[v3,6/8] x86: bump ZO_z_extra_bytes margin for zstd
diff mbox series

Message ID 20200325195849.407900-7-nickrterrell@gmail.com
State New
Headers show
Series
  • Add support for ZSTD-compressed kernel and initramfs
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Commit Message

Nick Terrell March 25, 2020, 7:58 p.m. UTC
From: Nick Terrell <terrelln@fb.com>

Bump the ZO_z_extra_bytes margin for zstd.

Zstd needs 3 bytes per 128 KB, and has a 22 byte fixed overhead.
Zstd needs to maintain 128 KB of space at all times, since that is
the maximum block size. See the comments regarding in-place
decompression added in lib/decompress_unzstd.c for details.

Signed-off-by: Nick Terrell <terrelln@fb.com>
---
 arch/x86/boot/header.S | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

Patch
diff mbox series

diff --git a/arch/x86/boot/header.S b/arch/x86/boot/header.S
index 97d9b6d6c1af..b820875c5c95 100644
--- a/arch/x86/boot/header.S
+++ b/arch/x86/boot/header.S
@@ -536,8 +536,14 @@  pref_address:		.quad LOAD_PHYSICAL_ADDR	# preferred load addr
 # the size-dependent part now grows so fast.
 #
 # extra_bytes = (uncompressed_size >> 8) + 65536
+#
+# ZSTD compressed data grows by at most 3 bytes per 128K, and only has a 22
+# byte fixed overhead but has a maximum block size of 128K, so it needs a
+# larger margin.
+#
+# extra_bytes = (uncompressed_size >> 8) + 131072
 
-#define ZO_z_extra_bytes	((ZO_z_output_len >> 8) + 65536)
+#define ZO_z_extra_bytes	((ZO_z_output_len >> 8) + 131072)
 #if ZO_z_output_len > ZO_z_input_len
 # define ZO_z_extract_offset	(ZO_z_output_len + ZO_z_extra_bytes - \
 				 ZO_z_input_len)