fio uses posix_fadvise, but can only take two values :
if (td->o.invalidate_cache && file_invalidate_cache(td, f))
goto err;
if (td->o.fadvise_hint &&
(f->filetype == FIO_TYPE_BD || f->filetype == FIO_TYPE_FILE)) {
int flags;
if (td_random(td))
flags = POSIX_FADV_RANDOM;
else
flags = POSIX_FADV_SEQUENTIAL;
if (posix_fadvise(f->fd, f->file_offset, f->io_size, flags) < 0) {
td_verror(td, errno, "fadvise");
goto err;
}
}
But it can take many values, from linux/fadvise.h:
#define POSIX_FADV_NORMAL 0 /* No further special treatment. */
#define POSIX_FADV_RANDOM 1 /* Expect random page references. */
#define POSIX_FADV_SEQUENTIAL 2 /* Expect sequential page references. */
#define POSIX_FADV_WILLNEED 3 /* Will need these pages. */
...
#define POSIX_FADV_DONTNEED 4 /* Don't need these pages. */
#define POSIX_FADV_NOREUSE 5 /* Data will be accessed once. */
POSIX_FADV_NOREUSE have no effect on current kernel (https://github.com/torvalds/linux/blob/master/mm/fadvise.c#L115) but DONTNEED is interesting as it allow
to flush page cache after use It allows to do bench with machines with huge memory without having to bench huge files, and without using directio that is a strange beast. But it needs to be call right after use.
It's used in file_invalidate_cache but this function seems to be call once, when file is open for the first time.
Is there any plan to support it ?
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