Tag ABD pages for exclusion in kernel crash dumps

[don-brady]

Motivation and Context

Tag the ABD data pages so that they can be identified for exclusion from kernel crash dumps. Eliminating the zfs file data allows for significantly smaller crash dump files. Note that ZFS in illumos has always excluded the zfs data pages from a kernel crash dump.

Description

This change tags ARC scatter data pages so they can be identified from the makedumpfile(8) command. That command is used to create smaller dump files by ignoring some memory regions and using compression. It already filters file data from the VFS page cache and will now be able to exclude ZFS file data pages from the dump file.

A corresponding change to makeumpfile(8) is required to identify ZFS data pages.

How Has This Been Tested?

ztest

generated kernel crash dumps using a modified makeumpfile and confirmed that zfs data pages were being excluded.

Sample summary:

  Excluded pages   : 0x0000000000165a4e
    Pages filled with zero  : 0x000000000000bda5
    Non-private cache pages : 0x000000000000a296
    Private cache pages     : 0x0000000000000007
    ZFS ARC file data pages : 0x00000000000802e8
    User process data pages : 0x0000000000066b3e
    Free pages              : 0x0000000000068be6
    Hwpoison pages          : 0x0000000000000000
  Remaining pages  : 0x000000000003a541
  (The number of pages is reduced to 14%.)
Memory Hole     : 0x00000000000e0071
--------------------------------------------------
Total pages     : 0x0000000000280000

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the ZFS on Linux code style requirements.
• I have updated the documentation accordingly.
• I have read the contributing document.
• I have added tests to cover my changes.
• All new and existing tests passed.
• All commit messages are properly formatted and contain Signed-off-by.

[behlendorf]

You're going to need to define a smaller value for 32-bit platforms to resolve the build failures on arm/ppc/i386.

/var/lib/buildbot/slaves/buildslave1/Debian_8_arm__BUILD_/build/zfs/module/zfs/abd.c: In function ‘abd_mark_zfs_page’:
include/linux/mm.h:319:54: error: large integer implicitly truncated to unsigned type [-Werror=overflow]
 #define set_page_private(page, v) ((page)->private = (v))
                                                      ^
/var/lib/buildbot/slaves/buildslave1/Debian_8_arm__BUILD_/build/zfs/module/zfs/abd.c:264:2: note: in expansion of macro ‘set_page_private’
  set_page_private(page, ABD_FILE_CACHE_PAGE);

[don-brady]

I limited the page tagging to 64-bit platforms.

[codecov]

Codecov Report

Merging #8899 into master will increase coverage by 0.21%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #8899      +/-   ##
==========================================
+ Coverage   72.47%   72.69%   +0.21%     
==========================================
  Files         371      371              
  Lines      119441   119449       +8     
==========================================
+ Hits        86569    86830     +261     
+ Misses      32872    32619     -253

Flag	Coverage Δ
#kernel	72.45% <100%> (+0.06%)	⬆️
#user	63.45% <ø> (+0.35%)	⬆️

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