Red Hat ENTERPRISE 5.4 RELEASE NOTES, Manual

Page: 144 / 466

Chapter 1. Package Updates
126
• Pointer and signed arithmetic overflow wrapping has not previously been defined in the Linux kernel.
This could cause
GCC
(GNU C Compiler) to assume that wrapping does not occur and attempt
to optimize the arithmetic that the kernel may require for overflow testing. This update adds the
-
fwrapv
variable to
GCC
CFLAGS
in order to define wrapping behavior.(
BZ#491266
876
)
• An issue of contention between processes vying for the same memory space in high end
systems was recently identified by TPC-C (Transaction Processing Council) benchmarking. This
update includes
fast-gup
patches which use direct IO and provide a significant (up to 9-10%)
performance improvement. This update has been tested thoroughly and is used in the 5.4 kernel to
improve scalability. For further information, see this
article
877
. (
BZ#474913
878
)
• A new parameter has been added to this kernel, allowing system administrators to change the
maximum number of modified pages
kupdate
writes to disk per iteration each time it runs.
/proc/
sys/vm/max_writeback_pages
defaults to
1024
or 4MB so that a maximum of 1024 pages get
written out by each iteration of
kupdate
. (
BZ#479079
879
).
• A new option (
CONFIG_TASK_IO_ACCOUNTING=y
) has been added to kernel to assist in
monitoring IO statistics per process. This assists with troubleshooting in a production environment.
(
BZ#461636
880
)
• In previous kernels, back-up processes were deteriorating
DB2
server responsiveness. This was
caused by
/proc/sys/vm/dirty_ratio
preventing processes writing to pagecache memory
when more than half of the unmapped pagecache memory was dirty (even if
dirty_ratio
was
set to 100%). A change made in this kernel update overrides this limiting behavior. Now, when
the
dirty_ratio
is set to 100%, the system will no longer limit writing to pagecache memory.
(
BZ#295291
881
)
• The
rd_blocksize
option found in the previous kernel's ramdisk driver was causing data
corruption when using large ramdisks under a reasonable system load. This update removes this
unnecessary option and resolves the data corruption issues. (
BZ#480663
882
)
• The function
getrusage
is used to examine the resource usage of a process. It is useful in
diagnosing problems and gathering data on resource usage. However, in instances where a process
was spawning child threads,
getrusage
's results would be in incorrect as it would examine only
the parent process and not interrogate its children. This update implements
rusadge_thread
to
allow for accurate resource usage results in these instances. (
BZ#451063
883
)
• The header
/usr/include/linux/futex.h
would previously interfere with compiling C source
code files, resulting in an error. This update includes a patch which corrects problematic kernel only
definitions and resolves the compiling error. (
BZ#475790
884
)
• In previous kernels the kernel version was not identified in
panic
or
oops
output messages. This
update adds the kernel version details to these outputs. (
BZ#484403
885
)
• During release 2.6.18, the kernel was configured to provide kernel-headers for the package
glibc
.
That process caused various files to be improperly marked for inclusion. The
serial_reg.h
file was incorrectly marked and not included in the
kernel_headers
rpm. This, in turn, caused
problems with building other rpms. This update adds the
serial_reg.h
file and corrects the
problem. (
BZ#463538
886
)
• In some circumstances
upcrund
, the process manager in HP's
Unified Parallel C
(UPC) product,
returned an ESRCH result and failed when calling
setpgid()
for a child process forked by a sub-
thread. This update includes a patch to fix for this problem. (
BZ#472433
887
)