Date: Thu, 05 Nov 2015 10:56:55 -0800 From: Kirk McKusick <mckusick@mckusick.com> To: Konstantin Belousov <kostikbel@gmail.com> Cc: Bruce Evans <brde@optusnet.com.au>, fs@freebsd.org Subject: Re: an easy (?) question on namecache sizing Message-ID: <201511051856.tA5Iutge064958@chez.mckusick.com> In-Reply-To: <20151103090448.GC2257@kib.kiev.ua>
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> Date: Tue, 3 Nov 2015 11:04:48 +0200
> From: Konstantin Belousov <kostikbel@gmail.com>
> To: Kirk McKusick <mckusick@mckusick.com>
> Subject: Re: an easy (?) question on namecache sizing
>
> Free vnodes could be freed in the soft fashion by vnlru daemon, or in
> hard manner, by the getnewvnode(), when the max for the vnode count is
> reached. The 'soft' way skips vnodes which are directories, to make it
> more probable that vn_fullpath() would succeed, and also has threshold
> for the count of cached pages. The 'hard' way waits up to 1 sec for
> the vnlru daemon to succeed, before forcing a recycle for any vnode,
> regardless of the 'soft' stoppers. This causes the ticking behaviour of
> the system when only one vnode operation in single thread succeeds in a
> second.
>
> Large wantfreevnodes value is the safety measure to prevent the tick
> steps in practice. My initial reaction on the complain was to just
> suggest to increase desiredvnodes, at least this is what I do on
> machines where there is a lot of both KVA and memory and intensive file
> loads are expected.
I propose that we update wantfreevnodes in sysctl_update_desiredvnodes()
so that it tracks the change in desiredvnodes:
Index: /sys/kern/vfs_subr.c
===================================================================
--- /sys/kern/vfs_subr.c (revision 290387)
+++ /sys/kern/vfs_subr.c (working copy)
@@ -293,6 +293,7 @@
if (old_desiredvnodes != desiredvnodes) {
vfs_hash_changesize(desiredvnodes);
cache_changesize(desiredvnodes);
+ wantfreevnodes = desiredvnodes / 4;
}
return (0);
}
Otherwise bumping up desiredvnodes will be less effective than expected.
I see that Bruce has also suggested this change in his more extensive
revisions.
Kirk McKusick
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