Commit 48debafe authored by Mikulas Patocka's avatar Mikulas Patocka Committed by Mike Snitzer
Browse files

dm: add writecache target



The writecache target caches writes on persistent memory or SSD.
It is intended for databases or other programs that need extremely low
commit latency.

The writecache target doesn't cache reads because reads are supposed to
be cached in page cache in normal RAM.

If persistent memory isn't available this target can still be used in
SSD mode.
Signed-off-by: default avatarMikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Colin Ian King <colin.king@canonical.com> # fix missing goto
Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com> # fix compilation issue with !DAX
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com> # use msecs_to_jiffies
Acked-by: Dan Williams <dan.j.williams@intel.com> # reworks to unify ARM and x86 flushing
Signed-off-by: default avatarMike Snitzer <msnitzer@redhat.com>
parent 72d711c8
The writecache target caches writes on persistent memory or on SSD. It
doesn't cache reads because reads are supposed to be cached in page cache
in normal RAM.
When the device is constructed, the first sector should be zeroed or the
first sector should contain valid superblock from previous invocation.
Constructor parameters:
1. type of the cache device - "p" or "s"
p - persistent memory
s - SSD
2. the underlying device that will be cached
3. the cache device
4. block size (4096 is recommended; the maximum block size is the page
size)
5. the number of optional parameters (the parameters with an argument
count as two)
high_watermark n (default: 50)
start writeback when the number of used blocks reach this
watermark
low_watermark x (default: 45)
stop writeback when the number of used blocks drops below
this watermark
writeback_jobs n (default: unlimited)
limit the number of blocks that are in flight during
writeback. Setting this value reduces writeback
throughput, but it may improve latency of read requests
autocommit_blocks n (default: 64 for pmem, 65536 for ssd)
when the application writes this amount of blocks without
issuing the FLUSH request, the blocks are automatically
commited
autocommit_time ms (default: 1000)
autocommit time in milliseconds. The data is automatically
commited if this time passes and no FLUSH request is
received
fua (by default on)
applicable only to persistent memory - use the FUA flag
when writing data from persistent memory back to the
underlying device
nofua
applicable only to persistent memory - don't use the FUA
flag when writing back data and send the FLUSH request
afterwards
- some underlying devices perform better with fua, some
with nofua. The user should test it
Status:
1. error indicator - 0 if there was no error, otherwise error number
2. the number of blocks
3. the number of free blocks
4. the number of blocks under writeback
Messages:
flush
flush the cache device. The message returns successfully
if the cache device was flushed without an error
flush_on_suspend
flush the cache device on next suspend. Use this message
when you are going to remove the cache device. The proper
sequence for removing the cache device is:
1. send the "flush_on_suspend" message
2. load an inactive table with a linear target that maps
to the underlying device
3. suspend the device
4. ask for status and verify that there are no errors
5. resume the device, so that it will use the linear
target
6. the cache device is now inactive and it can be deleted
......@@ -334,6 +334,17 @@ config DM_CACHE_SMQ
of less memory utilization, improved performance and increased
adaptability in the face of changing workloads.
config DM_WRITECACHE
tristate "Writecache target"
depends on BLK_DEV_DM
---help---
The writecache target caches writes on persistent memory or SSD.
It is intended for databases or other programs that need extremely
low commit latency.
The writecache target doesn't cache reads because reads are supposed
to be cached in standard RAM.
config DM_ERA
tristate "Era target (EXPERIMENTAL)"
depends on BLK_DEV_DM
......
......@@ -67,6 +67,7 @@ obj-$(CONFIG_DM_ERA) += dm-era.o
obj-$(CONFIG_DM_LOG_WRITES) += dm-log-writes.o
obj-$(CONFIG_DM_INTEGRITY) += dm-integrity.o
obj-$(CONFIG_DM_ZONED) += dm-zoned.o
obj-$(CONFIG_DM_WRITECACHE) += dm-writecache.o
ifeq ($(CONFIG_DM_UEVENT),y)
dm-mod-objs += dm-uevent.o
......
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