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>

1 files changed, 27 insertions, 13 deletions

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 4379c6ac3265..f4d123b57c5b 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -834,12 +834,15 @@
 			See also Documentation/networking/decnet.txt.
 
 	default_hugepagesz=
-			[same as hugepagesz=] The size of the default
-			HugeTLB page size. This is the size represented by
-			the legacy /proc/ hugepages APIs, used for SHM, and
-			default size when mounting hugetlbfs filesystems.
-			Defaults to the default architecture's huge page size
-			if not specified.
+			[HW] The size of the default HugeTLB page. This is
+			the size represented by the legacy /proc/ hugepages
+			APIs.  In addition, this is the default hugetlb size
+			used for shmget(), mmap() and mounting hugetlbfs
+			filesystems.  If not specified, defaults to the
+			architecture's default huge page size.  Huge page
+			sizes are architecture dependent.  See also
+			Documentation/admin-guide/mm/hugetlbpage.rst.
+			Format: size[KMG]
 
 	deferred_probe_timeout=
 			[KNL] Debugging option to set a timeout in seconds for
@@ -1479,13 +1482,24 @@
 			hugepages using the cma allocator. If enabled, the
 			boot-time allocation of gigantic hugepages is skipped.
 
-	hugepages=	[HW,X86-32,IA-64] HugeTLB pages to allocate at boot.
-	hugepagesz=	[HW,IA-64,PPC,X86-64] The size of the HugeTLB pages.
-			On x86-64 and powerpc, this option can be specified
-			multiple times interleaved with hugepages= to reserve
-			huge pages of different sizes. Valid pages sizes on
-			x86-64 are 2M (when the CPU supports "pse") and 1G
-			(when the CPU supports the "pdpe1gb" cpuinfo flag).
+	hugepages=	[HW] Number of HugeTLB pages to allocate at boot.
+			If this follows hugepagesz (below), it specifies
+			the number of pages of hugepagesz to be allocated.
+			If this is the first HugeTLB parameter on the command
+			line, it specifies the number of pages to allocate for
+			the default huge page size.  See also
+			Documentation/admin-guide/mm/hugetlbpage.rst.
+			Format: <integer>
+
+	hugepagesz=
+			[HW] The size of the HugeTLB pages.  This is used in
+			conjunction with hugepages (above) to allocate huge
+			pages of a specific size at boot.  The pair
+			hugepagesz=X hugepages=Y can be specified once for
+			each supported huge page size. Huge page sizes are
+			architecture dependent.  See also
+			Documentation/admin-guide/mm/hugetlbpage.rst.
+			Format: size[KMG]
 
 	hung_task_panic=
 			[KNL] Should the hung task detector generate panics.