lkml.org 
[lkml]   [2018]   [Jun]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [PATCH] lightnvm: pblk: recover chunk state on 1.2 devices
Date
> On 29 Jun 2018, at 13.14, Matias Bjørling <mb@lightnvm.io> wrote:
>
> On 06/28/2018 11:12 AM, Javier González wrote:
>> The Open-Channel 1.2 spec does not define a mechanism for the host to
>> recover the block (chunk) state. As a consequence, a newly format device
>> will need to reconstruct the state. Currently, pblk assumes that blocks
>> are not erased, which might cause double-erases in case that the device
>> does not protect itself against them (which is not specified in the spec
>> either).
>
> It should not be specified in the spec. It is up to the device to handle
> double erases and not do it.
>
>> This patch, reconstructs the state based on read errors. If the first
>> sector of a block returns and empty page (NVM_RSP_ERR_EMPTYPAGE), then
>> the block s marked free, i.e., erased and ready to be used
>> (NVM_CHK_ST_FREE). Otherwise, the block is marked as closed
>> (NVM_CHK_ST_CLOSED). Note that even if a block is open and not fully
>> written, it has to be erased in order to be used again.
>
> Should we extend it to do the scan, and update the write pointer as
> well? I think this kind of feature already is baked into pblk?
>

This is already in place: we scan until empty page and take it from
there. This patch is only for the case in which we start a pblk instance
form scratch. On a device already owned by pblk, we would not have the
problem we are trying to solve here because we know the state.

>> One caveat of this approach is that blocks that have been erased at a
>> moment in time, will always be considered as erased. However, some media
>> might become unstable if blocks are not erased before usage. Since pblk
>> would follow this principle after the state of all blocks fall under
>> pblk's domain, we can consider this as an initialization problem. The
>> trade-off would be to fall back to the old behavior and risk premature
>> media wearing.
>
> The above is up to the device implementation to handle. We cannot
> expect users to understand the intrinsics of media.
>

Of course. The point is that with this approach, erases are left a bit
in the air and "preventable" write errors might happen, with the previous
the burden was put on the device to deal with double erases. It's a
tradeoff that I want to make clear before the path is taken.

>> Signed-off-by: Javier González <javier@cnexlabs.com>
>> ---
>> drivers/lightnvm/pblk-init.c | 138 ++++++++++++++++++++++++++++++++++++++-----
>> 1 file changed, 124 insertions(+), 14 deletions(-)
>> diff --git a/drivers/lightnvm/pblk-init.c b/drivers/lightnvm/pblk-init.c
>> index 3b8aa4a64cac..ce25f1473d8e 100644
>> --- a/drivers/lightnvm/pblk-init.c
>> +++ b/drivers/lightnvm/pblk-init.c
>> @@ -697,47 +697,138 @@ static void pblk_set_provision(struct pblk *pblk, long nr_free_blks)
>> atomic_set(&pblk->rl.free_user_blocks, nr_free_blks);
>> }
>> +static void pblk_state_complete(struct kref *ref)
>> +{
>> + struct pblk_pad_rq *pad_rq = container_of(ref, struct pblk_pad_rq, ref);
>> +
>> + complete(&pad_rq->wait);
>> +}
>> +
>> +static void pblk_end_io_state(struct nvm_rq *rqd)
>> +{
>> + struct pblk_pad_rq *pad_rq = rqd->private;
>> + struct pblk *pblk = pad_rq->pblk;
>> + struct nvm_tgt_dev *dev = pblk->dev;
>> + struct nvm_geo *geo = &dev->geo;
>> + struct pblk_line *line;
>> + struct nvm_chk_meta *chunk;
>> + int pos;
>> +
>> + line = &pblk->lines[pblk_ppa_to_line(rqd->ppa_addr)];
>> + pos = pblk_ppa_to_pos(geo, rqd->ppa_addr);
>> +
>> + chunk = &line->chks[pos];
>> +
>> + if (rqd->error == NVM_RSP_ERR_EMPTYPAGE)
>> + chunk->state = NVM_CHK_ST_FREE;
>> + else
>> + chunk->state = NVM_CHK_ST_CLOSED;
>> +
>> + bio_put(rqd->bio);
>> + pblk_free_rqd(pblk, rqd, PBLK_READ);
>> + kref_put(&pad_rq->ref, pblk_state_complete);
>> +}
>> +
>> +static int pblk_check_chunk_state(struct pblk *pblk, struct nvm_chk_meta *chunk,
>> + struct ppa_addr ppa, struct pblk_pad_rq *pad_rq)
>> +{
>> + struct nvm_rq *rqd;
>> + struct bio *bio;
>> + int ret;
>> +
>> + bio = bio_alloc(GFP_KERNEL, 1);
>> +
>> + if (pblk_bio_add_pages(pblk, bio, GFP_KERNEL, 1))
>> + goto fail_free_bio;
>> +
>> + rqd = pblk_alloc_rqd(pblk, PBLK_READ);
>> +
>> + rqd->bio = bio;
>> + rqd->opcode = NVM_OP_PREAD;
>> + rqd->flags = pblk_set_read_mode(pblk, PBLK_READ_SEQUENTIAL);
>> + rqd->nr_ppas = 1;
>> + rqd->ppa_addr = ppa;
>> + rqd->end_io = pblk_end_io_state;
>> + rqd->private = pad_rq;
>> +
>> + kref_get(&pad_rq->ref);
>> +
>> + ret = pblk_submit_io(pblk, rqd);
>> + if (ret) {
>> + pr_err("pblk: I/O submissin failed: %d\n", ret);
>> + goto fail_free_rqd;
>> + }
>> +
>> + return NVM_IO_OK;
>> +
>> +fail_free_rqd:
>> + pblk_free_rqd(pblk, rqd, PBLK_READ);
>> + pblk_bio_free_pages(pblk, bio, 0, bio->bi_vcnt);
>> +fail_free_bio:
>> + bio_put(bio);
>> +
>> + return NVM_IO_ERR;
>> +}
>> +
>> static int pblk_setup_line_meta_12(struct pblk *pblk, struct pblk_line *line,
>> void *chunk_meta)
>> {
>> struct nvm_tgt_dev *dev = pblk->dev;
>> struct nvm_geo *geo = &dev->geo;
>> struct pblk_line_meta *lm = &pblk->lm;
>> + struct pblk_pad_rq *pad_rq;
>> int i, chk_per_lun, nr_bad_chks = 0;
>> + pad_rq = kmalloc(sizeof(struct pblk_pad_rq), GFP_KERNEL);
>> + if (!pad_rq)
>> + return -1;
>> +
>> + pad_rq->pblk = pblk;
>> + init_completion(&pad_rq->wait);
>> + kref_init(&pad_rq->ref);
>> +
>> chk_per_lun = geo->num_chk * geo->pln_mode;
>> for (i = 0; i < lm->blk_per_line; i++) {
>> struct pblk_lun *rlun = &pblk->luns[i];
>> struct nvm_chk_meta *chunk;
>> - int pos = pblk_ppa_to_pos(geo, rlun->bppa);
>> + struct ppa_addr ppa = rlun->bppa;
>> + int pos = pblk_ppa_to_pos(geo, ppa);
>> u8 *lun_bb_meta = chunk_meta + pos * chk_per_lun;
>> chunk = &line->chks[pos];
>> - /*
>> - * In 1.2 spec. chunk state is not persisted by the device. Thus
>> - * some of the values are reset each time pblk is instantiated,
>> - * so we have to assume that the block is closed.
>> - */
>> - if (lun_bb_meta[line->id] == NVM_BLK_T_FREE)
>> - chunk->state = NVM_CHK_ST_CLOSED;
>> - else
>> - chunk->state = NVM_CHK_ST_OFFLINE;
>> -
>> chunk->type = NVM_CHK_TP_W_SEQ;
>> chunk->wi = 0;
>> chunk->slba = -1;
>> chunk->cnlb = geo->clba;
>> chunk->wp = 0;
>> - if (!(chunk->state & NVM_CHK_ST_OFFLINE))
>> + if (lun_bb_meta[line->id] != NVM_BLK_T_FREE) {
>> + chunk->state = NVM_CHK_ST_OFFLINE;
>> + set_bit(pos, line->blk_bitmap);
>> + nr_bad_chks++;
>> +
>> continue;
>> + }
>> - set_bit(pos, line->blk_bitmap);
>> - nr_bad_chks++;
>> + /*
>> + * In 1.2 spec. chunk state is not persisted by the device.
>> + * Recover the state based on media response.
>> + */
>> + ppa.g.blk = line->id;
>> + pblk_check_chunk_state(pblk, chunk, ppa, pad_rq);
>> }
>> + kref_put(&pad_rq->ref, pblk_state_complete);
>> +
>> + if (!wait_for_completion_io_timeout(&pad_rq->wait,
>> + msecs_to_jiffies(PBLK_COMMAND_TIMEOUT_MS))) {
>> + pr_err("pblk: state recovery timed out\n");
>> + return -1;
>> + }
>> +
>> + kfree(pad_rq);
>> return nr_bad_chks;
>> }
>> @@ -1036,6 +1127,23 @@ static int pblk_line_meta_init(struct pblk *pblk)
>> return 0;
>> }
>> +static void check_meta(struct pblk *pblk, struct pblk_line *line)
>> +{
>> + struct nvm_tgt_dev *dev = pblk->dev;
>> + struct nvm_geo *geo = &dev->geo;
>> + struct pblk_line_meta *lm = &pblk->lm;
>> + int i;
>> +
>> + for (i = 0; i < lm->blk_per_line; i++) {
>> + struct pblk_lun *rlun = &pblk->luns[i];
>> + struct nvm_chk_meta *chunk;
>> + struct ppa_addr ppa = rlun->bppa;
>> + int pos = pblk_ppa_to_pos(geo, ppa);
>> +
>> + chunk = &line->chks[pos];
>> + }
>> +}
>> +
>> static int pblk_lines_init(struct pblk *pblk)
>> {
>> struct pblk_line_mgmt *l_mg = &pblk->l_mg;
>> @@ -1077,6 +1185,8 @@ static int pblk_lines_init(struct pblk *pblk)
>> goto fail_free_lines;
>> nr_free_chks += pblk_setup_line_meta(pblk, line, chunk_meta, i);
>> +
>> + check_meta(pblk, line);
>> }
>> if (!nr_free_chks) {
>
> I'm okay with us doing this in pblk for now. Over time, someone may do
> the work move this (and other specific only-1.2/2.0 stuff) into the
> lightnvm subsystem. I don't think pblk should need to care about
> either 1.2 or 2.0.

That would be ideal.

Thanks!
[unhandled content-type:application/pgp-signature]
\
 
 \ /
  Last update: 2018-06-29 13:24    [W:0.069 / U:12.664 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site