doc: clarify what --alloc-size does

[fio.git] / HOWTO

diff --git a/HOWTO b/HOWTO
index 1c9b2c1020f7e7d53b43926fcb3c3369a1db07f8..4fef1504a410a205c95c7c85b489f0068bceb1a5 100644 (file)
--- a/HOWTO
+++ b/HOWTO
@@ -222,8 +222,8 @@ Command line options
 
 .. option:: --alloc-size=kb
 
-       Set the internal smalloc pool size to `kb` in KiB.  The
-       ``--alloc-size`` switch allows one to use a larger pool size for smalloc.
+       Allocate additional internal smalloc pools of size `kb` in KiB.  The
+       ``--alloc-size`` option increases shared memory set aside for use by fio.
        If running large jobs with randommap enabled, fio can run out of memory.
        Smalloc is an internal allocator for shared structures from a fixed size
        memory pool and can grow to 16 pools. The pool size defaults to 16MiB.
@@ -1252,7 +1252,9 @@ I/O type
        is incremented for each sub-job (i.e. when :option:`numjobs` option is
        specified). This option is useful if there are several jobs which are
        intended to operate on a file in parallel disjoint segments, with even
-       spacing between the starting points.
+       spacing between the starting points. Percentages can be used for this option.
+       If a percentage is given, the generated offset will be aligned to the minimum
+       ``blocksize`` or to the value of ``offset_align`` if provided.
 
 .. option:: number_ios=int
 
@@ -2031,6 +2033,12 @@ with the caveat that when used on the command line, they must come after the
        map and release for each IO. This is more efficient, and reduces the
        IO latency as well.
 
+.. option:: registerfiles : [io_uring]
+       With this option, fio registers the set of files being used with the
+       kernel. This avoids the overhead of managing file counts in the kernel,
+       making the submission and completion part more lightweight. Required
+       for the below :option:`sqthread_poll` option.
+
 .. option:: sqthread_poll : [io_uring]
 
        Normally fio will submit IO by issuing a system call to notify the