Messages in this thread | | | Subject | Re: [PATCH v3] lightnvm: physical block device (pblk) target | From | Matias Bjørling <> | Date | Mon, 10 Apr 2017 19:47:08 +0200 |
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On 04/10/2017 05:55 PM, Bart Van Assche wrote: > On Sun, 2017-04-09 at 11:15 +0200, Javier González wrote: >> On 8 Apr 2017, at 22.56, Bart Van Assche <bart.vanassche@sandisk.com> wrote: >>> On 04/07/17 11:50, Javier González wrote: >> struct ppa_addr, which is the physical address format is not affected, >> but pblk's internal L2P address representation (pblk_addr) is. You can >> see that the type either represents struct ppa_addr or ppa_addr_32. How >> would you define a type that can either be u64 or u32 with different bit >> offsets at run-time? Note that address conversions to this type is in >> the fast path and this format allows us to only use bit shifts. > > Selecting the appropriate representation at run-time would require to pass > pblk_addr by reference instead of by value to any function that expects a > pblk_addr. It would also require to have two versions of every data structure > that depends on pblk_addr and to use casts to convert to the appropritate > version. However, this approach is probably only worth to be implemented if > it doesn't introduce too much additional complexity. >
Hi Bart, thanks for the feedback!
I've spent the time today to implement it such that 32bit entries are used if the device addressing can fit. We do see a slight overhead, however not enough to be a deal-breaker. We'll post an updated version with the flag removed.
>>>> +#ifdef CONFIG_NVM_DEBUG >>>> + atomic_add(nr_entries, &pblk->inflight_writes); >>>> + atomic_add(nr_entries, &pblk->req_writes); >>>> +#endif >>> >>> Has it been considered to use the "static key" feature such that >>> consistency checks can be enabled at run-time instead of having to >>> rebuild the kernel to enable CONFIG_NVM_DEBUG? >> >> I haven't considered it. I'll look into it. I would like to have this >> counters and the corresponding sysfs entry only available on debug mode >> since it allows us to have a good picture of the FTL state. > > If there are sysfs entries that depend on CONFIG_NVM_DEBUG then the static > key mechanism is probably not a good alternative for CONFIG_NVM_DEBUG. > >>> Has it been considered to add support for keeping a subset of the L2P >>> translation table in memory instead of keeping it in memory in its entirety? >> >> Yes. L2P caching is on our roadmap and will be included in the future. > > That's great. This will also help with reducing the time between discovery of > a lightnvm device and the time at which I/O can start since the L2P table must > be available before I/O can start.
Definitely. I would love if one could jump in and implement it. We have a bunch of features that we want in before implementing a translation cache. > > Bart. >
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