After this patch 'page-types' can walk over a file's mappings and
analyze populated page cache pages mostly without disturbing its state.

It maps chunk of file, marks VMA as MADV_RANDOM to turn off readahead,
pokes VMA via mincore() to determine cached pages, triggers page-fault
only for them, and finally gathers information via pagemap/kpageflags.
Before unmap it marks VMA as MADV_SEQUENTIAL for ignoring reference
bits.

usage: page-types -f <path>

If <path> is directory it will analyse all files in all subdirectories.

Symlinks are not followed as well as mount points.  Hardlinks aren't
handled, they'll be dumped as many times as they are found.  Recursive
walk brings all dentries into dcache and populates page cache of
block-devices aka 'Buffers'.

Probably it's worth to add ioctl for dumping file page cache as array of
PFNs as a replacement for this hackish juggling with
mmap/madvise/mincore/pagemap.  Also recursive walk could be replaced
with dumping cached inodes via some ioctl or debugfs interface followed
by openning them via open_by_handle_at, this would fix hardlinks
handling and unneeded population of dcache and buffers.  This interface
might be used as data source for constructing readahead plans and for
background optimizations of actively used files.

collateral changes:
+ fix 64-bit LFS: define _FILE_OFFSET_BITS instead of _LARGEFILE64_SOURCE
+ replace lseek + read with single pread
+ make show_page_range() reusable after flush

usage example:

  ~/src/linux/tools/vm$ sudo ./page-types -L -f page-types
  foffset offset    flags
  page-types       Inode: 2229277       Size: 89065 (22 pages)
  Modify: Tue Feb 25 12:00:59 2014 (162 seconds ago)
  Access: Tue Feb 25 12:01:00 2014 (161 seconds ago)
  0       3cbf3b     __RU_lA____M________________________
  1       38946a     __RU_lA____M________________________
  2       1a3cec     __RU_lA____M________________________
  3       1a8321     __RU_lA____M________________________
  4       3af7cc     __RU_lA____M________________________
  5       1ed532     __RU_lA_____________________________
  6       2e436a     __RU_lA_____________________________
  7       29a35e     ___U_lA_____________________________
  8       2de86e     ___U_lA_____________________________
  9       3bdfb4     ___U_lA_____________________________
  10      3cd8a3     ___U_lA_____________________________
  11      2afa50     ___U_lA_____________________________
  12      2534c2     ___U_lA_____________________________
  13      1b7a40     ___U_lA_____________________________
  14      17b0be     ___U_lA_____________________________
  15      392b0c     ___U_lA_____________________________
  16      3ba46a     __RU_lA_____________________________
  17      397dc8     ___U_lA_____________________________
  18      1f2a36     ___U_lA_____________________________
  19      21fd30     __RU_lA_____________________________
  20      2c35ba     __RU_l______________________________
  21      20f181     __RU_l______________________________

               flags page-count   MB  symbolic-flags                        long-symbolic-flags
  0x000000000000002c          2    0  __RU_l______________________________  referenced,uptodate,lru
  0x0000000000000068         11    0  ___U_lA_____________________________  uptodate,lru,active
  0x000000000000006c          4    0  __RU_lA_____________________________  referenced,uptodate,lru,active
  0x000000000000086c          5    0  __RU_lA____M________________________  referenced,uptodate,lru,active,mmap
               total         22    0

  ~/src/linux/tools/vm$ sudo ./page-types -f /
               flags page-count     MB  symbolic-flags                        long-symbolic-flags
  0x0000000000000028      21761     85  ___U_l______________________________  uptodate,lru
  0x000000000000002c     127279    497  __RU_l______________________________  referenced,uptodate,lru
  0x0000000000000068      74160    289  ___U_lA_____________________________  uptodate,lru,active
  0x000000000000006c      84469    329  __RU_lA_____________________________  referenced,uptodate,lru,active
  0x000000000000007c          1      0  __RUDlA_____________________________  referenced,uptodate,dirty,lru,active
  0x0000000000000228        370      1  ___U_l___I__________________________  uptodate,lru,reclaim
  0x0000000000000828         49      0  ___U_l_____M________________________  uptodate,lru,mmap
  0x000000000000082c        126      0  __RU_l_____M________________________  referenced,uptodate,lru,mmap
  0x0000000000000868        137      0  ___U_lA____M________________________  uptodate,lru,active,mmap
  0x000000000000086c      12890     50  __RU_lA____M________________________  referenced,uptodate,lru,active,mmap
               total     321242   1254

Signed-off-by: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Fengguang Wu <fengguang.wu@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>