Messages in this thread | | | Date | Thu, 27 Nov 2014 17:13:43 +0100 | From | Richard Weinberger <> | Subject | Re: [PATCH 2/6] UBI: Fastmap: Ensure that only one fastmap work is scheduled |
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Am 27.11.2014 um 16:27 schrieb Artem Bityutskiy: > On Mon, 2014-11-24 at 14:20 +0100, Richard Weinberger wrote: >> If the WL pool runs out of PEBs we schedule a fastmap write >> to refill it as soon as possible. >> Ensure that only one at a time is scheduled otherwise we might end in >> a fastmap write storm because writing the fastmap can schedule another >> write if bitflips are detected. > > Could you please provide some more details about the "write storm". Does > it happen when there are 2 fastmap works in the queue? Or if they run > simultaneously? Why the storm happens and white kind of "writes" it > consists of?
If UBI needs to write a new fastmap while wear leveling (by using get_peb_for_wl()) a fastmap work is scheduled. We cannot write a fastmap in this context because we're in atomic context. At this point one fastmap write is scheduled. If now get_peb_for_wl() is executed a second time it will schedule another fastmap work because the pools are still not refilled. This will go on until finally a fastmap got written. Either by the the kworker or ubi_wl_get_peb(). As now a lot of fastmap works are scheduled they all will be issues in series. Hence, a write storm. :)
Thanks, //richard
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