kernel bug fix update

Updated kernel packages that fix various bugs are now available for Red Hat
Enterprise Linux 4.5.

The kernel packages contain the Linux kernel, the core of any Linux
operating system.

These updated packages fix the following bugs:

* in directories mounted via NFS, pagecache data (cached information about
directories and their contents) was stored for too long. Applications
opening and reading files in these directories (eg the "tar" utility) would
read information from the cache and, when checking it against the fstat
(File Status) function, note the ctime had changed and throw an error. This
updated package discards pagecache data when the directories or their
contents are re-addressed, ensuring applications get accurate data about
mounted files from the NFS server.

* a client-side race on blocking locks caused large time delays for
operations on NFS file systems. In these situations, the "ps ax" command
displayed "blk_congestion_wait" messages for NFS processes.

* mapped memory was assumed to be in proportion to the highmem:lowmem
ratio. This turned out not to be the case and, on systems with a very large
highmem:lowmem ratio, this caused extremely poor NFS write performance when
writing small files. With this update you can set whether mapped file pages
are used in dirty_ratio and dirty_background_ratio calculations. To do so,
set /proc/sys/vm/write-mapped to 1 (this is set to 0 by default). Setting
/proc/sys/vm/write-mapped to 1 allows you to implement faster NFS read
performance. Note, however, that doing so exposes you to out-of-memory
risks.

Red Hat Enterprise Linux 4 users are advised to upgrade to these updated
packages, which contain backported patches to resolve these issues.

Before applying this update, make sure that all previously-released
errata relevant to your system have been applied.

This update is available via Red Hat Network. Details on how to use
the Red Hat Network to apply this update are available at
http://kbase.redhat.com/faq/FAQ_58_10188

437787 - NFS: Fix directory caching problem - with test case and patch.
438344 - [2.6.9-55.9] VM pagecache reclaim patch causes high latency on systems with large highmem/lowmem ratios
438476 - Since "Patch2037: linux-2.6.9-vm-balance.patch" my NFS performance is poorly
445181 - Granted file lock is processed in wrong thread on NFS client.

http://kbase.redhat.com/
http://kbase.redhat.com/faq/FAQ_42_11697.shtm