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The source for the Linux kernel used in Windows Subsystem for Linux 2 (WSL2)
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Michal Hocko 29ef680ae7 memcg, oom: move out_of_memory back to the charge path 
Commit 3812c8c8f3 ("mm: memcg: do not trap chargers with full
callstack on OOM") has changed the ENOMEM semantic of memcg charges.
Rather than invoking the oom killer from the charging context it delays
the oom killer to the page fault path (pagefault_out_of_memory).  This
in turn means that many users (e.g.  slab or g-u-p) will get ENOMEM when
the corresponding memcg hits the hard limit and the memcg is is OOM.
This is behavior is inconsistent with !memcg case where the oom killer
is invoked from the allocation context and the allocator keeps retrying
until it succeeds.

The difference in the behavior is user visible.  mmap(MAP_POPULATE)
might result in not fully populated ranges while the mmap return code
doesn't tell that to the userspace.  Random syscalls might fail with
ENOMEM etc.

The primary motivation of the different memcg oom semantic was the
deadlock avoidance.  Things have changed since then, though.  We have an
async oom teardown by the oom reaper now and so we do not have to rely
on the victim to tear down its memory anymore.  Therefore we can return
to the original semantic as long as the memcg oom killer is not handed
over to the users space.

There is still one thing to be careful about here though.  If the oom
killer is not able to make any forward progress - e.g.  because there is
no eligible task to kill - then we have to bail out of the charge path
to prevent from same class of deadlocks.  We have basically two options
here.  Either we fail the charge with ENOMEM or force the charge and
allow overcharge.  The first option has been considered more harmful
than useful because rare inconsistencies in the ENOMEM behavior is hard
to test for and error prone.  Basically the same reason why the page
allocator doesn't fail allocations under such conditions.  The later
might allow runaways but those should be really unlikely unless somebody
misconfigures the system.  E.g.  allowing to migrate tasks away from the
memcg to a different unlimited memcg with move_charge_at_immigrate
disabled.

Link: http://lkml.kernel.org/r/20180628151101.25307-1-mhocko@kernel.org
Signed-off-by: Michal Hocko <mhocko@suse.com>
Acked-by: Greg Thelen <gthelen@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Shakeel Butt <shakeelb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
 		2018-08-17 16:20:30 -07:00
Documentation tools/vm/page-types.c: add support for idle page tracking 2018-08-17 16:20:28 -07:00
LICENSES LICENSES: Add Linux-OpenIB license text 2018-04-27 16:41:53 -06:00
arch mm: convert return type of handle_mm_fault() caller to vm_fault_t 2018-08-17 16:20:28 -07:00
block for-4.19/block-20180812 2018-08-14 10:23:25 -07:00
certs Replace magic for trusting the secondary keyring with #define 2018-08-16 09:57:20 -07:00
crypto Replace magic for trusting the secondary keyring with #define 2018-08-16 09:57:20 -07:00
drivers mm: provide a fallback for PAGE_KERNEL_RO for architectures 2018-08-17 16:20:29 -07:00
firmware kbuild: remove all dummy assignments to obj- 2017-11-18 11:46:06 +09:00
fs fs, mm: account buffer_head to kmemcg 2018-08-17 16:20:30 -07:00
include memcg, oom: move out_of_memory back to the charge path 2018-08-17 16:20:30 -07:00
init Consolidation of Kconfig files by Christoph Hellwig. 2018-08-15 13:05:12 -07:00
ipc Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next 2018-08-15 15:04:25 -07:00
kernel kernel/memremap, kasan: make ZONE_DEVICE with work with KASAN 2018-08-17 16:20:30 -07:00
lib SCSI misc on 20180815 2018-08-15 22:06:26 -07:00
mm memcg, oom: move out_of_memory back to the charge path 2018-08-17 16:20:30 -07:00
net Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2018-08-15 16:01:47 -07:00
samples Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next 2018-08-15 15:04:25 -07:00
scripts scripts: add Python 3 compatibility to spdxcheck.py 2018-08-17 16:20:27 -07:00
security Merge branch 'next-integrity' of git://git.kernel.org/pub/scm/linux/kernel/git/jmorris/linux-security 2018-08-15 22:54:12 -07:00
sound ALSA: update dell-wmi mic-mute registration to new world order 2018-08-15 19:08:10 -07:00
tools tools/vm/page-types.c: add support for idle page tracking 2018-08-17 16:20:28 -07:00
usr kbuild: rename built-in.o to built-in.a 2018-03-26 02:01:19 +09:00
virt arm64 updates for 4.19 2018-08-14 16:39:13 -07:00
.clang-format clang-format: Set IndentWrappedFunctionNames false 2018-08-01 18:38:51 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Add hch to .get_maintainer.ignore 2015-08-21 14:30:10 -07:00
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Kbuild updates for v4.17 (2nd) 2018-04-15 17:21:30 -07:00
.mailmap mailmap: remap some of my email addresses to kernel.org address 2018-08-06 13:15:16 -04:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS 9p: remove Ron Minnich from MAINTAINERS 2018-08-17 16:20:26 -07:00
Kbuild Kbuild updates for v4.15 2017-11-17 17:45:29 -08:00
Kconfig kconfig: move the "Executable file formats" menu to fs/Kconfig.binfmt 2018-08-02 08:06:55 +09:00
MAINTAINERS 9p: add Dominique Martinet to MAINTAINERS 2018-08-17 16:20:27 -07:00
Makefile Kconfig updates for v4.19 2018-08-15 12:50:10 -07:00
README Docs: Added a pointer to the formatted docs to README 2018-03-21 09:02:53 -06:00

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.