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tmpfs: fix Documentation of noswap and huge mount options
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). [rdunlap@infradead.org: fixup Docs table for huge mount options] Link: https://lkml.kernel.org/r/20230725052333.26857-1-rdunlap@infradead.org Link: https://lkml.kernel.org/r/986cb0bf-9780-354-9bb-4bf57aadbab@google.com Signed-off-by: Hugh Dickins <hughd@google.com> Signed-off-by: Randy Dunlap <rdunlap@infradead.org> Fixes:d0f5a85442
("shmem: update documentation") Fixes:2c6efe9cf2
("shmem: add support to ignore swap") Reviewed-by: Luis Chamberlain <mcgrof@kernel.org> Cc: Christian Brauner <brauner@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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@ -84,8 +84,6 @@ nr_inodes The maximum number of inodes for this instance. The default
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is half of the number of your physical RAM pages, or (on a
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machine with highmem) the number of lowmem RAM pages,
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whichever is the lower.
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noswap Disables swap. Remounts must respect the original settings.
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By default swap is enabled.
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========= ============================================================
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These parameters accept a suffix k, m or g for kilo, mega and giga and
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@ -99,36 +97,31 @@ mount with such options, since it allows any user with write access to
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use up all the memory on the machine; but enhances the scalability of
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that instance in a system with many CPUs making intensive use of it.
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tmpfs blocks may be swapped out, when there is a shortage of memory.
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tmpfs has a mount option to disable its use of swap:
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====== ===========================================================
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noswap Disables swap. Remounts must respect the original settings.
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By default swap is enabled.
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====== ===========================================================
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tmpfs also supports Transparent Huge Pages which requires a kernel
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configured with CONFIG_TRANSPARENT_HUGEPAGE and with huge supported for
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your system (has_transparent_hugepage(), which is architecture specific).
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The mount options for this are:
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====== ============================================================
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huge=0 never: disables huge pages for the mount
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huge=1 always: enables huge pages for the mount
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huge=2 within_size: only allocate huge pages if the page will be
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fully within i_size, also respect fadvise()/madvise() hints.
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huge=3 advise: only allocate huge pages if requested with
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fadvise()/madvise()
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====== ============================================================
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================ ==============================================================
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huge=never Do not allocate huge pages. This is the default.
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huge=always Attempt to allocate huge page every time a new page is needed.
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huge=within_size Only allocate huge page if it will be fully within i_size.
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Also respect madvise(2) hints.
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huge=advise Only allocate huge page if requested with madvise(2).
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================ ==============================================================
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There is a sysfs file which you can also use to control system wide THP
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configuration for all tmpfs mounts, the file is:
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/sys/kernel/mm/transparent_hugepage/shmem_enabled
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This sysfs file is placed on top of THP sysfs directory and so is registered
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by THP code. It is however only used to control all tmpfs mounts with one
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single knob. Since it controls all tmpfs mounts it should only be used either
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for emergency or testing purposes. The values you can set for shmem_enabled are:
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== ============================================================
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-1 deny: disables huge on shm_mnt and all mounts, for
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emergency use
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-2 force: enables huge on shm_mnt and all mounts, w/o needing
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option, for testing
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== ============================================================
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See also Documentation/admin-guide/mm/transhuge.rst, which describes the
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sysfs file /sys/kernel/mm/transparent_hugepage/shmem_enabled: which can
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be used to deny huge pages on all tmpfs mounts in an emergency, or to
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force huge pages on all tmpfs mounts for testing.
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tmpfs has a mount option to set the NUMA memory allocation policy for
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all files in that instance (if CONFIG_NUMA is enabled) - which can be
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