Vinayak Menon
3aee78b794
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>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.