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Subject[PATCH 1/2] fs/squashfs: Make SquashFS xz initialization mode configurable
Date
From: "yusun2@cisco.com" <yusun2@cisco.com>

Make SquashFS xz initialization mode configurable to be either
XZ_PREALLOC or XZ_DYNALLOC. The default mode is XZ_PREALLOC.

SquashFS multi-threaded per-CPU decompressor is proven to
effectively resolve the I/O bottleneck and boost the outcome
of other boot time optimization technologies on some I/O bound
platforms. However it allocates extra memory on per-processor
per-mounted-package basis. Making XZ_DYNALLOC mode an option
for the xz decompressor initialization in SquashFS minimizes
the memory impact.

Signed-off-by: Yu Sun <yusun2@cisco.com>
Cc: xe-linux-external@cisco.com
Signed-off-by: Daniel Walker <dwalker@fifo99.com>
---
fs/squashfs/Kconfig | 32 ++++++++++++++++++++++++++++++++
fs/squashfs/xz_wrapper.c | 6 +++++-
2 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/fs/squashfs/Kconfig b/fs/squashfs/Kconfig
index 916e78fabcaa..9cf2ebf89374 100644
--- a/fs/squashfs/Kconfig
+++ b/fs/squashfs/Kconfig
@@ -223,3 +223,35 @@ config SQUASHFS_FRAGMENT_CACHE_SIZE

Note there must be at least one cached fragment. Anything
much more than three will probably not make much difference.
+
+choice
+ prompt "XZ decompressor operation mode"
+ depends on SQUASHFS_XZ
+ default SQUASHFS_XZ_DICT_PREALLOC
+ help
+ Squashfs now utilizes the two different multi-call modes of xz
+ decompression. They each exhibits various trade-offs between
+ decompression performance and memory consumption.
+
+ If in doubt, select "XZ preallocated multi-call mode"
+
+config SQUASHFS_XZ_DICT_PREALLOC
+ bool "XZ preallocated multi-call mode"
+ help
+ Traditionally Squashfs has used XZ_PREALLOC operation mode for
+ xz decompression, under which the xz dictionary buffer is allocated
+ at initialization.
+
+config SQUASHFS_XZ_DICT_DYNALLOC
+ bool "XZ dynamic-allocated multi-call mode"
+ help
+ By default Squashfs uses XZ_PREALLOC operation mode for xz decompressor.
+ This, however, potentially lead to significant increase of memory
+ consumption, especially when SquashFS per-cpu multi-threaded
+ decompressor is applied.
+
+ If the system has memory constraints, setting this option will force
+ SquashFS to use XZ_DYNALLOC mode, and thus reduce memory footprint.
+ In this case, the LZMA2 dictionary is allocated upon needed with the
+ required size.
+endchoice
diff --git a/fs/squashfs/xz_wrapper.c b/fs/squashfs/xz_wrapper.c
index 4b2f2051a6dc..6d6946bb5e4c 100644
--- a/fs/squashfs/xz_wrapper.c
+++ b/fs/squashfs/xz_wrapper.c
@@ -90,7 +90,11 @@ static void *squashfs_xz_init(struct squashfs_sb_info *msblk, void *buff)
goto failed;
}

- stream->state = xz_dec_init(XZ_PREALLOC, comp_opts->dict_size);
+ if (IS_ENABLED(CONFIG_SQUASHFS_XZ_DICT_DYNALLOC)) {
+ stream->state = xz_dec_init(XZ_DYNALLOC, comp_opts->dict_size);
+ } else {
+ stream->state = xz_dec_init(XZ_PREALLOC, comp_opts->dict_size);
+ }
if (stream->state == NULL) {
kfree(stream);
err = -ENOMEM;
--
2.17.1
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