Messages in this thread | | | Subject | Re: [PATCH] lightnvm: pblk: Introduce hot-cold data separation | From | Igor Konopko <> | Date | Fri, 26 Apr 2019 15:46:38 +0200 |
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On 26.04.2019 12:04, Javier González wrote: > >> On 26 Apr 2019, at 11.11, Igor Konopko <igor.j.konopko@intel.com> wrote: >> >> On 25.04.2019 07:21, Heiner Litz wrote: >>> Introduce the capability to manage multiple open lines. Maintain one line >>> for user writes (hot) and a second line for gc writes (cold). As user and >>> gc writes still utilize a shared ring buffer, in rare cases a multi-sector >>> write will contain both gc and user data. This is acceptable, as on a >>> tested SSD with minimum write size of 64KB, less than 1% of all writes >>> contain both hot and cold sectors. >> >> Hi Heiner >> >> Generally I really like this changes, I was thinking about sth similar since a while, so it is very good to see that patch. >> >> I have a one question related to this patch, since it is not very clear for me - how you ensure the data integrity in following scenarios: >> -we have open line X for user data and line Y for GC >> -GC writes LBA=N to line Y >> -user writes LBA=N to line X >> -we have power failure when both line X and Y were not written completely >> -during pblk creation we are executing OOB metadata recovery >> And here is the question, how we distinguish whether LBA=N from line Y or LBA=N from line X is the valid one? >> Line X and Y might have seq_id either descending or ascending - this would create two possible scenarios too. >> >> Thanks >> Igor >> > > You are right, I think this is possible in the current implementation. > > We need an extra constrain so that we only GC lines above the GC line > ID. This way, when we order lines on recovery, we can guarantee > consistency. This means potentially that we would need several open > lines for GC to avoid padding in case this constrain forces to choose a > line with an ID higher than the GC line ID. > > What do you think?
I'm not sure yet about your approach, I need to think and analyze this a little more.
I also believe that probably we need to ensure that current user data line seq_id is always above the current GC line seq_id or sth like that. We cannot also then GC any data from the lines which are still open, but I believe that this is a case even right now.
> > Thanks, > Javier >
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