[PATCH] Document how to setup/use huge pages

[fio.git] / HOWTO

diff --git a/HOWTO b/HOWTO
index 1e1f4097f54218e8c9d70e9479aecc9bf62c635d..996da23a1ce998665d1f9af7d65faaf064eced64 100644 (file)
--- a/HOWTO
+++ b/HOWTO
@@ -224,7 +224,9 @@ bs=siint    The block size used for the io units. Defaults to 4k. Values
                after a comma, it will apply to writes only. In other words,
                the format is either bs=read_and_write or bs=read,write.
                bs=4k,8k will thus use 4k blocks for reads, and 8k blocks
                after a comma, it will apply to writes only. In other words,
                the format is either bs=read_and_write or bs=read,write.
                bs=4k,8k will thus use 4k blocks for reads, and 8k blocks

-               for writes.
+               for writes. If you only wish to set the write size, you
+               can do so by passing an empty read size - bs=,8k will set
+               8k for writes and leave the read default value.

 
 bsrange=irange Instead of giving a single block size, specify a range
                and fio will mix the issued io block sizes. The issued
 
 bsrange=irange Instead of giving a single block size, specify a range
                and fio will mix the issued io block sizes. The issued


@@ -262,6 +264,10 @@ ioengine=str       Defines how the job issues io to the file. The following
                                we use read(2) and write(2) for asynchronous
                                io.
 
                                we use read(2) and write(2) for asynchronous
                                io.
 

+                       null    Doesn't transfer any data, just pretends
+                               to. This is mainly used to exercise fio
+                               itself and for debugging/testing purposes.
+

 iodepth=int    This defines how many io units to keep in flight against
                the file. The default is 1 for each file defined in this
                job, can be overridden with a larger value for higher
 iodepth=int    This defines how many io units to keep in flight against
                the file. The default is 1 for each file defined in this
                job, can be overridden with a larger value for higher


@@ -351,11 +357,32 @@ mem=str           Fio can use various types of memory as the io unit buffer.
                        shm     Use shared memory as the buffers. Allocated
                                through shmget(2).
 
                        shm     Use shared memory as the buffers. Allocated
                                through shmget(2).
 

+                       shmhuge Same as shm, but use huge pages as backing.
+

                        mmap    Use anonymous memory maps as the buffers.
                                Allocated through mmap(2).
 
                        mmap    Use anonymous memory maps as the buffers.
                                Allocated through mmap(2).
 

+                       mmaphuge Use a memory mapped huge file as the buffer
+                               backing. Append filename after mmaphuge, ala
+                               mem=mmaphuge:/hugetlbfs/file
+

                The area allocated is a function of the maximum allowed
                The area allocated is a function of the maximum allowed

-               bs size for the job, multiplied by the io depth given.
+               bs size for the job, multiplied by the io depth given. Note
+               that for shmhuge and mmaphuge to work, the system must have
+               free huge pages allocated. This can normally be checked
+               and set by reading/writing /proc/sys/vm/nr_hugepages on a
+               Linux system. Fio assumes a huge page is 4MiB in size. So
+               to calculate the number of huge pages you need for a given
+               job file, add up the io depth of all jobs (normally one unless
+               iodepth= is used) and multiply by the maximum bs set. Then
+               divide that number by the huge page size. You can see the
+               size of the huge pages in /proc/meminfo. If no huge pages
+               are allocated by having a non-zero number in nr_hugepages,
+               using mmaphuge or shmhuge will fail.
+
+               mmaphuge also needs to have hugetlbfs mounted and the file
+               location should point there. So if it's mounted in /huge,
+               you would use mem=mmaphuge:/huge/somefile.

 
 exitall                When one job finishes, terminate the rest. The default is
                to wait for each job to finish, sometimes that is not the
 
 exitall                When one job finishes, terminate the rest. The default is
                to wait for each job to finish, sometimes that is not the