Hello,
While working on the change proposal
https://fedoraproject.org/wiki/Changes/OptimizeSquashFS
I discovered that several kernel configuration options are set
sub-optimally in Fedora. In RHEL 8, the optimal configuration is used.
If we set those options to match RHEL 8, a performance improvement could
be achieved while reading the SquashFS filesystem.
Below you can see an excerpt from the configuration help:
Set in RHEL 8:
SQUASHFS_FILE_DIRECT
Directly decompress file data into the page cache.
Doing so can significantly improve performance because
it eliminates a memcpy and it also removes the lock contention
on the single buffer.
SQUASHFS_DECOMP_MULTI_PERCPU
By default Squashfs uses a single decompressor but it gives
poor performance on parallel I/O workloads when using multiple CPU
machines due to waiting on decompressor availability.
This decompressor implementation uses a maximum of one
decompressor per core. It uses percpu variables to ensure
decompression is load-balanced across the cores.
Set in Fedora:
SQUASHFS_DECOMP_SINGLE
Traditionally Squashfs has used single-threaded decompression.
Only one block (data or metadata) can be decompressed at any
one time. This limits CPU and memory usage to a minimum.
SQUASHFS_FILE_CACHE
Decompress file data into an intermediate buffer and then
memcopy it into the page cache.
The SquashFS filesystem is used on installation medium. So making the
change I propose should improve the user experience during installation.
It should also improve the user experience while booting from Fedora
Live image.
Kind regards,
--
Bohdan Khomutskyi
Software engineer
Red Hat
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