dirhash and dynamic memory allocation

[b. f.]

Miroslav Lachman wrote:
> Jeremy Chadwick wrote:
> > On Fri, Oct 14, 2011 at 02:33:18PM +0200, Miroslav Lachman wrote:
> >> Ivan Voras wrote:
> >>> On 14/10/2011 11:20, Miroslav Lachman wrote:
...
> >>>> I tried some tuning of dirhash on our servers and after googlig a bit, I
> >>>> found an old GSoC project wiki page about Dynamic Memory Allocation for
> >>>> Dirhash: http://wiki.freebsd.org/DirhashDynamicMemory
> >>>> Is there any reason not to use it / not commit it to HEAD?
...
> >> Is this change documented somewhere? Maybe it could be noticed on
> >> DirhashDynamicMemory wiki page. Otherwise it seems as abandoned GSoC
> >> project.
> >
> > There is no real form of "documentation" for this kind of change, but I
> > do remember it being discussed on the mailing list at some point (an
> > announcement or something?  I forget -- man it was a while ago).
>
> I didn't mean real doc (man page or handbook), but just some official
> place (release notes?) stating the change of the dirhash behavior.

>From the page you cited:

"Get code in a state suitable for being committed to -CURRENT. Done
...
(2009-7-7) I committed the dirhash vm_lowmem handler to -CURRENT about
a month ago, and it will be included in 8.0-RELEASE. Also I plan to
commit a backport of these changes to 7-STABLE, probably around
September."

>From http://www.FreeBSD.org/releases/7.3R/relnotes-detailed.html :

"UFS_DIRHASH (enabled by default) now supports removing the cache data
when the system memory is low (via vm_lowmem event handler). A bug
that the system caused a panic when decreasing a sysctl variable
vfs.ufs.dirhash_maxmem below the current amount of memory used by
UFS_DIRHASH, has been fixed."

In the commit logs:

http://svnweb.FreeBSD.org/base/head/sys/ufs/ufs/ufs_dirhash.c?view=log

So the changes have been documented.  Perhaps not in exhaustive
detail, but enough to provide a basis for further inquiry.  And as
someone pointed out, there are the suggestively-named OIDs, and their
descriptions.

b.