WSL2-Linux-Kernel

The source for the Linux kernel used in Windows Subsystem for Linux 2 (WSL2)

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Mel Gorman 37a4094e82 mremap: remove LATENCY_LIMIT from mremap to reduce the number of TLB shootdowns Commit `5d1904204c` ("mremap: fix race between mremap() and page cleanning") fixed races between mremap and other operations for both file-backed and anonymous mappings. The file-backed was the most critical as it allowed the possibility that data could be changed on a physical page after page_mkclean returned which could trigger data loss or data integrity issues. A customer reported that the cost of the TLBs for anonymous regressions was excessive and resulting in a 30-50% drop in performance overall since this commit on a microbenchmark. Unfortunately I neither have access to the test-case nor can I describe what it does other than saying that mremap operations dominate heavily. This patch removes the LATENCY_LIMIT to handle TLB flushes on a PMD boundary instead of every 64 pages to reduce the number of TLB shootdowns by a factor of 8 in the ideal case. LATENCY_LIMIT was almost certainly used originally to limit the PTL hold times but the latency savings are likely offset by the cost of IPIs in many cases. This patch is not reported to completely restore performance but gets it within an acceptable percentage. The given metric here is simply described as "higher is better". Baseline that was known good 002: Metric: 91.05 004: Metric: 109.45 008: Metric: 73.08 016: Metric: 58.14 032: Metric: 61.09 064: Metric: 57.76 128: Metric: 55.43 Current 001: Metric: 54.98 002: Metric: 56.56 004: Metric: 41.22 008: Metric: 35.96 016: Metric: 36.45 032: Metric: 35.71 064: Metric: 35.73 128: Metric: 34.96 With patch 001: Metric: 61.43 002: Metric: 81.64 004: Metric: 67.92 008: Metric: 51.67 016: Metric: 50.47 032: Metric: 52.29 064: Metric: 50.01 128: Metric: 49.04 So for low threads, it's not restored but for larger number of threads, it's closer to the "known good" baseline. Using a different mremap-intensive workload that is not representative of the real workload there is little difference observed outside of noise in the headline metrics However, the TLB shootdowns are reduced by 11% on average and at the peak, TLB shootdowns were reduced by 21%. Interrupts were sampled every second while the workload ran to get those figures. It's known that the figures will vary as the non-representative load is non-deterministic. An alternative patch was posted that should have significantly reduced the TLB flushes but unfortunately it does not perform as well as this version on the customer test case. If revisited, the two patches can stack on top of each other. Link: http://lkml.kernel.org/r/20180606183803.k7qaw2xnbvzshv34@techsingularity.net Signed-off-by: Mel Gorman <mgorman@techsingularity.net> Reviewed-by: Andrew Morton <akpm@linux-foundation.org> Cc: Nadav Amit <nadav.amit@gmail.com> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Michal Hocko <mhocko@suse.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Aaron Lu <aaron.lu@intel.com> Cc: Hugh Dickins <hughd@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>		2018-06-15 07:55:24 +09:00
Documentation	platform-drivers-x86 for v4.18-1	2018-06-14 16:30:30 +09:00
LICENSES	…
arch	mm: fix devmem_is_allowed() for sub-page System RAM intersections	2018-06-15 07:55:23 +09:00
block	treewide: Use array_size() in vzalloc()	2018-06-12 16:19:22 -07:00
certs	…
crypto	treewide: Use array_size() in sock_kmalloc()	2018-06-12 16:19:22 -07:00
drivers	SCSI fixes on 20180613	2018-06-14 16:35:32 +09:00
firmware	…
fs	Revert "debugfs: inode: debugfs_create_dir uses mode permission from parent"	2018-06-12 20:52:16 -07:00
include	mm: fix race between kmem_cache destroy, create and deactivate	2018-06-15 07:55:23 +09:00
init	Kbuild updates for v4.18 (2nd)	2018-06-13 08:40:34 -07:00
ipc	treewide: kvmalloc() -> kvmalloc_array()	2018-06-12 16:19:22 -07:00
kernel	mm: check for SIGKILL inside dup_mmap() loop	2018-06-15 07:55:24 +09:00
lib	Kbuild updates for v4.18 (2nd)	2018-06-13 08:40:34 -07:00
mm	mremap: remove LATENCY_LIMIT from mremap to reduce the number of TLB shootdowns	2018-06-15 07:55:24 +09:00
net	- Error path bug fix for overflow tests (Dan)	2018-06-12 18:28:00 -07:00
samples	…
scripts	Kbuild updates for v4.18 (2nd)	2018-06-13 08:40:34 -07:00
security	+ Features	2018-06-14 16:11:28 +09:00
sound	- Error path bug fix for overflow tests (Dan)	2018-06-12 18:28:00 -07:00
tools	Additional power management updates for 4.18-rc1	2018-06-13 07:24:18 -07:00
usr	…
virt	- Error path bug fix for overflow tests (Dan)	2018-06-12 18:28:00 -07:00
.clang-format	…
.cocciconfig	…
.get_maintainer.ignore	…
.gitattributes	…
.gitignore	…
.mailmap	…
COPYING	…
CREDITS	…
Kbuild	…
Kconfig	…
MAINTAINERS	Merge branch 'i2c/for-4.18' of git://git.kernel.org/pub/scm/linux/kernel/git/wsa/linux	2018-06-14 16:21:46 +09:00
Makefile	Kbuild: rename CC_STACKPROTECTOR[_STRONG] config variables	2018-06-14 12:21:18 +09:00
README	…

README

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.