Along with tune_t_flushr, autoup controls the amount of memory examined for dirty pages in each invocation and frequency of file system sync operations.
The value of autoup is also used to control whether a buffer is written out from the free list. Buffers marked with the B_DELWRI flag (file content pages that have changed) are written out whenever the buffer has been on the list for longer than autoup seconds. Increasing the value of autoup keeps the buffers around for a longer time in memory.
1 to MAXINT
If autoup is less than or equal to zero, it is reset to 30 and a warning message is displayed. This check is only done at boot time.
autoup should be an integer multiple of tune_t_fsflushr. At a minimum, autoup should be at least 6 times tune_t_fsflushr. If not, excessive amounts of memory will be scanned each time fsflush is invoked.
(total system pages x tune_t_fsflushr) should be greater than or equal to autoup to cause memory to be checked if dopageflush is non-zero.
There are several potential situations for changing autoup and or tune_t_fsflushr:
Systems with large amounts of memory—In this case, increasing autoup reduces the amount of memory scanned in each invocation of fsflush.
Systems with minimal memory demand—Increasing both autoup and tune_t_fsflushr reduces the number of scans made. autoup should be increased also to maintain the current ratio of autoup / tune_t_fsflushr.
Systems with large numbers of transient files (for example, mail servers or software build machines)—If large numbers of files are created and then deleted, fsflush might unnecessarily write data pages for those files to disk.