Date: Sat, 20 Dec 2014 17:56:15 +0200 From: Konstantin Belousov <kostikbel@gmail.com> To: Stephen Mcconnell <stephen.mcconnell@avagotech.com> Cc: freebsd-scsi@freebsd.org Subject: Re: changing kern.bio_transient_maxcnt fixes panic Message-ID: <20141220155615.GT2148@kib.kiev.ua> In-Reply-To: <ceed8e57113129c0425c649b457afb89@mail.gmail.com> References: <ceed8e57113129c0425c649b457afb89@mail.gmail.com>
next in thread | previous in thread | raw e-mail | index | archive | help
On Fri, Dec 19, 2014 at 11:16:36AM -0700, Stephen Mcconnell wrote: > changing kern.bio_transient_maxcnt fixes panic > > Hi Konstantine. I hope you are the right person to help with this. Or > perhaps someone else on the list can help. > > We (Avago) have a customer who is getting the following panic. They are > using the mrsas (MegaRAID) driver in FreeBSD 10. In a test, they tried to > restore a database backup of 3GB. After the restore they queried the > database and then saw the panic. They found this link, saying that > changing the value of kern.bio_transient_maxcnt should fix the problem. It > did fix the problem, be we would like to know why it helped so that we???re > not just putting a band-aid on it. > > *https://lists.freebsd.org/pipermail/freebsd-stable/2013-October/075577.html* > <https://lists.freebsd.org/pipermail/freebsd-stable/2013-October/075577.html>; > > Also, I found this link with the same type of question. > > *https://docs.freebsd.org/cgi/getmsg.cgi?fetch=179246+182329+/usr/local/www/db/text/2014/freebsd-questions/20141019.freebsd-questions* > <https://docs.freebsd.org/cgi/getmsg.cgi?fetch=179246+182329+/usr/local/www/db/text/2014/freebsd-questions/20141019.freebsd-questions>; > > Can you explain why changing this value fixes this problem, and what we > might need to do in the driver to make a permanent fix? The tunable controls the size of the KVA area used to map pages of the bio's which are not mapped into KVA, but which are passed to a driver that requires mapped bio's. The auto-tuning logic was developed with an assumption that the system load consists of the typical UFS-generated I/O. It is possible, for some i/o pathes. to generate more i/o. Note that the transient mappings are only needed when the driver does not handle unmapped bio's. So the proper fix is to add support for the unmapped i/o, see e.g. mfi(4); the required modifications are relatively simple. If you driver already supports unmapped i/o, then there is something else going on.
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20141220155615.GT2148>