This patch supports compression for bigger block size.
3 bits [57-59] in the COW Operation "source_info_" field is used to store
the compression factor. Supported compression factors are power of 2
viz: 4k, 8k, 16k, 32k, 64k, 128k, 256k.
Only REPLACE operations will have the bigger block size support for now.
This can be extended to other operations later.
The write path in EmitBlocks() has the core logic wherein consecutive
sequence of REPLACE ops are compressed based on the compression factor
settings. Thus, for a 64k compression factor, there will be just one
COW operation which encodes all the 16 operation and the entire 64k
block is compressed in one shot.
NOTE: There is no read I/O path support in this patch. Subsequent patch
will have the read support.
Performance data (with read I/O path support in subsequent patch):
go/variable-block-vabc-perf covers detail performance runs
on Pixel 6 for full and incremental OTA.
TL;DR:
Performance of a full OTA (All numbers are compared against 4k block
size)
=======================================
Snapshot-size:
~10-11% decrease in snapshot-size (disk-space) for zstd with 256k block
size.
~8% decrease in snapshot-size (disk-space) for lz4
Install time:
~13% decrease in OTA install time for zstd with 256k block size.
Snapshot-merge:
~50% decrease in snapshot-merge time with 256k block size for zstd
Post OTA boot-time:
~10.5 decrease in boot time for 64k block size for zstd
In-memory footprint for COW operations:
~80% decrease in memory footprint for 256k block size. (58MB -> 9.2MB)
============================================
For more improvements, further tuning of zstd/lz4 is
required primariy the compression levels, zstd compression window,
performance of gz with compression levels.
Bug: 319309466
Test: cow_api test covering all the supported block sizes for v3 writer.
On Pixel 6:
=======================================
COW Writer V3:
for OTA in full, incremental OTA
for block_size in 4k, 16k, 32k, 64k, 128k, 256k
for compression_algo in lz4, zstd, gz, none
install OTA, reboot, verify merge
=======================================
COW Writer V2:
for OTA in full, incremental OTA
for block_size in 4k
for compression_algo in lz4, zstd, gz, none
install OTA, reboot, verity merge
=====================================
Change-Id: I96201f1609582aa9d44d8085852e284b0c4a426d
Signed-off-by: Akilesh Kailash <akailash@google.com>
59fa486703