CVSROOT: /cvs
Module name: src
Changes by: [email protected] 2026/01/28 14:09:41
Modified files:
sys/uvm : uvm_pdaemon.c uvm_pmemrange.c uvm_pmemrange.h
Log message:
The pagedaemon inspects the top-most sleeping pmemrange allocation for
for size and constraint, and passes this information to the inactive
scanner. The idea is that an extremely high-size and
strict-constraint allocation that fails repeatedly would percolate to
the top of the list. To ensure the scanner can inspect this
allocation's constraint via the pointer, it gets locked. Then we
release tons of memory from the buffer cache, and run the scanner to
recover free memory. At the same time, other running operations free
and allocate memory and wakeup all the sleeping pmemrange allocations,
but no, not this one, because it is locked so that the pointer won't
become invalid. When the scan is done, we may once again have meager
memory resources because all the good stuff was allocated by
asyncronous allocators, potentially creating substantial fragmentation
not compatible with the constraint. Now, the sleeping request gets
unlocked and woken to re-check it's requirements and guess what, the
constraint fails it goes back to sleep, and we need to go around
again... In practice this is a hard uvm deadlock.
Instead, copy the constraint from the request, do not lock the
allocation request and ignore the pointer.
Instrumentation is showing this top-most request is ALWAYS satisfied
during the bufbackoff() sequence, but we'll continue passing the
constraint to the scanner as a last-ditch effort.
ok claudio beck kettenis
