[PATCH v2 1/2] ubi: fastmap: Fix high cpu usage of ubi_bgt by making sure wl_pool not empty
Zhihao Cheng
chengzhihao1 at huawei.com
Fri May 6 00:17:03 PDT 2022
There at least 6 PEBs reserved on UBI device:
1. EBA_RESERVED_PEBS[1]
2. WL_RESERVED_PEBS[1]
3. UBI_LAYOUT_VOLUME_EBS[2]
4. MIN_FASTMAP_RESERVED_PEBS[2]
When all ubi volumes take all their PEBs, there are 3 (EBA_RESERVED_PEBS +
WL_RESERVED_PEBS + MIN_FASTMAP_RESERVED_PEBS - MIN_FASTMAP_TAKEN_PEBS[1])
free PEBs. Since f9c34bb529975fe ("ubi: Fix producing anchor PEBs") and
4b68bf9a69d22dd ("ubi: Select fastmap anchor PEBs considering wear level
rules") applied, there is only 1 (3 - FASTMAP_ANCHOR_PEBS[1] -
FASTMAP_NEXT_ANCHOR_PEBS[1]) free PEB to fill pool and wl_pool, after
filling pool, wl_pool is always empty. So, UBI could be stuck in an
infinite loop:
ubi_thread system_wq
wear_leveling_worker <--------------------------------------------------
get_peb_for_wl |
// fm_wl_pool, used = size = 0 |
schedule_work(&ubi->fm_work) |
|
update_fastmap_work_fn |
ubi_update_fastmap |
ubi_refill_pools |
// ubi->free_count - ubi->beb_rsvd_pebs < 5 |
// wl_pool is not filled with any PEBs |
schedule_erase(old_fm_anchor) |
ubi_ensure_anchor_pebs |
__schedule_ubi_work(wear_leveling_worker) |
|
__erase_worker |
ensure_wear_leveling |
__schedule_ubi_work(wear_leveling_worker) --------------------------
, which cause high cpu usage of ubi_bgt:
top - 12:10:42 up 5 min, 2 users, load average: 1.76, 0.68, 0.27
Tasks: 123 total, 3 running, 54 sleeping, 0 stopped, 0 zombie
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
1589 root 20 0 0 0 0 R 45.0 0.0 0:38.86 ubi_bgt0d
319 root 20 0 0 0 0 I 15.2 0.0 0:15.29 kworker/0:3-eve
371 root 20 0 0 0 0 I 14.9 0.0 0:12.85 kworker/3:3-eve
20 root 20 0 0 0 0 I 11.3 0.0 0:05.33 kworker/1:0-eve
202 root 20 0 0 0 0 I 11.3 0.0 0:04.93 kworker/2:3-eve
In 4b68bf9a69d22dd ("ubi: Select fastmap anchor PEBs considering wear level
rules"), there are three key changes:
1) Choose the fastmap anchor when the most free PEBs are available.
2) Enable anchor move within the anchor area again as it is useful
for distributing wear.
3) Import a candidate fm anchor and check this PEB's erase count during
wear leveling. If the wear leveling limit is exceeded, use the used
anchor area PEB with the lowest erase count to replace it.
The anchor candidate can be removed, we can check fm_anchor PEB's erase
count during wear leveling. Fix it by:
1) Removing 'fm_next_anchor' and check 'fm_anchor' during wear leveling.
2) Preferentially filling one free peb into fm_wl_pool in condition of
ubi->free_count > ubi->beb_rsvd_pebs, then try to reserve enough
free count for fastmap non anchor pebs after the above prerequisites
are met.
Then, there are at least 1 PEB in pool and 1 PEB in wl_pool after calling
ubi_refill_pools() with all erase works done.
Fetch a reproducer in [Link].
Fixes: 4b68bf9a69d22dd ("ubi: Select fastmap anchor PEBs ... rules")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=215407
Signed-off-by: Zhihao Cheng <chengzhihao1 at huawei.com>
---
drivers/mtd/ubi/fastmap-wl.c | 63 +++++++++++++++++++++++-------------
drivers/mtd/ubi/fastmap.c | 11 -------
drivers/mtd/ubi/ubi.h | 4 +--
drivers/mtd/ubi/wl.c | 19 +++++------
4 files changed, 51 insertions(+), 46 deletions(-)
diff --git a/drivers/mtd/ubi/fastmap-wl.c b/drivers/mtd/ubi/fastmap-wl.c
index 28f55f9cf715..21ea5ca8270b 100644
--- a/drivers/mtd/ubi/fastmap-wl.c
+++ b/drivers/mtd/ubi/fastmap-wl.c
@@ -97,6 +97,27 @@ struct ubi_wl_entry *ubi_wl_get_fm_peb(struct ubi_device *ubi, int anchor)
return e;
}
+/*
+ * has_enough_free_count - whether ubi has enough free pebs to fill fm pools
+ * @ubi: UBI device description object
+ *
+ * This helper function checks whether there are enough free pebs (deducted
+ * by fastmap pebs) to fill fm_pool and fm_wl_pool, above rule works after
+ * there is at least one of free pebs is filled into fm_wl_pool.
+ */
+static bool has_enough_free_count(struct ubi_device *ubi)
+{
+ int fm_used = 0; // fastmap non anchor pebs.
+
+ if (!ubi->free.rb_node)
+ return false;
+
+ if (ubi->fm_wl_pool.size > 0 && !(ubi->ro_mode || ubi->fm_disabled))
+ fm_used = ubi->fm_size / ubi->leb_size - 1;
+
+ return ubi->free_count - ubi->beb_rsvd_pebs > fm_used;
+}
+
/**
* ubi_refill_pools - refills all fastmap PEB pools.
* @ubi: UBI device description object
@@ -120,21 +141,17 @@ void ubi_refill_pools(struct ubi_device *ubi)
wl_tree_add(ubi->fm_anchor, &ubi->free);
ubi->free_count++;
}
- if (ubi->fm_next_anchor) {
- wl_tree_add(ubi->fm_next_anchor, &ubi->free);
- ubi->free_count++;
- }
- /* All available PEBs are in ubi->free, now is the time to get
+ /*
+ * All available PEBs are in ubi->free, now is the time to get
* the best anchor PEBs.
*/
ubi->fm_anchor = ubi_wl_get_fm_peb(ubi, 1);
- ubi->fm_next_anchor = ubi_wl_get_fm_peb(ubi, 1);
for (;;) {
enough = 0;
if (pool->size < pool->max_size) {
- if (!ubi->free.rb_node)
+ if (!has_enough_free_count(ubi))
break;
e = wl_get_wle(ubi);
@@ -147,8 +164,7 @@ void ubi_refill_pools(struct ubi_device *ubi)
enough++;
if (wl_pool->size < wl_pool->max_size) {
- if (!ubi->free.rb_node ||
- (ubi->free_count - ubi->beb_rsvd_pebs < 5))
+ if (!has_enough_free_count(ubi))
break;
e = find_wl_entry(ubi, &ubi->free, WL_FREE_MAX_DIFF);
@@ -286,20 +302,26 @@ static struct ubi_wl_entry *get_peb_for_wl(struct ubi_device *ubi)
int ubi_ensure_anchor_pebs(struct ubi_device *ubi)
{
struct ubi_work *wrk;
+ struct ubi_wl_entry *anchor;
spin_lock(&ubi->wl_lock);
- /* Do we have a next anchor? */
- if (!ubi->fm_next_anchor) {
- ubi->fm_next_anchor = ubi_wl_get_fm_peb(ubi, 1);
- if (!ubi->fm_next_anchor)
- /* Tell wear leveling to produce a new anchor PEB */
- ubi->fm_do_produce_anchor = 1;
+ /* Do we already have an anchor? */
+ if (ubi->fm_anchor) {
+ spin_unlock(&ubi->wl_lock);
+ return 0;
}
- /* Do wear leveling to get a new anchor PEB or check the
- * existing next anchor candidate.
- */
+ /* See if we can find an anchor PEB on the list of free PEBs */
+ anchor = ubi_wl_get_fm_peb(ubi, 1);
+ if (anchor) {
+ ubi->fm_anchor = anchor;
+ spin_unlock(&ubi->wl_lock);
+ return 0;
+ }
+
+ ubi->fm_do_produce_anchor = 1;
+ /* No luck, trigger wear leveling to produce a new anchor PEB. */
if (ubi->wl_scheduled) {
spin_unlock(&ubi->wl_lock);
return 0;
@@ -381,11 +403,6 @@ static void ubi_fastmap_close(struct ubi_device *ubi)
ubi->fm_anchor = NULL;
}
- if (ubi->fm_next_anchor) {
- return_unused_peb(ubi, ubi->fm_next_anchor);
- ubi->fm_next_anchor = NULL;
- }
-
if (ubi->fm) {
for (i = 0; i < ubi->fm->used_blocks; i++)
kfree(ubi->fm->e[i]);
diff --git a/drivers/mtd/ubi/fastmap.c b/drivers/mtd/ubi/fastmap.c
index 01dcdd94c9d2..57fa60682d73 100644
--- a/drivers/mtd/ubi/fastmap.c
+++ b/drivers/mtd/ubi/fastmap.c
@@ -1205,17 +1205,6 @@ static int ubi_write_fastmap(struct ubi_device *ubi,
fm_pos += sizeof(*fec);
ubi_assert(fm_pos <= ubi->fm_size);
}
- if (ubi->fm_next_anchor) {
- fec = (struct ubi_fm_ec *)(fm_raw + fm_pos);
-
- fec->pnum = cpu_to_be32(ubi->fm_next_anchor->pnum);
- set_seen(ubi, ubi->fm_next_anchor->pnum, seen_pebs);
- fec->ec = cpu_to_be32(ubi->fm_next_anchor->ec);
-
- free_peb_count++;
- fm_pos += sizeof(*fec);
- ubi_assert(fm_pos <= ubi->fm_size);
- }
fmh->free_peb_count = cpu_to_be32(free_peb_count);
ubi_for_each_used_peb(ubi, wl_e, tmp_rb) {
diff --git a/drivers/mtd/ubi/ubi.h b/drivers/mtd/ubi/ubi.h
index 7c083ad58274..078112e23dfd 100644
--- a/drivers/mtd/ubi/ubi.h
+++ b/drivers/mtd/ubi/ubi.h
@@ -489,8 +489,7 @@ struct ubi_debug_info {
* @fm_work: fastmap work queue
* @fm_work_scheduled: non-zero if fastmap work was scheduled
* @fast_attach: non-zero if UBI was attached by fastmap
- * @fm_anchor: The new anchor PEB used during fastmap update
- * @fm_next_anchor: An anchor PEB candidate for the next time fastmap is updated
+ * @fm_anchor: The next anchor PEB to use for fastmap
* @fm_do_produce_anchor: If true produce an anchor PEB in wl
*
* @used: RB-tree of used physical eraseblocks
@@ -601,7 +600,6 @@ struct ubi_device {
int fm_work_scheduled;
int fast_attach;
struct ubi_wl_entry *fm_anchor;
- struct ubi_wl_entry *fm_next_anchor;
int fm_do_produce_anchor;
/* Wear-leveling sub-system's stuff */
diff --git a/drivers/mtd/ubi/wl.c b/drivers/mtd/ubi/wl.c
index 8455f1d47f3c..afcdacb9d0e9 100644
--- a/drivers/mtd/ubi/wl.c
+++ b/drivers/mtd/ubi/wl.c
@@ -689,16 +689,16 @@ static int wear_leveling_worker(struct ubi_device *ubi, struct ubi_work *wrk,
#ifdef CONFIG_MTD_UBI_FASTMAP
e1 = find_anchor_wl_entry(&ubi->used);
- if (e1 && ubi->fm_next_anchor &&
- (ubi->fm_next_anchor->ec - e1->ec >= UBI_WL_THRESHOLD)) {
+ if (e1 && ubi->fm_anchor &&
+ (ubi->fm_anchor->ec - e1->ec >= UBI_WL_THRESHOLD)) {
ubi->fm_do_produce_anchor = 1;
- /* fm_next_anchor is no longer considered a good anchor
- * candidate.
+ /*
+ * fm_anchor is no longer considered a good anchor.
* NULL assignment also prevents multiple wear level checks
* of this PEB.
*/
- wl_tree_add(ubi->fm_next_anchor, &ubi->free);
- ubi->fm_next_anchor = NULL;
+ wl_tree_add(ubi->fm_anchor, &ubi->free);
+ ubi->fm_anchor = NULL;
ubi->free_count++;
}
@@ -1085,12 +1085,13 @@ static int __erase_worker(struct ubi_device *ubi, struct ubi_work *wl_wrk)
if (!err) {
spin_lock(&ubi->wl_lock);
- if (!ubi->fm_disabled && !ubi->fm_next_anchor &&
+ if (!ubi->fm_disabled && !ubi->fm_anchor &&
e->pnum < UBI_FM_MAX_START) {
- /* Abort anchor production, if needed it will be
+ /*
+ * Abort anchor production, if needed it will be
* enabled again in the wear leveling started below.
*/
- ubi->fm_next_anchor = e;
+ ubi->fm_anchor = e;
ubi->fm_do_produce_anchor = 0;
} else {
wl_tree_add(e, &ubi->free);
--
2.31.1
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