Linux limits the low memory to less than 1GB on 32-bit machines, but places all physical memory in the low-memory area for 64-bit machines. By default, NSS on Linux caches its metadata blocks in the server's low memory. When the working set of metadata does not fit into low memory, performance is affected. In particular, metadata caching on servers with large numbers of files can create performance issues for servers that are low memory constrained as for 32-bit machines.
NSS for Linux supports metadata caching in high memory for servers that are low-memory constrained. This can greatly improve metadata reads on 32-bit systems with large numbers of files.
Enter the following command in the NSS Console (nsscon):
Set the type of use of User memory in 32-bit OES Linux as none, linux, or private. On 64-bit OES Linux, NSS does not use User memory at all.
Set up a separate user-mode cache in memory outside of the Linux cache. This is the default for 32-bit machines. By default, NSS takes 20 percent of the total high memory. You can modify this setting with the nss /PrivateCacheSizeInBlocks=value command.
However, If the number of Private Cache blocks is less than twice the NSS Cache blocks, then the default high memory cache type is linux. If the high memory is less than twice the NSS Cache blocks, then the default high memory cache type is none.
Private Cache is best used for dedicated file-servers. The Private Cache increases the performance of NSS, but reduces the amount of memory available to other file systems and tasks.
Integrate caching into the regular Linux caches. This is the default for 32-bit machines where the number of Private Cache blocks is less than twice the NSS Cache blocks.
This can be a problem on a dual purpose file-server and application-server system, because memory-hungry applications can cause the file-system cache to purge completely.
Use the same algorithm as the initial release of OES 1 Linux, which is to try and cache everything in Kernel-mode memory. This is the only option on 64-bit OES Linux. This is the default for 32-bit machines if the high memory is less than twice the NSS Cache blocks.
Sets the number of metadata blocks to cache for a 32-bit OES Linux machine where you have set the HighMemoryCacheType=private.
By default, NSS takes 20% of all high memory to use for the Private Cache. We recommend against giving NSS 100 percent of the high memory. The actual percentage you should allot depends on your deployment scenario. For example:
Which features of NSS are enabled--salvage, compression, and so on.
Use of really long filenames.
Use of extended attributes.
Default: 20 percent of all high memory blocks
Range: 0 blocks to the number of blocks available in high memory (total available high memory divided by 4KB)
To view the current settings for the high memory cash usage, enter
nss /status
View the following parameters in the Current NSS Status report:
The Current Private Cache Size indicates the amount of memory currently being used by the Private Cache. The Private Cache Size Limit shows the maximum amount of memory that the Private Cache can use. The High Memory Cache Type indicates the type of high memory cache that is being used as none, linux, or private.