CVS commit: [tls-maxphys] src/sys/ufs/ufs

["Thor Lancelot Simon" <tls%netbsd.org@localhost>]

Module Name:    src
Committed By:   tls
Date:           Sun Oct 14 14:33:32 UTC 2012

Modified Files:
        src/sys/ufs/ufs [tls-maxphys]: ufs_readwrite.c

Log Message:
In the FFS writebehind code (ufs_readwrite.c:WRITE()), use division
and multiplication instead of shifts, to accomodate devices with
MAXPHYS that is a multiple of the page size, but not a power of 2.

MegaRAID neatly writes out 192k chunks now.

An open question: is is really a good idea to always writebehind
at the largest size supported by the device?  Likely not, as this
could have a major impact on I/O fairness.  OS X and Solaris both
seem to limit transfers to 128k likely for this reason (the same
problem exists with the readahead code but since it is adaptive,
it will not *always* do huge transfers).

However, simply imposing a smallish limit like 128k here seems
like a bad idea because then we cannot accomodate greedy devices
like RAID, for which you want something like 128k * number of
data components.  Hmmmmmm.


To generate a diff of this commit:
cvs rdiff -u -r1.104 -r1.104.2.1 src/sys/ufs/ufs/ufs_readwrite.c

Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.