[PATCH v2 10/12] ubi: fastmap: Fix lapsed wear leveling for first 64 PEBs
Zhihao Cheng
chengzhihao1 at huawei.com
Sun Aug 27 23:38:43 PDT 2023
The anchor PEB must be picked from first 64 PEBs, these PEBs could have
large erase counter greater than other PEBs especially when free space
is nearly running out.
The ubi_update_fastmap will be called as long as pool/wl_pool is empty,
old anchor PEB is erased when updating fastmap. Given an UBI device with
N PEBs, free PEBs is nearly running out and pool will be filled with 1
PEB every time ubi_update_fastmap invoked. So t=N/POOL_SIZE[1]/64 means
that in worst case the erase counter of first 64 PEBs is t times greater
than other PEBs in theory.
After running fsstress for 24h, the erase counter statistics for two UBI
devices shown as follow(CONFIG_MTD_UBI_WL_THRESHOLD=128):
Device A(1024 PEBs, pool=50, wl_pool=25):
=========================================================
from to count min avg max
---------------------------------------------------------
0 .. 9: 0 0 0 0
10 .. 99: 0 0 0 0
100 .. 999: 0 0 0 0
1000 .. 9999: 0 0 0 0
10000 .. 99999: 960 29224 29282 29362
100000 .. inf: 64 117897 117934 117940
---------------------------------------------------------
Total : 1024 29224 34822 117940
Device B(8192 PEBs, pool=256, wl_pool=128):
=========================================================
from to count min avg max
---------------------------------------------------------
0 .. 9: 0 0 0 0
10 .. 99: 0 0 0 0
100 .. 999: 0 0 0 0
1000 .. 9999: 8128 2253 2321 2387
10000 .. 99999: 64 35387 35387 35388
100000 .. inf: 0 0 0 0
---------------------------------------------------------
Total : 8192 2253 2579 35388
The key point is reducing fastmap updating frequency by enlarging
POOL_SIZE, so let UBI reserve ubi->fm_pool.max_size PEBs during
attaching. Then POOL_SIZE will become ubi->fm_pool.max_size/2 even
in free space running out case.
Given an UBI device with 8192 PEBs(16384\8192\4096 is common
large-capacity flash), t=8192/128/64=1. The fastmap updating will
happen in either wl_pool or pool is empty, so setting fm_pool_rsv_cnt
as ubi->fm_pool.max_size can fill wl_pool in full state.
After pool reservation, running fsstress for 24h:
Device A(1024 PEBs, pool=50, wl_pool=25):
=========================================================
from to count min avg max
---------------------------------------------------------
0 .. 9: 0 0 0 0
10 .. 99: 0 0 0 0
100 .. 999: 0 0 0 0
1000 .. 9999: 0 0 0 0
10000 .. 99999: 1024 33801 33997 34056
100000 .. inf: 0 0 0 0
---------------------------------------------------------
Total : 1024 33801 33997 34056
Device B(8192 PEBs, pool=256, wl_pool=128):
=========================================================
from to count min avg max
---------------------------------------------------------
0 .. 9: 0 0 0 0
10 .. 99: 0 0 0 0
100 .. 999: 0 0 0 0
1000 .. 9999: 8192 2205 2397 2460
10000 .. 99999: 0 0 0 0
100000 .. inf: 0 0 0 0
---------------------------------------------------------
Total : 8192 2205 2397 2460
The difference of erase counter between first 64 PEBs and others is
under WL_FREE_MAX_DIFF(2*UBI_WL_THRESHOLD=2*128=256).
Device A: 34056 - 33801 = 255
Device B: 2460 - 2205 = 255
Next patch will add a switch to control whether UBI needs to reserve
PEBs for filling pool.
Fixes: dbb7d2a88d2a ("UBI: Add fastmap core")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=217787
Signed-off-by: Zhihao Cheng <chengzhihao1 at huawei.com>
---
drivers/mtd/ubi/build.c | 1 +
drivers/mtd/ubi/fastmap-wl.c | 2 +-
drivers/mtd/ubi/ubi.h | 2 ++
drivers/mtd/ubi/wl.h | 6 ++++--
4 files changed, 8 insertions(+), 3 deletions(-)
diff --git a/drivers/mtd/ubi/build.c b/drivers/mtd/ubi/build.c
index 8ee51e49fced..66d7b6a16aad 100644
--- a/drivers/mtd/ubi/build.c
+++ b/drivers/mtd/ubi/build.c
@@ -951,6 +951,7 @@ int ubi_attach_mtd_dev(struct mtd_info *mtd, int ubi_num,
UBI_FM_MIN_POOL_SIZE);
ubi->fm_wl_pool.max_size = ubi->fm_pool.max_size / 2;
+ ubi->fm_pool_rsv_cnt = ubi->fm_pool.max_size;
ubi->fm_disabled = (!fm_autoconvert || disable_fm) ? 1 : 0;
if (fm_debug)
ubi_enable_dbg_chk_fastmap(ubi);
diff --git a/drivers/mtd/ubi/fastmap-wl.c b/drivers/mtd/ubi/fastmap-wl.c
index 03c1f1016c0a..2a9cc9413c42 100644
--- a/drivers/mtd/ubi/fastmap-wl.c
+++ b/drivers/mtd/ubi/fastmap-wl.c
@@ -118,7 +118,7 @@ static void wait_free_pebs_for_pool(struct ubi_device *ubi)
* 4. beb_rsvd_pebs: This value should be get under lock ubi->wl_lock
*/
int reserved = WL_RESERVED_PEBS + EBA_RESERVED_PEBS +
- ubi->fm_size / ubi->leb_size - 1;
+ ubi->fm_size / ubi->leb_size - 1 + ubi->fm_pool_rsv_cnt;
do {
spin_lock(&ubi->wl_lock);
diff --git a/drivers/mtd/ubi/ubi.h b/drivers/mtd/ubi/ubi.h
index 423f66c91b1d..6e20a0fee72f 100644
--- a/drivers/mtd/ubi/ubi.h
+++ b/drivers/mtd/ubi/ubi.h
@@ -494,6 +494,7 @@ struct ubi_debug_info {
* @fast_attach: non-zero if UBI was attached by fastmap
* @fm_anchor: The next anchor PEB to use for fastmap
* @fm_do_produce_anchor: If true produce an anchor PEB in wl
+ * @fm_pool_rsv_cnt: Number of reserved PEBs for filling pool/wl_pool
*
* @used: RB-tree of used physical eraseblocks
* @erroneous: RB-tree of erroneous used physical eraseblocks
@@ -604,6 +605,7 @@ struct ubi_device {
int fast_attach;
struct ubi_wl_entry *fm_anchor;
int fm_do_produce_anchor;
+ int fm_pool_rsv_cnt;
/* Wear-leveling sub-system's stuff */
struct rb_root used;
diff --git a/drivers/mtd/ubi/wl.h b/drivers/mtd/ubi/wl.h
index 5ebe374a08ae..7b6715ef6d4a 100644
--- a/drivers/mtd/ubi/wl.h
+++ b/drivers/mtd/ubi/wl.h
@@ -10,8 +10,10 @@ static bool need_wear_leveling(struct ubi_device *ubi);
static void ubi_fastmap_close(struct ubi_device *ubi);
static inline void ubi_fastmap_init(struct ubi_device *ubi, int *count)
{
- /* Reserve enough LEBs to store two fastmaps. */
- *count += (ubi->fm_size / ubi->leb_size) * 2;
+ if (ubi->fm_disabled)
+ ubi->fm_pool_rsv_cnt = 0;
+ /* Reserve enough LEBs to store two fastmaps and to fill pools. */
+ *count += (ubi->fm_size / ubi->leb_size) * 2 + ubi->fm_pool_rsv_cnt;
INIT_WORK(&ubi->fm_work, update_fastmap_work_fn);
}
static struct ubi_wl_entry *may_reserve_for_fm(struct ubi_device *ubi,
--
2.39.2
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