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@xxxxxxxxxx>
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@xxxxxxxxxx
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
Fixes: d0f5a85442d1 ("shmem: update documentation")
Fixes: 2c6efe9cf2d7 ("shmem: add support to ignore swap")
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: Luis Chamberlain <mcgrof@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
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@xxxxxxxxxx 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
