[RFC PATCH v2 00/11] Add (de)compression support to pstore

Aruna Balakrishnaiah aruna at linux.vnet.ibm.com
Fri Aug 16 23:17:21 EST 2013

Changes from v1:
	- Allocate compression workspace during initialisation as
	per Tony's suggestion
         - Copy the recent messages from big_oops_buf to psinfo->buf
	when compression fails, since the printk buffer
        would be fetched for compression calling it again when
        compression fails would have moved the iterator of
        printk buffer which results in fetching old contents.

The patchset adds compression and decompression support to pstore.

As the non-volatile storage space is limited, adding compression
support results in capturing more data within limited space.

Size of dmesg file in a powerpc/pseries box with nvram's
oops partition (to store oops-log) size 4k:

Without compression:
dmesg-nvram-1:  ~ 4k (3980)
WIth compression:
dmesg-nvram-1: ~8.8k (8844)

Writing to persistent store
Compression will reduce the size of oops/panic report to atmost 45% of its
original size. (Based on experiments done while providing compression support
to nvram by Jim keniston).
Hence buffer of size ( (100/45 approx 2.22) *<registered_buffer> is allocated). 
The compression parameters selected based on some experiments:
compression_level = 6, window_bits = 12, memory_level = 4  achieved a
significant compression.
Data is compressed from the bigger buffer to registered buffer which is
returned to backends.
Pstore will indicate that with a flag 'compressed' which is passed to backends.
Using this flag, backends will add a flag in their header to indicate the data
is compressed or not while writing to persistent store.

Reading from persistent store
When backends read data from persistent store it will use the flag added by it
while writing to persistent store to determine if the data is compressed or not.
Using the information, it will set the flag in pstore's read call back.
Pstore will decompress the data based on the flag and writes decompressed data
to the file.

Test results:
Have tested the patches on powerpc/pseries.

Needs testing with erst backend, efivars and persistent ram.


Aruna Balakrishnaiah (11):
      powerpc/pseries: Remove (de)compression in nvram with pstore enabled
      pstore: Add new argument 'compressed' in pstore write callback
      pstore/Kconfig: Select ZLIB_DEFLATE and ZLIB_INFLATE when PSTORE is selected
      pstore: Add compression support to pstore
      pstore: Introduce new argument 'compressed' in the read callback
      pstore: Add decompression support to pstore
      pstore: Add file extension to pstore file if compressed
      powerpc/pseries: Read and write to the 'compressed' flag of pstore
      erst: Read and write to the 'compressed' flag of pstore
      efi-pstore: Read and write to the 'compressed' flag of pstore
      pstore/ram: Read and write to the 'compressed' flag of pstore

 arch/powerpc/platforms/pseries/nvram.c |  112 +++--------------
 drivers/acpi/apei/erst.c               |   21 ++-
 drivers/firmware/efi/efi-pstore.c      |   27 +++-
 fs/pstore/Kconfig                      |    2 
 fs/pstore/inode.c                      |    7 +
 fs/pstore/internal.h                   |    5 -
 fs/pstore/platform.c                   |  212 ++++++++++++++++++++++++++++++--
 fs/pstore/ram.c                        |   41 +++++-
 include/linux/pstore.h                 |    6 -
 9 files changed, 299 insertions(+), 134 deletions(-)


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