https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=248008
Mark Johnston <[email protected]> changed: What |Removed |Added ---------------------------------------------------------------------------- CC| |[email protected] --- Comment #5 from Mark Johnston <[email protected]> --- I think the suggested patch is ok, but not for the reason stated. On platforms without a direct map the problem is: to allocate btags we need a slab, and to allocate a slab we need to map a page, and to map a page we need to allocate btags. We handle this recursion using a custom slab allocator which specifies M_USE_RESERVE, allowing it to dip into a reserve of free btags. Because the returned slab can be used to keep the reserve populated, this ensures that there are always enough free btags available to handle the recursion. UMA_ZONE_NOFREE ensures that we never reclaim free slabs from the zone. However, when it was removed, an apparent bug in UMA was exposed: keg_drain() ignores the reservation set by uma_zone_reserve() in vmem_startup(). So under memory pressure we reclaim the free btags that are needed to break the recursion. That's why adding _NOFREE back fixes the problem: it disables the reclamation. We could perhaps fix it more cleverly, by modifying keg_drain() to always leave uk_reserve slabs available. -- You are receiving this mail because: You are the assignee for the bug. _______________________________________________ [email protected] mailing list https://lists.freebsd.org/mailman/listinfo/freebsd-bugs To unsubscribe, send any mail to "[email protected]"
