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A mirror of the official Linux kernel repository just in case
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Johannes Weiner 8c7829b04c mm: fix false-positive OVERCOMMIT_GUESS failures 
With the default overcommit==guess we occasionally run into mmap
rejections despite plenty of memory that would get dropped under
pressure but just isn't accounted reclaimable. One example of this is
dying cgroups pinned by some page cache. A previous case was auxiliary
path name memory associated with dentries; we have since annotated
those allocations to avoid overcommit failures (see d79f7aa496 ("mm:
treat indirectly reclaimable memory as free in overcommit logic")).

But trying to classify all allocated memory reliably as reclaimable
and unreclaimable is a bit of a fool's errand. There could be a myriad
of dependencies that constantly change with kernel versions.

It becomes even more questionable of an effort when considering how
this estimate of available memory is used: it's not compared to the
system-wide allocated virtual memory in any way. It's not even
compared to the allocating process's address space. It's compared to
the single allocation request at hand!

So we have an elaborate left-hand side of the equation that tries to
assess the exact breathing room the system has available down to a
page - and then compare it to an isolated allocation request with no
additional context. We could fail an allocation of N bytes, but for
two allocations of N/2 bytes we'd do this elaborate dance twice in a
row and then still let N bytes of virtual memory through. This doesn't
make a whole lot of sense.

Let's take a step back and look at the actual goal of the
heuristic. From the documentation:

   Heuristic overcommit handling. Obvious overcommits of address
   space are refused. Used for a typical system. It ensures a
   seriously wild allocation fails while allowing overcommit to
   reduce swap usage.  root is allowed to allocate slightly more
   memory in this mode. This is the default.

If all we want to do is catch clearly bogus allocation requests
irrespective of the general virtual memory situation, the physical
memory counter-part doesn't need to be that complicated, either.

When in GUESS mode, catch wild allocations by comparing their request
size to total amount of ram and swap in the system.

Link: http://lkml.kernel.org/r/20190412191418.26333-1-hannes@cmpxchg.org
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Roman Gushchin <guro@fb.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2019-05-14 09:47:50 -07:00
arch mm/memory_hotplug: make __remove_pages() and arch_remove_memory() never fail 2019-05-14 09:47:50 -07:00
block for-5.2/block-20190507 2019-05-07 18:14:36 -07:00
certs
crypto Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next 2019-05-07 22:03:58 -07:00
Documentation mm/hmm: add default fault flags to avoid the need to pre-fill pfns arrays 2019-05-14 09:47:48 -07:00
drivers mm/memory_hotplug: make unregister_memory_section() never fail 2019-05-14 09:47:49 -07:00
fs mm/mmu_notifier: use correct mmu_notifier events for each invalidation 2019-05-14 09:47:49 -07:00
include mm/memory_hotplug: make __remove_pages() and arch_remove_memory() never fail 2019-05-14 09:47:50 -07:00
init init: free_initmem: poison freed init memory 2019-05-14 09:47:47 -07:00
ipc Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next 2019-05-07 22:03:58 -07:00
kernel mm, memory_hotplug: provide a more generic restrictions for memory hotplug 2019-05-14 09:47:49 -07:00
lib mm/gup: change GUP fast to use flags rather than a write 'bool' 2019-05-14 09:47:46 -07:00
LICENSES
mm mm: fix false-positive OVERCOMMIT_GUESS failures 2019-05-14 09:47:50 -07:00
net mm/gup: change GUP fast to use flags rather than a write 'bool' 2019-05-14 09:47:46 -07:00
samples samples: add .gitignore for pidfd-metadata 2019-05-10 11:50:52 +02:00
scripts A reasonably busy cycle for docs, including: 2019-05-08 12:42:50 -07:00
security tomoyo: Don't emit WARNING: string while fuzzing testing. 2019-05-10 14:58:35 -07:00
sound sound updates for 5.2-rc1 2019-05-09 08:26:55 -07:00
tools powerpc updates for 5.2 2019-05-10 05:29:27 -07:00
usr
virt mm/mmu_notifier: convert user range->blockable to helper function 2019-05-14 09:47:49 -07:00
.clang-format
.cocciconfig
.get_maintainer.ignore
.gitattributes
.gitignore .gitignore: add more all*.config patterns 2019-05-08 09:47:46 +09:00
.mailmap A reasonably busy cycle for docs, including: 2019-05-08 12:42:50 -07:00
COPYING
CREDITS
Kbuild
Kconfig
MAINTAINERS MAINTAINERS: add Joseph as ocfs2 co-maintainer 2019-05-14 09:47:44 -07:00
Makefile Kbuild updates for v5.2 2019-05-08 12:25:12 -07:00
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.

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.