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lightnvm: pblk: enable 1 LUN configuration

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Metadata I/Os are scheduled to minimize their impact on user data I/Os.
When there are enough LUNs instantiated (i.e., enough bandwidth), it is
easy to interleave metadata and data one after the other so that
metadata I/Os are the ones being blocked and not vice-versa.

We do this by calculating the distance between the I/Os in terms of the
LUNs that are not in used, and selecting a free LUN that satisfies a
the simple heuristic that metadata is scheduled behind. The per-LUN
semaphores guarantee consistency. This works fine on >1 LUN
configuration. However, when a single LUN is instantiated, this design
leads to a deadlock, where metadata waits to be scheduled on a free LUN.

This patch implements the 1 LUN case by simply scheduling the metadada
I/O after the data I/O. In the process, we refactor the way a line is
replaced to ensure that metadata writes are submitted after data writes
in order to guarantee block sequentiality. Note that, since there is
only one LUN, both I/Os will block each other by design. However, such
configuration only pursues tight read latencies, not write bandwidth.

Signed-off-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <m@bjorling.me>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Javier González
2017-10-13 14:46:26 +02:00
committed by Jens Axboe
parent 1e82123da6
commit 21d2287119
4 changed files with 29 additions and 19 deletions
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21
drivers/lightnvm/pblk-map.c
View File

@@ -25,13 +25,23 @@ static void pblk_map_page_data(struct pblk *pblk, unsigned int sentry,
unsigned int valid_secs)
{
struct pblk_line *line = pblk_line_get_data(pblk);
struct pblk_emeta *emeta = line->emeta;
struct pblk_emeta *emeta;
struct pblk_w_ctx *w_ctx;
__le64 *lba_list = emeta_to_lbas(pblk, emeta->buf);
__le64 *lba_list;
u64 paddr;
int nr_secs = pblk->min_write_pgs;
int i;
if (pblk_line_is_full(line)) {
struct pblk_line *prev_line = line;
line = pblk_line_replace_data(pblk);
pblk_line_close_meta(pblk, prev_line);
}
emeta = line->emeta;
lba_list = emeta_to_lbas(pblk, emeta->buf);
paddr = pblk_alloc_page(pblk, line, nr_secs);
for (i = 0; i < nr_secs; i++, paddr++) {
@@ -60,13 +70,6 @@ static void pblk_map_page_data(struct pblk *pblk, unsigned int sentry,
}
}
if (pblk_line_is_full(line)) {
struct pblk_line *prev_line = line;
pblk_line_replace_data(pblk);
pblk_line_close_meta(pblk, prev_line);
}
pblk_down_rq(pblk, ppa_list, nr_secs, lun_bitmap);
}