ubi: fastmap: may_reserve_for_fm: Don't reserve PEB if fm_anchor exists
This is the part 1 to fix cyclically reusing single fastmap data PEBs.
After running fsstress on UBIFS for a while, UBI (16384 blocks, fastmap
takes 2 blocks) has an erase block(PEB: 8031) with big erase counter
greater than any other pebs:
=========================================================
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
Not like fm_anchor, there is no candidate PEBs for fastmap data area,
so old fastmap data pebs will be reused after all free pebs are filled
into pool/wl_pool:
ubi_update_fastmap
for (i = 1; i < new_fm->used_blocks; i++)
erase_block(ubi, old_fm->e[i]->pnum)
new_fm->e[i] = old_fm->e[i]
According to wear leveling algorithm, UBI selects one small erase
counter PEB from ubi->used and one big erase counter PEB from wl_pool,
the reused fastmap data PEB is not in these trees. UBI won't schedule
this PEB for wl even it is in ubi->used because wl algorithm expects
small erase counter for used PEB.
Don't reserve PEB for fastmap in may_reserve_for_fm() if fm_anchor
already exists. Otherwise, when UBI is running out of free PEBs,
the only one free PEB (pnum < 64) will be skipped and fastmap data
will be written on the same old PEB.
Fixes: dbb7d2a88d2a ("UBI: Add fastmap core")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=217787
Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
2 files changed
