On Thu, Mar 18, 2021 at 01:36:55AM -0000, SaveTheRbtz wrote:
> Is it possible (pun intended) to compromise on
> `CONFIG_SQUASHFS_DECOMP_MULTI` (which uses num_online_cpus) instead of
> `CONFIG_SQUASHFS_DECOMP_MULTI_PERCPU` (which uses `num_possible_cpus`)?

It's better, but still not that great of a compromise in my opinion.
It's fine for systems with small numbers of CPUs. I still don't think it
scales well for large CPU systems. For instance, one machine I have
access to has 208 online cores. There we would have 26M of RAM allocated
just for the decompression caches for each squashfs mount, which
probably isn't fatal since large-cpu systems likely also have large
amounts of RAM, but it's also pretty wasteful since it's highly unlikely
that 208 squashfs decompressions for the same super block will be going
in parallel.

It's possible to convince us to change to that option, but we'd at least
need more information about what problems the current setting is causing
and some testing to confirm that changing the option helps. Please file
a new bug for this request. You can subscribe me to the bug.

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https://bugs.launchpad.net/bugs/1636847

Title:
  unexpectedly large memory usage of mounted snaps

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