[squid-dev] [PATCH] shared_memory_locking

[Alex Rousskov]

Hello,

    The attached patch adds a "shared_memory_locking" configuration
directive to control mlock(2).

Locking shared memory at startup avoids SIGBUS crashes when kernel runs
out of RAM during runtime. This has been discussed during the "[RFC] Fix
shared memory initialization, cleanup. Ensure its usability." thread
archived at
http://lists.squid-cache.org/pipermail/squid-dev/2015-December/004112.html

Why not enable locking by default? Unfortunately, locking requires
privileges and/or much-higher-than-default RLIMIT_MEMLOCK limits. Thus,
requiring locked memory by default is likely to cause too many
complaints, especially since Squid has not required that before. Even
"make check" will not work in most environments (without making our unit
tests even less representative)! Thus, the default is off, at least for now.

As we gain more experience, we may enable locking by default while
making default locking failures non-fatal and warning about significant
[accumulated] locking delays. The proposed code was written to make
those possible future changes easier, but I am not volunteering to
implement them at this time.


Thank you,

Alex.
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