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From: Leonid Moiseichuk <leonid.moiseichuk <at> nokia.com>
Subject: [PATCH 3.2.0-rc1 0/3] Used Memory Meter pseudo-device and related changes in MM
Newsgroups: gmane.linux.kernel
Date: Wednesday 4th January 2012 17:21:53 UTC (over 4 years ago)
The main idea of Used Memory Meter (UMM) is to provide low-cost interface
for user-space to notify about memory consumption using similar approach
does but focusing only on "modified" pages which cannot be fogotten.

The calculation formula in terms of meminfo looks the following:
  UsedMemory = (MemTotal - MemFree - Buffers - Cached - SwapCached) +
                                               (SwapTotal - SwapFree)
It reflects well amount of system memory used in applications in heaps and
shared pages.

Previously (n770..n900) we had lowmem.c [1] which used LSM and did a lot
other things,
n9 implementation based on memcg [2] which has own problems, so the
proposed variant
I hope is the best one for n9:
- Keeps connections from user space
- When amount of modified pages reaches crossed pointed value for
particular connection
  makes POLLIN and allow user-space app to read it and react
- Economic as much as possible, so currently its operates if allocation
higher than 487
  pages or last check happened 250 ms before
Of course if no allocation happened then no activities performed, use-time
must be not affected.

Testing results:
- Checkpatch produced 0 warning
- Sparse does not produce warnings
- One check costs ~20 us or less (could be checked with probe=1 insmod)
- One connection costs 20 bytes in kernel-space  (see observer structure)
for 32-bit variant
- For 10K connections poll update in requested in ~10ms, but for
practically device expected
  to will have about 10 connections (like n9 has now).

Known weak points which I do not know how to fix but will if you have a
brillian idea:
- Having hook in MM is nasty but MM/shrinker cannot be used there and LSM
even worse idea
- If I made 
	$cat /dev/used_memory
  it is produced lines in non-stop mode. Adding position check in umm_read
seems doesn not help,
  so "head -1 /dev/used_memory" should be used if you need to quick check
- Format of output is USED_PAGES:AVAILABLE_PAGES, primitive but enough for
tasks module does

Tested on ARM, x86-32 and x86-64 with and without CONFIG_SWAP. Seems works
in all combinations.
Sorry for wide distributions but list of names were produced by

[1] http://elinux.org/Accurate_Memory_Measurement
[2] http://maemo.gitorious.org/maemo-tools/libmemnotify

Leonid Moiseichuk (3):
  Making si_swapinfo exportable
  MM hook for page allocation and release
  Used Memory Meter pseudo-device module

 drivers/misc/Kconfig  |   12 ++
 drivers/misc/Makefile |    1 +
 drivers/misc/umm.c    |  452
 include/linux/mm.h    |   15 ++
 include/linux/umm.h   |   42 +++++
 mm/Kconfig            |    8 +
 mm/page_alloc.c       |   31 ++++
 mm/swapfile.c         |    3 +
 8 files changed, 564 insertions(+), 0 deletions(-)
 create mode 100644 drivers/misc/umm.c
 create mode 100644 include/linux/umm.h


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