write pointer now that we moved to 2.0, >>>> looking through the code, that wasn't the case. :) Which means that >>>> pblk doesn't work with a devices that implements 2.0. Yikes... I knew >>>> I had forgot a detail when support was added into pblk. >>> I think you misunderstood; pblk does support 2.0 devices. What happens >>> is that we transform the per chunk WP in 2.0 into the line bitmap to >>> simplify the lookup. The point being that we do not need to create a >>> fictional chunk for 1.2 devices since we do the translation to the >>> bitmap directly. Does this make sense? >> >> The chunk->wp isn't used anywhere. So it can't take wp into account. >> It uses the EMPTYPAGE marker from 1.2 instead. See pblk-core and >> pblk-recovery. >> > > I see that the patches for this are still internal. Will post for 4.20 >
Thanks. Please also put a Fixes: on, so it gets backported appropriately.
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