Commit Graph

37 Commits

Author SHA1 Message Date
Igor Konopko
a96de64a24 lightnvm: pblk: simplify partial read path
This patch changes the approach to handling partial read path.

In old approach merging of data from round buffer and drive was fully
made by drive. This had some disadvantages - code was complex and
relies on bio internals, so it was hard to maintain and was strongly
dependent on bio changes.

In new approach most of the handling is done mostly by block layer
functions such as bio_split(), bio_chain() and generic_make request()
and generally is less complex and easier to maintain. Below some more
details of the new approach.

When read bio arrives, it is cloned for pblk internal purposes. All
the L2P mapping, which includes copying data from round buffer to bio
and thus bio_advance() calls is done on the cloned bio, so the original
bio is untouched. If we found that we have partial read case, we
still have original bio untouched, so we can split it and continue to
process only first part of it in current context, when the rest will be
called as separate bio request which is passed to generic_make_request()
for further processing.

Signed-off-by: Igor Konopko <igor.j.konopko@intel.com>
Reviewed-by: Heiner Litz <hlitz@ucsc.edu>
Reviewed-by: Javier González <javier@javigon.com>
Signed-off-by: Matias Bjørling <mb@lightnvm.io>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-05-06 10:19:19 -06:00
Igor Konopko
486b5aac85 lightnvm: pblk: fix lock order in pblk_rb_tear_down_check
In pblk_rb_tear_down_check() the spinlock functions are not
called in proper order.

Fixes: a4bd217 ("lightnvm: physical block device (pblk) target")
Signed-off-by: Igor Konopko <igor.j.konopko@intel.com>
Reviewed-by: Javier González <javier@javigon.com>
Reviewed-by: Hans Holmberg <hans.holmberg@cnexlabs.com>
Signed-off-by: Matias Bjørling <mb@lightnvm.io>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-05-06 10:19:18 -06:00
Heiner Litz
0586942f03 lightnvm: pblk: fix race condition on GC
This patch fixes a race condition where a write is mapped to the last
sectors of a line. The write is synced to the device but the L2P is not
updated yet. When the line is garbage collected before the L2P update
is performed, the sectors are ignored by the GC logic and the line is
freed before all sectors are moved. When the L2P is finally updated, it
contains a mapping to a freed line, subsequent reads of the
corresponding LBAs fail.

This patch introduces a per line counter specifying the number of
sectors that are synced to the device but have not been updated in the
L2P. Lines with a counter of greater than zero will not be selected
for GC.

Signed-off-by: Heiner Litz <hlitz@ucsc.edu>
Reviewed-by: Hans Holmberg <hans.holmberg@cnexlabs.com>
Reviewed-by: Javier González <javier@javigon.com>
Signed-off-by: Matias Bjørling <mb@lightnvm.io>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-02-11 08:18:08 -07:00
Javier González
b4cdc4260e lightnvm: pblk: prevent stall due to wb threshold
In order to respect mw_cuinits, pblk's write buffer maintains a
backpointer to protect data not yet persisted; when writing to the write
buffer, this backpointer defines a threshold that pblk's rate-limiter
enforces.

On small PU configurations, the following scenarios might take place: (i)
the threshold is larger than the write buffer and (ii) the threshold is
smaller than the write buffer, but larger than the maximun allowed
split bio - 256KB at this moment (Note that writes are not always
split - we only do this when we the size of the buffer is smaller
than the buffer). In both cases, pblk's rate-limiter prevents the I/O to
be written to the buffer, thus stalling.

This patch fixes the original backpointer implementation by considering
the threshold both on buffer creation and on the rate-limiters path,
when bio_split is triggered (case (ii) above).

Fixes: 766c8ceb16 ("lightnvm: pblk: guarantee that backpointer is respected on writer stall")
Signed-off-by: Javier González <javier@javigon.com>
Reviewed-by: Hans Holmberg <hans.holmberg@cnexlabs.com>
Signed-off-by: Matias Bjørling <mb@lightnvm.io>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2019-02-11 08:18:08 -07:00
Igor Konopko
55d8ec3539 lightnvm: pblk: support packed metadata
pblk performs recovery of open lines by storing the LBA in the per LBA
metadata field. Recovery therefore only works for drives that has this
field.

This patch adds support for packed metadata, which store l2p mapping
for open lines in last sector of every write unit and enables drives
without per IO metadata to recover open lines.

After this patch, drives with OOB size <16B will use packed metadata
and metadata size larger than16B will continue to use the device per
IO metadata.

Reviewed-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Igor Konopko <igor.j.konopko@intel.com>
Signed-off-by: Matias Bjørling <mb@lightnvm.io>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-12-11 12:22:35 -07:00
Hua Su
6e82f0ba00 lightnvm: pblk: fix spelling in comment
Signed-off-by: Hua Su <suhua.tanke@gmail.com>
Updated description.
Signed-off-by: Matias Bjørling <mb@lightnvm.io>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-12-11 12:22:34 -07:00
Javier González
766c8ceb16 lightnvm: pblk: guarantee that backpointer is respected on writer stall
pblk's write buffer must guarantee that it respects the device's
constrains for reads (i.e., mw_cunits). This is done by maintaining a
backpointer that updates the L2P table as entries wrap up, making them
point to the media instead of pointing to the write buffer.

This mechanism can race in case that the write thread stalls, as the
write pointer will protect the last written entry, thus disregarding the
read constrains.

This patch adds an extra check on wrap up, making sure that the
threshold is respected at all times, preventing new entries to overwrite
committed data, also in case of write thread stall.

Reported-by: Heiner Litz <hlitz@ucsc.edu>
Signed-off-by: Javier González <javier@cnexlabs.com>
Reviewed-by: Heiner Litz <hlitz@ucsc.edu>
Signed-off-by: Matias Bjørling <mb@lightnvm.io>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-10-09 08:25:08 -06:00
Javier González
9bd1f875c0 lightnvm: pblk: move ring buffer alloc/free rb init
pblk's read/write buffer currently takes a buffer and its size and uses
it to create the metadata around it to use it as a ring buffer. This
puts the responsibility of allocating/freeing ring buffer memory on the
ring buffer user. Instead, move it inside of the ring buffer helpers
(pblk-rb.c). This simplifies creation/destruction routines.

Signed-off-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <mb@lightnvm.io>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-10-09 08:25:08 -06:00
Javier González
40b8657dcc lightnvm: pblk: encapsulate rb pointer operations
pblk's read/write buffer is always a power-of-2, thus wrapping up the
buffer can be done with a bit mask. Since this is an implementation
detail internal to the write buffer, make a helper that hides pointer
increment + wrap, and allows to transparently relax this assumption in
the future.

Signed-off-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <mb@lightnvm.io>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-10-09 08:25:08 -06:00
Javier González
dde4aac20b lightnvm: pblk: remove unused function
Removed unused function in pblk-rb.c

Signed-off-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <mb@lightnvm.io>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-10-09 08:25:08 -06:00
Javier González
02a1520d56 lightnvm: pblk: add SPDX license tag
Add GLP-2.0 SPDX license tag to all pblk files

Signed-off-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <mb@lightnvm.io>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-10-09 08:25:08 -06:00
Javier González
cb21665c8d lightnvm: pblk: improve line helpers
The current helper to obtain a line from a ppa returns the line id,
which requires its users to explicitly retrieve the pointer to the line
with the id.

Make 2 different helpers: one returning the line id and one returning
the line directly.

Signed-off-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <mb@lightnvm.io>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-10-09 08:25:06 -06:00
Matias Bjørling
4e495a46b1 lightnvm: pblk: expose generic disk name on pr_* msgs
The error messages in pblk does not say which pblk instance that
a message occurred from. Update each error message to reflect the
instance it belongs to, and also prefix it with pblk, so we know
the message comes from the pblk module.

Signed-off-by: Matias Bjørling <mb@lightnvm.io>
Reviewed-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-07-13 08:14:43 -06:00
Matias Bjørling
880eda5440 lightnvm: move NVM_DEBUG to pblk
There is no users of CONFIG_NVM_DEBUG in the LightNVM subsystem. All
users are in pblk. Rename NVM_DEBUG to NVM_PBLK_DEBUG and enable
only for pblk.

Also fix up the CONFIG_NVM_PBLK entry to follow the code style for
Kconfig files.

Signed-off-by: Matias Bjørling <mb@lightnvm.io>
Reviewed-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-07-13 08:14:31 -06:00
Mauro Carvalho Chehab
5fb94e9ca3 docs: Fix some broken references
As we move stuff around, some doc references are broken. Fix some of
them via this script:
	./scripts/documentation-file-ref-check --fix

Manually checked if the produced result is valid, removing a few
false-positives.

Acked-by: Takashi Iwai <tiwai@suse.de>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Acked-by: Stephen Boyd <sboyd@kernel.org>
Acked-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Acked-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Reviewed-by: Coly Li <colyli@suse.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Acked-by: Jonathan Corbet <corbet@lwn.net>
2018-06-15 18:10:01 -03:00
Hans Holmberg
cc9c9a00b1 lightnvm: pblk: kick writer on new flush points
Unless we kick the writer directly when setting a new flush point, the
user risks having to wait for up to one second (the default timeout for
the write thread to be kicked) for the IO to complete.

Signed-off-by: Hans Holmberg <hans.holmberg@cnexlabs.com>
Signed-off-by: Matias Bjørling <mb@lightnvm.io>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-06-01 09:02:53 -06:00
Hans Holmberg
6a3abf5bee lightnvm: pblk: rework write error recovery path
The write error recovery path is incomplete, so rework
the write error recovery handling to do resubmits directly
from the write buffer.

When a write error occurs, the remaining sectors in the chunk are
mapped out and invalidated and the request inserted in a resubmit list.

The writer thread checks if there are any requests to resubmit,
scans and invalidates any lbas that have been overwritten by later
writes and resubmits the failed entries.

Signed-off-by: Hans Holmberg <hans.holmberg@cnexlabs.com>
Reviewed-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <mb@lightnvm.io>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-06-01 09:02:53 -06:00
Javier González
e37d07983a lightnvm: pblk: warn in case of corrupted write buffer
When cleaning up buffer entries as we wrap up, their state should be
"completed". If any of the entries is in "submitted" state, it means
that something bad has happened. Trigger a warning immediately instead of
waiting for the state flag to eventually be updated, thus hiding the
issue.

Signed-off-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <mb@lightnvm.io>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-06-01 07:43:53 -06:00
Hans Holmberg
3c05ef115c lightnvm: pblk: prevent race in pblk_rb_flush_point_set
Make sure that we are not advancing the sync pointer while
we're adding bios to the write buffer entry completion list.

This race condition results in bios not completing and was identified
by a hang when running xfstest generic/113.

Signed-off-by: Hans Holmberg <hans.holmberg@cnexlabs.com>
Reviewed-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <mb@lightnvm.io>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-03-29 17:29:09 -06:00
Hans Holmberg
5d149bfabe lightnvm: pblk: add padding distribution sysfs attribute
When pblk receives a sync, all data up to that point in the write buffer
must be comitted to persistent storage, and as flash memory comes with a
minimal write size there is a significant cost involved both in terms
of time for completing the sync and in terms of write amplification
padded sectors for filling up to the minimal write size.

In order to get a better understanding of the costs involved for syncs,
Add a sysfs attribute to pblk: padded_dist, showing a normalized
distribution of sectors padded. In order to facilitate measurements of
specific workloads during the lifetime of the pblk instance, the
distribution can be reset by writing 0 to the attribute.

Do this by introducing counters for each possible padding:
{0..(minimal write size - 1)} and calculate the normalized distribution
when showing the attribute.

Signed-off-by: Hans Holmberg <hans.holmberg@cnexlabs.com>
Signed-off-by: Javier González <javier@cnexlabs.com>
Rearranged total_buckets statement in pblk_sysfs_get_padding_dist
Signed-off-by: Matias Bjørling <mb@lightnvm.io>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-03-29 17:29:09 -06:00
Hans Holmberg
76758390f8 lightnvm: pblk: export write amplification counters to sysfs
In a SSD, write amplification, WA, is defined as the average
number of page writes per user page write. Write amplification
negatively affects write performance and decreases the lifetime
of the disk, so it's a useful metric to add to sysfs.

In plkb's case, the number of writes per user sector is the sum of:

    (1) number of user writes
    (2) number of sectors written by the garbage collector
    (3) number of sectors padded (i.e. due to syncs)

This patch adds persistent counters for 1-3 and two sysfs attributes
to export these along with WA calculated with five decimals:

    write_amp_mileage: the accumulated write amplification stats
                      for the lifetime of the pblk instance

    write_amp_trip: resetable stats to facilitate delta measurements,
                    values reset at creation and if 0 is written
                    to the attribute.

64-bit counters are used as a 32 bit counter would wrap around
already after about 17 TB worth of user data. It will take a
long long time before the 64 bit sector counters wrap around.

The counters are stored after the bad block bitmap in the first
emeta sector of each written line. There is plenty of space in the
first emeta sector, so we don't need to bump the major version of
the line data format.

Signed-off-by: Hans Holmberg <hans.holmberg@cnexlabs.com>
Signed-off-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <mb@lightnvm.io>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-03-29 17:29:09 -06:00
Hans Holmberg
b36bbf9d4f lightnvm: pblk: prevent premature sync point resets
Unless we protect flush pointer updates with a lock, we risk
resetting new flush points before we've synced all sectors
up to that point.

This patch protects new flush points with the same spin lock
that is being held when advancing the sync pointer and
resetting completed flush points.

Signed-off-by: Hans Holmberg <hans.holmberg@cnexlabs.com>
Signed-off-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <m@bjorling.me>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-01-05 08:50:12 -07:00
Hans Holmberg
533657c190 lightnvm: pblk: clear flush point on completed writes
Move completion of syncs and clearing of flush points to the
write completion path - this ensures that the data has been
comitted to the media before completing bios containing syncs.

Signed-off-by: Hans Holmberg <hans.holmberg@cnexlabs.com>
Signed-off-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <m@bjorling.me>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-01-05 08:50:12 -07:00
Hans Holmberg
8154d296d9 lightnvm: pblk: rename sync_point to flush_point
Sync point is a really confusing name for keeping track of
the last entry that needs to be flushed so change the name
to to flush_point instead.

Signed-off-by: Hans Holmberg <hans.holmberg@cnexlabs.com>
Signed-off-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <m@bjorling.me>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-01-05 08:50:12 -07:00
Javier González
b1bcfda105 lightnvm: pblk: compress and reorder helper functions
Through time, we have generated some redundant helper functions.
Refactor them to eliminate redundant and unnecessary code. Also, reorder
them to improve readability

Signed-off-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <m@bjorling.me>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2018-01-05 08:50:12 -07:00
Rakesh Pandit
05ed344769 lightnvm: pblk: reduce arguments in __pblk_rb_update_l2p
We already pass the structure pointer so no need to pass the member.

Signed-off-by: Rakesh Pandit <rakesh@tuxera.com>
Signed-off-by: Matias Bjørling <m@bjorling.me>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2017-10-13 08:34:57 -06:00
Javier González
875d94f3a4 lightnvm: pblk: allocate bio size more accurately
Wait until we know the exact number of ppas to be sent to the device,
before allocating the bio.

Signed-off-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <m@bjorling.me>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2017-10-13 08:34:57 -06:00
Javier González
6ca2f71f3e lightnvm: pblk: simplify path on REQ_PREFLUSH
On REQ_PREFLUSH, directly tag the I/O context flags to signal a flush in
the write to cache path, instead of finding the correct entry context
and imposing a memory barrier. This simplifies the code and might
potentially prevent race conditions when adding functionality to the
write path.

Signed-off-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <m@bjorling.me>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2017-10-13 08:34:57 -06:00
Javier González
d340121eb7 lightnvm: pblk: simplify data validity check on GC
When a line is selected for recycling by the garbage collector (GC), the
line state changes and the invalid bitmap is frozen, preventing
invalidations from happening. Throughout the GC, the L2P map is checked
to verify that not data being recycled has been updated. The last check
is done before the new map is being stored on the L2P table. Though
this algorithm works, it requires a number of corner cases to be checked
each time the L2P table is being updated. This complicates readability
and is error prone in case that the recycling algorithm is modified.

Instead, this patch makes the invalid bitmap accessible even when the
line is being recycled. When recycled data is being remapped, it is
enough to check the invalid bitmap for the line before updating the L2P
table.

Signed-off-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <m@bjorling.me>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2017-10-13 08:34:57 -06:00
Javier González
75cb8e939c lightnvm: pblk: advance bio according to lba index
When a lba either hits the cache or corresponds to an empty entry in the
L2P table, we need to advance the bio according to the position in which
the lba is located. Otherwise, we will copy data in the wrong page, thus
causing data corruption for the application.

In case of a cache hit, we assumed that bio->bi_iter.bi_idx would
contain the correct index, but this is no necessarily true. Instead, use
the local bio advance counter and iterator. This guarantees that lbas
hitting the cache are copied into the right bv_page.

In case of an empty L2P entry, we omitted to advance the bio. In the
cases when the same I/O also contains a cache hit, data corresponding
to this lba will be copied to the wrong bv_page. Fix this by advancing
the bio as we do in the case of a cache hit.

Fixes: a4bd217b43 lightnvm: physical block device (pblk) target

Signed-off-by: Javier González <javier@javigon.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2017-07-28 08:06:00 -06:00
Javier González
076984669d lightnvm: pblk: verify that cache read is still valid
When a read is directed to the cache, we risk that the lba has been
updated during the time we made the L2P table lookup and the time we are
actually reading form the cache. We intentionally not hold the L2P lock
not to block other threads.

While strict ordering is not a guarantee at this level (unless REQ_FLUSH
has been previously issued), we have experience that some databases that
have recently implemented direct I/O support, issue metadata reads very
close to the writes, without issuing a fsync in the middle. An easy way
to support them while they is to make an extra effort and check the L2P
map right before reading the cache.

Signed-off-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <matias@cnexlabs.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2017-06-30 11:08:18 -06:00
Javier González
ee8d5c1ad5 lightnvm: pblk: remove target using async. I/Os
When removing a pblk instance, pad the current line using asynchronous
I/O. This reduces the removal time from ~1 minute in the worst case to a
couple of seconds.

Signed-off-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <matias@cnexlabs.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2017-06-30 11:08:18 -06:00
Javier González
1088812978 lightnvm: pblk: schedule if data is not ready
When user threads place data into the write buffer, they reserve space
and do the memory copy out of the lock. As a consequence, when the write
thread starts persisting data, there is a chance that it is not copied
yet. In this case, avoid polling, and schedule before retrying.

Signed-off-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <matias@cnexlabs.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2017-06-30 11:08:18 -06:00
Javier González
588726d3ec lightnvm: pblk: fail gracefully on irrec. error
Due to user writes being decoupled from media writes because of the need
of an intermediate write buffer, irrecoverable media write errors lead
to pblk stalling; user writes fill up the buffer and end up in an
infinite retry loop.

In order to let user writes fail gracefully, it is necessary for pblk to
keep track of its own internal state and prevent further writes from
being placed into the write buffer.

This patch implements a state machine to keep track of internal errors
and, in case of failure, fail further user writes in an standard way.
Depending on the type of error, pblk will do its best to persist
buffered writes (which are already acknowledged) and close down on a
graceful manner. This way, data might be recovered by re-instantiating
pblk. Such state machine paves out the way for a state-based FTL log.

Signed-off-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <matias@cnexlabs.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2017-06-26 16:27:39 -06:00
Javier González
b20ba1bc74 lightnvm: pblk: redesign GC algorithm
At the moment, in order to get enough read parallelism, we have recycled
several lines at the same time. This approach has proven not to work
well when reaching capacity, since we end up mixing valid data from all
lines, thus not maintaining a sustainable free/recycled line ratio.

The new design, relies on a two level workqueue mechanism. In the first
level, we read the metadata for a number of lines based on the GC list
they reside on (this is governed by the number of valid sectors in each
line). In the second level, we recycle a single line at a time. Here, we
issue reads in parallel, while a single GC write thread places data in
the write buffer. This design allows to (i) only move data from one line
at a time, thus maintaining a sane free/recycled ration and (ii)
maintain the GC writer busy with recycled data.

Signed-off-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <matias@cnexlabs.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2017-06-26 16:27:39 -06:00
Javier González
d624f371d5 lightnvm: pblk: generalize erase path
Erase I/Os are scheduled with the following goals in mind: (i) minimize
LUNs collisions with write I/Os, and (ii) even out the price of erasing
on every write, instead of putting all the burden on when garbage
collection runs. This works well on the current design, but is specific
to the default mapping algorithm.

This patch generalizes the erase path so that other mapping algorithms
can select an arbitrary line to be erased instead. It also gets rid of
the erase semaphore since it creates jittering for user writes.

Signed-off-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <matias@cnexlabs.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
2017-06-26 16:24:53 -06:00
Javier González
a4bd217b43 lightnvm: physical block device (pblk) target
This patch introduces pblk, a host-side translation layer for
Open-Channel SSDs to expose them like block devices. The translation
layer allows data placement decisions, and I/O scheduling to be
managed by the host, enabling users to optimize the SSD for their
specific workloads.

An open-channel SSD has a set of LUNs (parallel units) and a
collection of blocks. Each block can be read in any order, but
writes must be sequential. Writes may also fail, and if a block
requires it, must also be reset before new writes can be
applied.

To manage the constraints, pblk maintains a logical to
physical address (L2P) table,  write cache, garbage
collection logic, recovery scheme, and logic to rate-limit
user I/Os versus garbage collection I/Os.

The L2P table is fully-associative and manages sectors at a
4KB granularity. Pblk stores the L2P table in two places, in
the out-of-band area of the media and on the last page of a
line. In the cause of a power failure, pblk will perform a
scan to recover the L2P table.

The user data is organized into lines. A line is data
striped across blocks and LUNs. The lines enable the host to
reduce the amount of metadata to maintain besides the user
data and makes it easier to implement RAID or erasure coding
in the future.

pblk implements multi-tenant support and can be instantiated
multiple times on the same drive. Each instance owns a
portion of the SSD - both regarding I/O bandwidth and
capacity - providing I/O isolation for each case.

Finally, pblk also exposes a sysfs interface that allows
user-space to peek into the internals of pblk. The interface
is available at /dev/block/*/pblk/ where * is the block
device name exposed.

This work also contains contributions from:
  Matias Bjørling <matias@cnexlabs.com>
  Simon A. F. Lund <slund@cnexlabs.com>
  Young Tack Jin <youngtack.jin@gmail.com>
  Huaicheng Li <huaicheng@cs.uchicago.edu>

Signed-off-by: Javier González <javier@cnexlabs.com>
Signed-off-by: Matias Bjørling <matias@cnexlabs.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
2017-04-16 10:06:33 -06:00