+ tmpfs-fix-documentation-of-noswap-and-huge-mount-options.patch added to mm-hotfixes-unstable branch

+ tmpfs-fix-documentation-of-noswap-and-huge-mount-options.patch added to mm-hotfixes-unstable branch

[Andrew Morton]

The patch titled
     Subject: tmpfs: fix Documentation of noswap and huge mount options
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     tmpfs-fix-documentation-of-noswap-and-huge-mount-options.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/tmpfs-fix-documentation-of-noswap-and-huge-mount-options.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Hugh Dickins <hughd@google.com>
Subject: tmpfs: fix Documentation of noswap and huge mount options
Date: Sun, 23 Jul 2023 13:55:00 -0700 (PDT)

The noswap mount option is surely not one of the three options for sizing:
move its description down.

The huge= mount option does not accept numeric values: those are just in
an internal enum.  Delete those numbers, and follow the manpage text more
closely (but there's not yet any fadvise() or fcntl() which applies here).

/sys/kernel/mm/transparent_hugepage/shmem_enabled is hard to describe, and
barely relevant to mounting a tmpfs: just refer to transhuge.rst (while
still using the words deny and force, to help as informal reminders).

Link: https://lkml.kernel.org/r/986cb0bf-9780-354-9bb-4bf57aadbab@google.com
Signed-off-by: Hugh Dickins <hughd@google.com>
Fixes: d0f5a85442d1 ("shmem: update documentation")
Fixes: 2c6efe9cf2d7 ("shmem: add support to ignore swap")
Cc: Christian Brauner <brauner@kernel.org>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 Documentation/filesystems/tmpfs.rst |   47 +++++++++++---------------
 1 file changed, 20 insertions(+), 27 deletions(-)

--- a/Documentation/filesystems/tmpfs.rst~tmpfs-fix-documentation-of-noswap-and-huge-mount-options
+++ a/Documentation/filesystems/tmpfs.rst
@@ -84,8 +84,6 @@ nr_inodes  The maximum number of inodes
            is half of the number of your physical RAM pages, or (on a
            machine with highmem) the number of lowmem RAM pages,
            whichever is the lower.
-noswap     Disables swap. Remounts must respect the original settings.
-           By default swap is enabled.
 =========  ============================================================
 
 These parameters accept a suffix k, m or g for kilo, mega and giga and
@@ -99,36 +97,31 @@ mount with such options, since it allows
 use up all the memory on the machine; but enhances the scalability of
 that instance in a system with many CPUs making intensive use of it.
 
+tmpfs blocks may be swapped out, when there is a shortage of memory.
+tmpfs has a mount option to disable its use of swap:
+
+======  ===========================================================
+noswap  Disables swap. Remounts must respect the original settings.
+        By default swap is enabled.
+======  ===========================================================
+
 tmpfs also supports Transparent Huge Pages which requires a kernel
 configured with CONFIG_TRANSPARENT_HUGEPAGE and with huge supported for
 your system (has_transparent_hugepage(), which is architecture specific).
 The mount options for this are:
 
-======  ============================================================
-huge=0  never: disables huge pages for the mount
-huge=1  always: enables huge pages for the mount
-huge=2  within_size: only allocate huge pages if the page will be
-        fully within i_size, also respect fadvise()/madvise() hints.
-huge=3  advise: only allocate huge pages if requested with
-        fadvise()/madvise()
-======  ============================================================
-
-There is a sysfs file which you can also use to control system wide THP
-configuration for all tmpfs mounts, the file is:
-
-/sys/kernel/mm/transparent_hugepage/shmem_enabled
-
-This sysfs file is placed on top of THP sysfs directory and so is registered
-by THP code. It is however only used to control all tmpfs mounts with one
-single knob. Since it controls all tmpfs mounts it should only be used either
-for emergency or testing purposes. The values you can set for shmem_enabled are:
-
-==  ============================================================
--1  deny: disables huge on shm_mnt and all mounts, for
-    emergency use
--2  force: enables huge on shm_mnt and all mounts, w/o needing
-    option, for testing
-==  ============================================================
+===========  ==============================================================
+huge=never   Do not allocate huge pages.  This is the default.
+huge=always  Attempt to allocate huge page every time a new page is needed.
+huge=within_size Only allocate huge page if it will be fully within i_size.
+             Also respect madvise(2) hints.
+huge=advise  Only allocate huge page if requested with madvise(2).
+===========  ==============================================================
+
+See also Documentation/admin-guide/mm/transhuge.rst, which describes the
+sysfs file /sys/kernel/mm/transparent_hugepage/shmem_enabled: which can
+be used to deny huge pages on all tmpfs mounts in an emergency, or to
+force huge pages on all tmpfs mounts for testing.
 
 tmpfs has a mount option to set the NUMA memory allocation policy for
 all files in that instance (if CONFIG_NUMA is enabled) - which can be
_

Patches currently in -mm which might be from hughd@google.com are

tmpfs-fix-documentation-of-noswap-and-huge-mount-options.patch
shmem-minor-fixes-to-splice-read-implementation.patch
mm-pagewalk-fix-efi_pgt_dump-of-espfix-area.patch
mm-userfaultfd-add-new-uffdio_poison-ioctl-fix.patch
mm-pgtable-add-rcu_read_lock-and-rcu_read_unlocks.patch
mm-pgtable-add-pae-safety-to-__pte_offset_map.patch
arm-adjust_pte-use-pte_offset_map_nolock.patch
powerpc-assert_pte_locked-use-pte_offset_map_nolock.patch
powerpc-add-pte_free_defer-for-pgtables-sharing-page.patch
sparc-add-pte_free_defer-for-pte_t-pgtable_t.patch
s390-add-pte_free_defer-for-pgtables-sharing-page.patch
mm-pgtable-add-pte_free_defer-for-pgtable-as-page.patch
mm-khugepaged-retract_page_tables-without-mmap-or-vma-lock.patch
mm-khugepaged-collapse_pte_mapped_thp-with-mmap_read_lock.patch
mm-khugepaged-delete-khugepaged_collapse_pte_mapped_thps.patch
mm-delete-mmap_write_trylock-and-vma_try_start_write.patch
mm-pgtable-notes-on-pte_offset_map.patch