Add ability to invoke fallocate() FALLOC_FL_KEEP_SIZE.
Linux offers fallocate() and the FALLOC_FL_KEEP_SIZE option as
an alternative to posix_fallocate(). When FALLOC_FL_KEEP_SIZE is
specified for an falloc request going beyond the end of the file,
the requested blocks get preallocated without changing the apparent
size of the file. This is is a commonly recommended use of fallocate()
for workloads performing append writes.
This patch modifies the fallocate option from a boolean option
to a string option accepting none/posix/keep/0/1. 'keep' is only
made available on systems where FALLOC_FL_KEEP_SIZE is available
(i.e., Linux at this time). If specified, fallocate() is used
with FALLOC_FL_KEEP_SIZE set. 'none' disables pre-allocation while
'posix' uses posix_fallocate(). The default behavior remains unchaned,
i.e., invoking posix_fallocate. The settings '0'/'1' are there to
provide backward compatibility for users who had explicitly set the
boolean option.
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
diff --git a/HOWTO b/HOWTO
index 69b8cc6..ee899b8 100644
--- a/HOWTO
+++ b/HOWTO
@@ -354,11 +354,19 @@
internal generator, which is often of better quality and
faster.
-fallocate=bool By default, fio will use fallocate() to advise the system
- of the size of the file we are going to write. This can be
- turned off with fallocate=0. May not be available on all
- supported platforms. If using ZFS on Solaris this must be
- set to 0 because ZFS doesn't support it.
+fallocate=str Whether pre-allocation is performed when laying down files.
+ Accepted values are:
+
+ none Do not pre-allocate space
+ posix Pre-allocate via posix_fallocate()
+ keep Pre-allocate via fallocate() with
+ FALLOC_FL_KEEP_SIZE set
+ 0 Backward-compatible alias for 'none'
+ 1 Backward-compatible alias for 'posix'
+
+ May not be available on all supported platforms. 'keep' is only
+ available on Linux.If using ZFS on Solaris this must be set to
+ 'none' because ZFS doesn't support it. Default: 'posix'.
fadvise_hint=bool By default, fio will use fadvise() to advise the kernel
on what IO patterns it is likely to issue. Sometimes you