libnvdimm: Non-Volatile Devices

Maintainer information and documentation for drivers/nvdimm

Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Boaz Harrosh <boaz@plexistor.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jens Axboe <axboe@fb.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Neil Brown <neilb@suse.de>
Cc: Greg KH <gregkh@linuxfoundation.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

1 files changed, 17 insertions, 7 deletions

diff --git a/Documentation/nvdimm/btt.txt b/Documentation/nvdimm/btt.txt
index 95134d5ec4a0..b91443f577dc 100644
--- a/Documentation/nvdimm/btt.txt
+++ b/Documentation/nvdimm/btt.txt
@@ -80,9 +80,17 @@ block. Each map entry is 32 bits. The two most significant bits are special
 flags, and the remaining form the internal block number.
 
 Bit      Description
-31     : TRIM flag - marks if the block was trimmed or discarded
-30     : ERROR flag - marks an error block. Cleared on write.
-29 - 0 : Mappings to internal 'postmap' blocks
+31 - 30 : Error and Zero flags - Used in the following way:
+         Bit                  Description
+        31 30
+        -----------------------------------------------------------------------
+         00     Initial state. Reads return zeroes; Premap = Postmap
+         01     Zero state: Reads return zeroes
+         10     Error state: Reads fail; Writes clear 'E' bit
+         11     Normal Block – has valid postmap
+
+
+29 - 0  : Mappings to internal 'postmap' blocks
 
 
 Some of the terminology that will be subsequently used:
@@ -127,10 +135,11 @@ old_map': alternate old postmap entry
 new_map': alternate new postmap entry
 seq'    : alternate sequence number.
 
-Each of the above fields is 32-bit, making one entry 16 bytes. Flog updates are
+Each of the above fields is 32-bit, making one entry 32 bytes. Entries are also
+padded to 64 bytes to avoid cache line sharing or aliasing. Flog updates are
 done such that for any entry being written, it:
 a. overwrites the 'old' section in the entry based on sequence numbers
-b. writes the new entry such that the sequence number is written last.
+b. writes the 'new' section such that the sequence number is written last.
 
 
 c. The concept of lanes
@@ -141,8 +150,9 @@ concurrently, 'nlanes' is the number of IOs the BTT device as a whole can
 process.
  nlanes = min(nfree, num_cpus)
 A lane number is obtained at the start of any IO, and is used for indexing into
-all the on-disk and in-memory data structures for the duration of the IO. It is
-protected by a spinlock.
+all the on-disk and in-memory data structures for the duration of the IO. If
+there are more CPUs than the max number of available lanes, than lanes are
+protected by spinlocks.
 
 
 d. In-memory data structure: Read Tracking Table (RTT)