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The MAP_HUGETLB ("-H" option) of gup_benchmark fails:
$ sudo ./gup_benchmark -H
mmap: Invalid argument
This is because gup_benchmark.c is passing in a file descriptor to
mmap(), but the fd came from opening up the /dev/zero file. This
confuses the mmap syscall implementation, which thinks that, if the
caller did not specify MAP_ANONYMOUS, then the file must be a huge page
file. So it attempts to verify that the file really is a huge page
file, as you can see here:
ksys_mmap_pgoff()
{
if (!(flags & MAP_ANONYMOUS)) {
retval = -EINVAL;
if (unlikely(flags & MAP_HUGETLB && !is_file_hugepages(file)))
goto out_fput; /* THIS IS WHERE WE END UP */
else if (flags & MAP_HUGETLB) {
...proceed normally, /dev/zero is ok here...
...and of course is_file_hugepages() returns "false" for the /dev/zero
file.
The problem is that the user space program, gup_benchmark.c, really just
wants anonymous memory here. The simplest way to get that is to pass
MAP_ANONYMOUS whenever MAP_HUGETLB is specified, so that's what this
patch does.
Link: http://lkml.kernel.org/r/20191021212435.398153-2-jhubbard@nvidia.com
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Jérôme Glisse <jglisse@redhat.com>
Cc: Keith Busch <keith.busch@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.