Fwd: ubi: fastmap: Fix a series of wear leveling problems

[Bagas Sanjaya <bagasdotme@gmail.com>]

Hi,

I notice a bug report with proposed fixes on Bugzilla [1]. Quoting from it
(only the first problem that is quoted):

> Problem 1: large erase counter for single fastmap data PEB
> 
> Config:
> x86_64 qemu
> flash: nandsim
> CONFIG_MTD_UBI_WL_THRESHOLD=128
> CONFIG_MTD_UBI_FASTMAP=y
> ubi->beb_rsvd_pebs=0
> 
> Running fsstress on ubifs for 3h(fastmap data PEB has large erase counter than others):
> =========================================================
> from              to     count      min      avg      max
> ---------------------------------------------------------
> 0        ..        9:        0        0        0        0
> 10       ..       99:      532       84       92       99
> 100      ..      999:    15787      100      147      229
> 1000     ..     9999:       64     4699     4765     4826
> 10000    ..    99999:        0        0        0        0
> 100000   ..      inf:        1   272935   272935   272935
> ---------------------------------------------------------
> Total               :    16384       84      180   272935
> PEB 8031(ec=272935) is always taken for fastmap data.
> 
> After fix, running fsstress on ubifs for 12h(no pool reservation), no individual peb has big erase counter:
> =========================================================
> from              to     count      min      avg      max
> ---------------------------------------------------------
> 0        ..        9:        0        0        0        0
> 10       ..       99:        0        0        0        0
> 100      ..      999:    16320      609      642      705
> 1000     ..     9999:        0        0        0        0
> 10000    ..    99999:       64    18176    18234    18303
> 100000   ..      inf:        0        0        0        0
> ---------------------------------------------------------
> Total               :    16384      609      710    18303

See Bugzilla for the full thread (with other problems mentioned) and
attached patch series that fixes them.

Zhihao: I asked you on BZ to send your patches to linux-mtd list,
but you didn't respond there. Would you like to send them for
review?

Thanks.

[1]: https://bugzilla.kernel.org/show_bug.cgi?id=217787

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