Date: Tue, 16 Oct 2001 20:36:26 -0700 (PDT) From: Matthew Dillon <dillon@apollo.backplane.com> To: hackers@FreeBSD.ORG Cc: Dag-Erling Smorgrav <des@ofug.org>, John Baldwin <jhb@FreeBSD.ORG>, Maxime Henrion <mux@qualys.com> Subject: First cut at kern.maxvnodes implementation Message-ID: <200110170336.f9H3aQI94211@apollo.backplane.com>
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Here is my first cut at implementing kern.maxvnodes. When playing with
the sysctl()s note that kern.minvnodes also exists and may have to be
messed around with.
http://apollo.backplane.com/FreeBSD4/
http://apollo.backplane.com/FreeBSD4/maxvnodes-01.diff
These patches are for -stable only. I'm going to get the code working
on -stable before I try to do a cut for -current.
There are notes up at the URL. Note that you cannot set maxvnodes
to an arbitrarily low number. Well, you can, but it won't be able
to meet the request because active vnodes (open files), buffer
cache references, and namei cache references (for directories containing
children) will prevent reuse. Thus, kern.maxvnodes is still a
soft-maximum, but if you set it (or leave it) at a reasonable value it
shouldn't exceed it by much.
Another very interesting effect of this patch is that in order to
enforce the requested kern.maxvnodes, we have to clear out vnodes that
may still have cached pages (i.e. its the presence of cached pages
that prevent the vnodes from being freed and cause the vnode count to
blow out the kernel malloc area). This means that it is actually
possible to stabilize physical memory use and still have a significant
number of truely-free pages.
The vast majority of systems never reach their programmed kern.maxvnodes,
they run out of physical memory first and so start recycling vnodes
that no longer have cached pages. Those that do have large-memory
configurations (2G+ typically) and are typically accessing a huge
number of small files. For example, a cvs mirror might have this
characteristic.
-Matt
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