09-18-2014
Quote:
Originally Posted by
achenle
In your case, I suspect the C++ core is probably mmap() anonymous memory, requesting large pages, and using them for video processing buffers. And, unfortunately, then releasing them, allowing the page cache to fragment the large pages. Eventually you get to the point where there are no large pages available because of fragmentation.
Would turning off hugepages somehow be a solution? It could be just one bit in a binary's code segment somewhere... There'd be a performance hit from using small pages but less than the hit of not getting the memory you need at all...
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LEARN ABOUT HPUX
pagezero_daemon_enabled
pagezero_daemon_enabled(5) File Formats Manual pagezero_daemon_enabled(5)
NAME
pagezero_daemon_enabled - zeroing of free memory in the background is enabled
VALUES
Default
Allowed values
Minimum:
Maximum:
DESCRIPTION
HP-UX provides improved security by zeroing out any memory that is being assigned to user space. This ensures that no user can read what
may have been written by some other user. Normally, the zeroing is done when the physical page is allocated to the user -- often when the
application touches the page for the first time. Some system calls like also result in the zeroing of pages. The time taken for these
kind of system calls and accesses depends upon the size of the memory being zeroed out. A 4G page may easily take many seconds to be allo-
cated. A large database shared memory segment may take many minutes to be allocated. Allocation of a small page is generally unobserv-
able.
The daemon is a performance enhancement that reduces the elapsed time for completing kernel operations like page faults, and so on. The
idea is to zero out large free pages (4MB and above in size) during times when the CPU is idle. The daemon has been specially designed to
ensure that it only executes for brief times when the CPU is idle.
However, under certain conditions, where some resource (CPU, TLB or Memory bandwidth) is very highly utilized, it is possible that the
operation of the daemon adversely impacts performance. For example, if the application is limited by the memory bandwidth, then it may be
better to disable the daemon. This situation is expected to be rare. Most workloads will not need to disable the daemon.
This tunable allows system administrators to disable and enable the daemon. Once the daemon has been disabled, it will not zero out any
more pages. Any pages already in the process of being zeroed will be zeroed out. When the daemon is enabled, it will zero out any unze-
roed free pages of size 4MB and more.
Who is Expected to Change This Tunable?
Anyone.
Restrictions on Changing
Changes to this tunable take effect immediately.
When Should the Value of This Tunable Be Changed to 0?
This tunable should be changed only if the system is using large pages (i.e. is set to 4MB or above). Changing it if the system is not
using pages of size 4M and above will have no effect. It may be changed to 0 if the system is bottle-necked on some hardware resource. In
particular, disabling the daemon may help in decreasing TLB misses and increasing the available CPU time and reducing memory latencies.
What Are the Side Effects of changing the value to 0?
Disabling the daemon will increase the time it takes to process page faults and to complete system calls that result in the allocation of
memory (e.g.
WARNINGS
All HP-UX kernel tunable parameters are release specific. This parameter may be removed or have its meaning changed in future releases of
HP-UX.
Installation of optional kernel software, from HP or other vendors, may cause changes to tunable parameter values. After installation,
some tunable parameters may no longer be at the default or recommended values. For information about the effects of installation on tun-
able values, consult the documentation for the kernel software being installed. For information about optional kernel software that was
factory installed on your system, see at
AUTHOR
was developed by HP.
SEE ALSO
vps_ceiling(5).
Tunable Kernel Parameters pagezero_daemon_enabled(5)