hugetlbfs: clean up command line processing

With all hugetlb page processing done in a single file clean up code.

- Make code match desired semantics
  - Update documentation with semantics
- Make all warnings and errors messages start with 'HugeTLB:'.
- Consistently name command line parsing routines.
- Warn if !hugepages_supported() and command line parameters have
  been specified.
- Add comments to code
  - Describe some of the subtle interactions
  - Describe semantics of command line arguments

This patch also fixes issues with implicitly setting the number of
gigantic huge pages to preallocate.  Previously on X86 command line,

        hugepages=2 default_hugepagesz=1G

would result in zero 1G pages being preallocated and,

        # grep HugePages_Total /proc/meminfo
        HugePages_Total:       0
        # sysctl -a | grep nr_hugepages
        vm.nr_hugepages = 2
        vm.nr_hugepages_mempolicy = 2
        # cat /proc/sys/vm/nr_hugepages
        2

After this patch 2 gigantic pages will be preallocated and all the proc,
sysfs, sysctl and meminfo files will accurately reflect this.

To address the issue with gigantic pages, a small change in behavior was
made to command line processing.  Previously the command line,

        hugepages=128 default_hugepagesz=2M hugepagesz=2M hugepages=256

would result in the allocation of 256 2M huge pages.  The value 128 would
be ignored without any warning.  After this patch, 128 2M pages will be
allocated and a warning message will be displayed indicating the value of
256 is ignored.  This change in behavior is required because allocation of
implicitly specified gigantic pages must be done when the
default_hugepagesz= is encountered for gigantic pages.  Previously the
code waited until later in the boot process (hugetlb_init), to allocate
pages of default size.  However the bootmem allocator required for
gigantic allocations is not available at this time.

Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Tested-by: Sandipan Das <sandipan@linux.ibm.com>
Acked-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>	[s390]
Acked-by: Will Deacon <will@kernel.org>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Christophe Leroy <christophe.leroy@c-s.fr>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Longpeng <longpeng2@huawei.com>
Cc: Mina Almasry <almasrymina@google.com>
Cc: Nitesh Narayan Lal <nitesh@redhat.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Anders Roxell <anders.roxell@linaro.org>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Cc: Qian Cai <cai@lca.pw>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Link: http://lkml.kernel.org/r/20200417185049.275845-5-mike.kravetz@oracle.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

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