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On Red Hat Linux 7.x, the default limit on ptys is set to 2048 for i686 and athlon kernels. Standard i386 and similar kernels default to 256 ptys.<br>
<br>
The config directive CONFIG_UNIX98_PTY_COUNT defaults to 256, but can be set as high as 2048. For 2048 ptys to be supported, the value of UNIX98_PTY_MAJOR_COUNT needs to be set to 8 in include/linux/major.h<br>
<br>
With the current device number scheme and allocations, the maximum number of ptys is 2048.<br>
<br>
Increasing Thread Limits<br>
Limitations on threads are tightly tied to both file descriptor limits, and process limits.<br>
Under Linux, threads are counted as processes, so any limits to the number of processes also applies to threads. In a heavily threaded app like a threaded TCP engine, or a java server, you can quickly run out of threads.<br>
<br>
The first step to increasing the possible number of threads is to make sure you have boosted any process limits as mentioned before.<br>
<br>
There are few things that can limit the number of threads, including process limits, memory limits, mutex/semaphore/shm/ipc limits, and compiled in thread limits. For most cases, the process limit is the first one to run into, then the compiled in thread limits, then the memory limits.<br>
<br>
To increase the limits, you have to recompile glibc. Oh fun!. And the patch is essentially two lines!. Woohoo!<br>
<br>
<br>
--- ./linuxthreads/sysdeps/unix/sysv/linux/bits/local_lim.h.akl Mon Sep 4<br>
19:37:42 2000<br>
+++ ./linuxthreads/sysdeps/unix/sysv/linux/bits/local_lim.h Mon Sep 4<br>
19:37:56 2000<br>
@@ -64,7 +64,7 @@<br>
/* The number of threads per process. */<br>
#define _POSIX_THREAD_THREADS_MAX 64<br>
/* This is the value this implementation supports. */<br>
-#define PTHREAD_THREADS_MAX 1024<br>
+#define PTHREAD_THREADS_MAX 8192<br>
<br>
/* Maximum amount by which a process can descrease its asynchronous I/O<br>
priority level. */<br>
--- ./linuxthreads/internals.h.akl Mon Sep 4 19:36:58 2000<br>
+++ ./linuxthreads/internals.h Mon Sep 4 19:37:23 2000<br>
@@ -330,7 +330,7 @@<br>
THREAD_SELF implementation is used, this must be a power of two and<br>
a multiple of PAGE_SIZE. */<br>
#ifndef STACK_SIZE<br>
-#define STACK_SIZE (2 * 1024 * 1024)<br>
+#define STACK_SIZE (64 * PAGE_SIZE)<br>
#endif<br>
<br>
/* The initial size of the thread stack. Must be a multiple of PAGE_SIZE.<br>
* */<br>
Now just patch glibc, rebuild, and install it. ;-&gt; If you have a package based system, I seriously suggest making a new package and using it.<br>
Two references on how to do this are Jlinux.org, and Volano.Both describe how to increase the number of threads so Java apps can use them.<br>
<br>
Increasing ulimits or shell limits<br>
OK, so this isn't kernel tuning but it may be as issue that you have to deal with, here is how you set the shell security limits up for you application:<br>
"In bash and similar shells you can use these three<br>
commands:<br>
ulimit -a<br>
ulimit -Ha<br>
ulimit -s unlimited<br>
that will respectively print soft limits, hard limits<br>
and remove the stack limit."<br>
<br>
The source for this information came from this Usenet article.<br>
<br>
Large File Support<br>
Large file support - support for files greater than 2 GB - is a kernel AND user space issue, meaning that not just the kernel has to be able to support file larger than 2 GB but also the C library (libc or for GUN/Linux glibc) and all file accessing utilities have to support it as well. See the LFS section in the links page for links with detailed information.<br>
<br>
<br>
Improving System Performance<br>
<br>
Tuning (delaying) filesystem cache synchronization (flushing)<br>
Increasing the time between when the kernel writes will minimize the amount of I/O done at the cost of losing more data if the system were to crash. See the following link from the linuxdoc.org site from the Securing and Optimizing Red Hat Linux Edition.<br>
<br>
Tuning virtual memory system to use less memory on servers with *lots* of memory on 2.0.x or 2.2.x (from Tani Hosokawa)<br>
Memory shortages (even though you've got tons) - for Linux 2.0.x/2.2.x<br>
Sometimes, you'll end up with a situation where the kernel can't seem to find<br>
enough memory to load a program for you, even though you've got tons of<br>
memory. This may be caused by the filesystem buffers using up the extra, and<br>
not having enough memory immediately available. You can often fix this by<br>
modifying the contents of /proc/sys/vm/freepages (the three values are<br>
min_free_pages, free_pages_low, and free_pages_high in case you care -- check<br>
the source for more details). "256 512 768" is common, but often not enough.<br>
I use "1024 2048 3072" usually. That's almost definitely enough memory to load<br>
anything, and with 384 megs of RAM, it's not going to hurt performance by<br>
reducing the amount available for caching.<br>
<br>
<br>
呵呵,看了一上午,感谢弱智兄,关于linux optimizing 的好文章<br>
<br>
补充:<br>
<br>
Securing and Optimizing Linux: RedHat Edition -A Hands on Guide<br>
Prev Chapter 6. Linux General Optimization Next<br>
<br>
--------------------------------------------------------------------------------<br>
<br>
6.5. The bdflush parameters<br>
The bdflush file is closely related to the operation of the virtual memory VM subsystem of the Linux kernel and has a little influence on disk usage. This file /proc/sys/vm/bdflush controls the operation of the bdflush kernel daemon. We generally tune this file to improve file system performance. By changing some values from the default as shown below, the system seems more responsive; e.g. it waits a little more to write to disk and thus avoids some disk access contention.<br>
<br>
The default setup for the bdflush parameters under Red Hat Linux is: "40 500 64 256 500 3000 500 1884 2" To change the values of bdflush, type the following command on your terminal:<br>
<br>
<br>
<br>
[root@deep] /# echo "100 1200 128 512 15 5000 500 1884 2"&gt;/proc/sys/vm/bdflush<br>
<br>
<br>
You may add the above commands to the /etc/rc.d/rc.local script file and you'll not have to type it again the next time you reboot your system.<br>
<br>
<br>
<br>
<br>
Edit the /etc/sysctl.conf file and add the following line: # Improve file system performance<br>
vm.bdflush = 100 1200 128 512 15 5000 500 1884 2<br>
<br>
<br>
You must restart your network for the change to take effect. The command to manually restart the network is the following: [root@deep] /# /etc/rc.d/init.d/network restart<br>
<br>
<br>
<br>
Setting network parameters [ OK ] Bringing up interface lo [ OK ] Bringing up interface eth0 [ OK ] Bringing up interface eth1 [ OK ]<br>
<br>
<br>
In our example above, according to the/usr/src/linux/Documentation/sysctl/vm.txt file-<br>
<br>
The first parameter 100 %<br>
governs the maximum number of dirty buffers in the buffer cache. Dirty means that the contents of the buffer still have to be written to disk as opposed to a clean buffer, which can just be forgotten about. Setting this to a high value means that Linux can delay disk writes for a long time, but it also means that it will have to do a lot of I/O at once when memory becomes short. A low value will spread out disk I/O more evenly.<br>
<br>
The second parameter 1200 ndirty<br>
This gives the maximum number of dirty buffers that bdflush can write to the disk in one time. A high value will mean delayed, bursty I/O, while a small value can lead to memory shortage when bdflush isn't woken up often enough.<br>
<br>
The third parameter 128 nrefill<br>
This is the number of buffers that bdflush will add to the list of free buffers when refill_freelist() is called. It is necessary to allocate free buffers beforehand, since the buffers often are of a different size than memory pages and some bookkeeping needs to be done beforehand. The higher the number, the more memory will be wasted and the less often refill_freelist() will need to run.<br>
<br>
refill_freelist() 512<br>
When this comes across more than nref_dirt dirty buffers, it will wake up bdflush.<br>
<br>
age_buffer 50*HZ, age_super parameters 5*HZ<br>
Finally, the age_buffer 50*HZ and age_super parameters 5*HZ govern the maximum time Linux waits before writing out a dirty buffer to disk. The value is expressed in jiffies (clockticks); the number of jiffies per second is 100. Age_buffer is the maximum age for data blocks, while age_super is for file system metadata.<br>
<br>
The fifth 15 and the last two parameters 1884 and 2<br>
These are unused by the system so we don't need to change the default ones.<br>
<br>
<br>
: Look at /usr/src/linux/Documentation/sysctl/vm.txt for more information on how to improve kernel parameters related to virtual memory.
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