Messages in this thread | | | Subject | Re: [PATCH] lightnvm: pblk: recover chunk state on 1.2 devices | From | Matias Bjørling <> | Date | Fri, 3 Aug 2018 14:30:56 +0200 |
| |
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.
> >> There are no empty sector marker in the 2.0 spec, since it uses the >> write pointer to know where it is in the chunk. So there is a bit of >> work to do there. >> > > Yes. And for 2.0 devices we go and look at the WP, but for 1.2 devices we > need to scan. > >> Since this properly is a bit more work to do, I'll look into it after FMS. >> > > Look the comments above. All we need for 2.0 support is in place. We can > talk about it f2f. > >> I'm also moving the explicit coding of 1.2/2.0 chunk / bad block >> fixing into core, so pblk can be simplfied, and doesn't have to think >> to manage each version separately. >> > > Good. I have a patch I was expecting to send after FMS for moving chunk > / bad block out of pblk for the same reason. If you're doing the same > thing I can stop looking into it...
I am, will post when done.
> >> >>> Chunk metadata is only used to setup the bitmaps on init/recovery. From >>> here on, we use the bitmap to find the next writable sector, without >>> worrying about the specific per-chunk write pointer. Thus, updating >>> chunk metadata here has no effect. >>> Does this make sense to you? >>> Javier
| |