kernel-fxtec-pro1x/Documentation/sysctl
Vinayak Menon 3aee78b794 mm: make faultaround produce old ptes
Based on Kirill's patch [1].

Currently, faultaround code produces young pte.  This can screw up
vmscan behaviour[2], as it makes vmscan think that these pages are hot
and not push them out on first round.

During sparse file access faultaround gets more pages mapped and all of
them are young. Under memory pressure, this makes vmscan swap out anon
pages instead, or to drop other page cache pages which otherwise stay
resident.

Modify faultaround to produce old ptes if sysctl 'want_old_faultaround_pte'
is set, so they can easily be reclaimed under memory pressure.

This can to some extend defeat the purpose of faultaround on machines
without hardware accessed bit as it will not help us with reducing the
number of minor page faults.

Making the faultaround ptes old results in a unixbench regression for some
architectures [3][4]. But on some architectures like arm64 it is not found
to cause any regression.

unixbench shell8 scores on arm64 v8.2 hardware with CONFIG_ARM64_HW_AFDBM
enabled  (5 runs min, max, avg):
Base: (741,748,744)
With this patch: (739,748,743)

So by default produce young ptes and provide a sysctl option to make the
ptes old.

[1] https://marc.info/?l=linux-mm&m=146348837703148
[2] https://lkml.org/lkml/2016/4/18/612
[3] https://marc.info/?l=linux-kernel&m=146582237922378&w=2
[4] https://marc.info/?l=linux-mm&m=146589376909424&w=2

Change-Id: I193185cc953bc33a44fc24963a9df9e555906d95
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Patch-mainline: linux-mm @ Fri, 19 Jan 2018 17:24:54
[vinmenon@codeaurora.org: enable by default since arm works well
with old fault_around ptes + edit the links in commit message to
fix checkpatch issues]
Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>
[swatsrid@codeaurora.org: Fix merge conflicts]
Signed-off-by: Swathi Sridhar <swatsrid@codeaurora.org>
2019-01-22 12:28:57 -08:00
..
00-INDEX
abi.txt
fs.txt namei: allow restricted O_CREAT of FIFOs and regular files 2018-08-23 18:48:43 -07:00
kernel.txt sysctl: add boot_reason and cold_boot sysctl entries for arm64 2018-11-08 14:26:44 -08:00
net.txt
README
sunrpc.txt
user.txt
vm.txt mm: make faultaround produce old ptes 2019-01-22 12:28:57 -08:00

Documentation for /proc/sys/		kernel version 2.2.10
	(c) 1998, 1999,  Rik van Riel <riel@nl.linux.org>

'Why', I hear you ask, 'would anyone even _want_ documentation
for them sysctl files? If anybody really needs it, it's all in
the source...'

Well, this documentation is written because some people either
don't know they need to tweak something, or because they don't
have the time or knowledge to read the source code.

Furthermore, the programmers who built sysctl have built it to
be actually used, not just for the fun of programming it :-)

==============================================================

Legal blurb:

As usual, there are two main things to consider:
1. you get what you pay for
2. it's free

The consequences are that I won't guarantee the correctness of
this document, and if you come to me complaining about how you
screwed up your system because of wrong documentation, I won't
feel sorry for you. I might even laugh at you...

But of course, if you _do_ manage to screw up your system using
only the sysctl options used in this file, I'd like to hear of
it. Not only to have a great laugh, but also to make sure that
you're the last RTFMing person to screw up.

In short, e-mail your suggestions, corrections and / or horror
stories to: <riel@nl.linux.org>

Rik van Riel.

==============================================================

Introduction:

Sysctl is a means of configuring certain aspects of the kernel
at run-time, and the /proc/sys/ directory is there so that you
don't even need special tools to do it!
In fact, there are only four things needed to use these config
facilities:
- a running Linux system
- root access
- common sense (this is especially hard to come by these days)
- knowledge of what all those values mean

As a quick 'ls /proc/sys' will show, the directory consists of
several (arch-dependent?) subdirs. Each subdir is mainly about
one part of the kernel, so you can do configuration on a piece
by piece basis, or just some 'thematic frobbing'.

The subdirs are about:
abi/		execution domains & personalities
debug/		<empty>
dev/		device specific information (eg dev/cdrom/info)
fs/		specific filesystems
		filehandle, inode, dentry and quota tuning
		binfmt_misc <Documentation/admin-guide/binfmt-misc.rst>
kernel/		global kernel info / tuning
		miscellaneous stuff
net/		networking stuff, for documentation look in:
		<Documentation/networking/>
proc/		<empty>
sunrpc/		SUN Remote Procedure Call (NFS)
vm/		memory management tuning
		buffer and cache management
user/		Per user per user namespace limits

These are the subdirs I have on my system. There might be more
or other subdirs in another setup. If you see another dir, I'd
really like to hear about it :-)