On Oct 20, 2012, at 1:02 PM, Andriy Gapon <a...@freebsd.org> wrote: > Author: avg > Date: Sat Oct 20 10:02:18 2012 > New Revision: 241773 > URL: http://svn.freebsd.org/changeset/base/241773 > > Log: > zfs: wait in arc_lowmem only if curproc == pageproc > > ... otherwise the current thread might be holding ARC locks and thus run > into a deadlock. This happens, for example, when a thread does memory > allocation in the ARC code and runs into KVA shortage. > Also, it really makes the most sense to wait in pageproc, so that the > results of ARC reclamation are seen before the page cache is acted upon. > In other cases where vm_lowmem is invoked, e.g. on KVA space shortage, > the callers perform multiple attempts (up to 8) and wait for rather > long intervals between them (up to 4 seconds), so ARC reclaim results > should become visible even without explicit waiting on the ARC thread. > > Note that this is not a critical issue for typical ZFS usages where KVA > space should already be large enough. On amd64 systems setting KVA size > to twice the physical memory size is known to mitigate KVA fragmentation > issues in practice. > > Side note: perhaps vm_lowmem 'how' parameter should be used to > differentiate between causes of the event. > > Reported by: Nikolay Denev <nde...@gmail.com> > MFC after: 19 days > > Modified: > head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/arc.c
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