27.2 Tuning Cache Buffers for NSS

NSS manages cache buffers on Linux using methods similar to those used in other Linux file systems such as Reiser, Polyserve, and XFS, with the exception of EXT.

For file data, NSS uses the Linux cache page manager to gain access to available memory in the system. There are some limits in place so that when copying large files, NSS does not starve other user applications for memory. This is similar to the cache handling used in NetWare.

For metadata, NSS uses kernel memory. NSS can use only a percentage of this space because other applications share this space. By default, NSS reserves a minimum buffer cache size of 30,000 4-KB buffers, which is about 120 MB of the kernel memory space. You can adjust the minimum number of buffers to be used by NSS with the MinBufferCacheSize parameter.

The NSS Name Cache is responsible for caching the Name Tree information. This is the information that is read when you perform any kind of search by file or directory name. The Name Cache maps a name to a ZID (a unique file object ID). Directory listings do not do this as much as normal file opens that must resolve each name in the file path.

Use the NameCacheSize parameter to specify the amount of recently used Name Tree entries for files and directories that NSS caches. Each entry uses about 150 bytes of memory.

Increasing the maximum number of entries Name Cache entries does not necessarily improve the performance for getting directory listing information if NSS also needs to look up information about the file from a tree or structure outside of the name tree.

If you want to see how your name cache is performing, use the nsscon /NameCacheStats command.