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Re: kern/54818: 9.0_RC1 pagedaemon spins

The following reply was made to PR kern/54818; it has been noted by GNATS.

From: (Michael van Elst)
Subject: Re: kern/54818: 9.0_RC1 pagedaemon spins
Date: Wed, 4 Mar 2020 12:09:53 -0000 (UTC) (Havard Eidnes) writes:
 > Does the number of files on this host perhaps impact this?
 The number of files touched determines how many vnodes and 
 associated data structures are cached. And that's in KVA.
 > vcachepl     336   844075    0        0 70340     0 70340 70340     0   inf    0
 The vnode cache acquired 70340 pages (about 844000 entries) and never
 released anything. That's not special for such a machine. But there
 is more data referenced by the cache that can only be evicted if the
 cache entry is removed. The real memory footprint can be much larger.
 It's possible that kern.maxvnodes is too large nowadays, but also
 important is that vnodes are not evicted under memory pressure.
 Maybe the page daemon should invoke vfs_drainvnodes(), even when it
 is not an issue here, I suspect maxvnodes to be larger than 844000.
 Then the page daemon must be able to shrink the cache below the
 maxvnodes value.
                                 Michael van Elst
                                 "A potential Snark may lurk in every tree."

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