On 3/30/20 10:54 PM, Richard Weinberger wrote:
On Mon, Jan 13, 2020 at 3:56 PM Arne Edholm <arne.edholm@xxxxxxxx> wrote:
>
> There is a risk that the fastmap anchor PEB is alternating between
> just two PEBs, the current anchor and the previous anchor that was just
> deleted. As the fastmap pools gets the first take on free PEBs, the
> pools may leave no free PEBs to be selected as the new anchor,
> resulting in the two PEBs alternating behaviour. If the anchor PEBs gets
> a high erase count the PEBs will not be used by the pools but remain in
> ubi->free, even more increasing the likelihood they will be used as
> anchors.
>
> Getting stuck using only a couple of PEBs continuously will result in an
> uneven wear, eventually leading to failure.
>
> To fix this:
>
> - Choose the fastmap anchor when the most free PEBs are available.
This is
> during rebuilding of the fastmap pools, after the unused pool PEBs are
> added to ubi->free but before the pools are populated again from the
> free PEBs. Also reserve an additional second best PEB as a candidate
> for the next time the fast map anchor is updated. If a better PEB is
> found the next time the fast map anchor is updated, the candidate is
> made available for building the pools.
>
> - Enable anchor move within the anchor area again as it is useful for
> distributing wear.
>
> - The anchor candidate for the next fastmap update is the most
suited free
> PEB. Check this PEB's erase count during wear leveling. If the wear
> leveling limit is exceeded, the PEB is considered unsuitable for
now. As
> all other non used anchor area PEBs should be even worse, free up the
> used anchor area PEB with the lowest erase count.
>
> Signed-off-by: Arne Edholm <arne.edholm@xxxxxxxx>
> ---
> drivers/mtd/ubi/fastmap-wl.c | 39
++++++++++++++++++++++++---------------
> drivers/mtd/ubi/fastmap.c | 11 +++++++++++
> drivers/mtd/ubi/ubi.h | 4 +++-
> drivers/mtd/ubi/wl.c | 28 +++++++++++++++++++---------
> 4 files changed, 57 insertions(+), 25 deletions(-)
>
> diff --git a/drivers/mtd/ubi/fastmap-wl.c b/drivers/mtd/ubi/fastmap-wl.c
> index 426820ab9afe..97cb57a12440 100644
> --- a/drivers/mtd/ubi/fastmap-wl.c
> +++ b/drivers/mtd/ubi/fastmap-wl.c
> @@ -110,6 +110,21 @@ void ubi_refill_pools(struct ubi_device *ubi)
> wl_pool->size = 0;
> pool->size = 0;
>
> + if (ubi->fm_anchor) {
> + 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
> + * 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) {
> @@ -265,26 +280,20 @@ 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 already have an anchor? */
> - if (ubi->fm_anchor) {
> - spin_unlock(&ubi->wl_lock);
> - return 0;
> - }
> -
> - /* 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;
> + /* 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;
> }
>
> - /* No luck, trigger wear leveling to produce a new anchor PEB */
> - ubi->fm_do_produce_anchor = 1;
> + /* Do wear leveling to get a new anchor PEB or check the
> + * existing next anchor candidate.
> + */
> if (ubi->wl_scheduled) {
> spin_unlock(&ubi->wl_lock);
> return 0;
> diff --git a/drivers/mtd/ubi/fastmap.c b/drivers/mtd/ubi/fastmap.c
> index 1c7be4eb3ba6..02332f9ea996 100644
> --- a/drivers/mtd/ubi/fastmap.c
> +++ b/drivers/mtd/ubi/fastmap.c
> @@ -1220,6 +1220,17 @@ 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 9688b411c930..a12fdb137fa4 100644
> --- a/drivers/mtd/ubi/ubi.h
> +++ b/drivers/mtd/ubi/ubi.h
> @@ -491,7 +491,8 @@ 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 next anchor PEB to use for 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_do_produce_anchor: If true produce an anchor PEB in wl
> *
> * @used: RB-tree of used physical eraseblocks
> @@ -602,6 +603,7 @@ 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 5d77a38dba54..804c434928aa 100644
> --- a/drivers/mtd/ubi/wl.c
> +++ b/drivers/mtd/ubi/wl.c
> @@ -688,20 +688,27 @@ 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)) {
> + ubi->fm_do_produce_anchor = 1;
> + /* fm_next_anchor is no longer considered a good anchor
> + * candidate.
> + * 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;
> + ubi->free_count++;
> + }
> +
> if (ubi->fm_do_produce_anchor) {
> - e1 = find_anchor_wl_entry(&ubi->used);
> if (!e1)
> goto out_cancel;
The logic here is a little strange. Why don't you check for e1 being
NULL in the new code block
above?
Failing to get e1 is not critical in the new above code, it just means
we skip the anchor wl check and continue what used to be done before
this change. e1 is required however when specifically tasked with
generating a new anchor, hence the placement of the NULL check.
> e2 = get_peb_for_wl(ubi);
> if (!e2)
> goto out_cancel;
>
> - /*
> - * Anchor move within the anchor area is useless.
> - */
> - if (e2->pnum < UBI_FM_MAX_START)
> - goto out_cancel;
> -
Are you sure we can drop this optimization?
I can't find a problem with this. An anchor area PEB (with high EC) in
the wl pool is consumed to make another anchor area PEB (lower EC) in
ubi->used available by processing it to ubi->free. This process should
be finished before fastmap update needs the PEB thanks to synchronous
delete and fm_eba_sem.
On the other hand, keeping your optimization doesn't break the
functionality of the new code either, the removal is just a small
optimization with regard to wear leveling. So if you are concerned it
can be kept. (If it is kept though, it needs to be modified to return e2
to ubi->free as right now it is leaked. But that would be a separate
patch as it is not tied to this change right?)
Other than that I like your approach and would merge it. :-)
Thank you!
> self_check_in_wl_tree(ubi, e1, &ubi->used);
> rb_erase(&e1->u.rb, &ubi->used);
> dbg_wl("anchor-move PEB %d to PEB %d", e1->pnum,
e2->pnum);
> @@ -1080,8 +1087,11 @@ static int __erase_worker(struct ubi_device
*ubi, struct ubi_work *wl_wrk)
> if (!err) {
> spin_lock(&ubi->wl_lock);
>
> - if (!ubi->fm_anchor && e->pnum < UBI_FM_MAX_START) {
> - ubi->fm_anchor = e;
> + if (!ubi->fm_next_anchor && e->pnum <
UBI_FM_MAX_START) {
> + /* Abort anchor production, if needed it will be
> + * enabled again in the wear leveling
started below.
> + */
> + ubi->fm_next_anchor = e;
> ubi->fm_do_produce_anchor = 0;
> } else {
> wl_tree_add(e, &ubi->free);
> --
> 2.11.0
>
>
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> http://lists.infradead.org/mailman/listinfo/linux-mtd/
--
Thanks,
//richard
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