From 69be1a222ae173e5cdd5c3cc47eab78e65299c72 Mon Sep 17 00:00:00 2001 From: Joel Sherrill Date: Tue, 20 Oct 2015 14:47:10 -0500 Subject: CONFIGURE_IMFS_MEMFILE_BYTES_PER_BLOCK was undocumented and not error checked closes #2431. --- doc/user/conf.t | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 55 insertions(+) (limited to 'doc/user/conf.t') diff --git a/doc/user/conf.t b/doc/user/conf.t index ec9b1f8172..0dd0a50924 100644 --- a/doc/user/conf.t +++ b/doc/user/conf.t @@ -2748,6 +2748,61 @@ options will be defined as well @item @code{CONFIGURE_IMFS_DISABLE_UNMOUNT}. @end itemize +@c +@c === CONFIGURE_IMFS_MEMFILE_BYTES_PER_BLOCK === +@c +@subsection Specify Block Size for IMFS + +@findex CONFIGURE_IMFS_MEMFILE_BYTES_PER_BLOCK + +@table @b +@item CONSTANT: +@code{CONFIGURE_IMFS_MEMFILE_BYTES_PER_BLOCK} + +@item DATA TYPE: +Boolean feature macro. + +@item RANGE: +Valid values for this configuration parameter are a power of two (2) +between 16 and 512 inclusive. In other words, valid values are 16, +32, 64, 128, 256,and 512. + +@item DEFAULT VALUE: +The default IMFS block size is 128 bytes. + +@end table + +@subheading DESCRIPTION: +This configuration parameter specifies the block size for in-memory files +managed by the IMFS. The configured block size has two impacts. The first +is the average amount of unused memory in the last block of each file. For +example, when the block size is 512, on average one-half of the last block +of each file will remain unused and the memory is wasted. In contrast, +when the block size is 16, the average unused memory per file is only +8 bytes. However, it requires more allocations for the same size file +and thus more overhead per block for the dynamic memory management. + +Second, the block size has an impact on the maximum size file that can +be stored in the IMFS. With smaller block size, the maximum file size +is correspondingly smaller. The following shows the maximum file size +possible based on the configured block size: + +@itemize @bullet +@item when the block size is 16 bytes, the maximum file size is 1,328 +bytes. +@item when the block size is 32 bytes, the maximum file size is 18,656 +bytes. +@item when the block size is 64 bytes, the maximum file size is 279,488 +bytes. +@item when the block size is 128 bytes, the maximum file size is +4,329,344 bytes. +@item when the block size is 256 bytes, the maximum file size is +68,173,568 bytes. +@item when the block size is 512 bytes, the maximum file size is +1,082,195,456 bytes. +@end itemize + + @c @c === CONFIGURE_IMFS_DISABLE_CHOWN === @c -- cgit v1.2.3