mm hugetlb x86: add hugepage support to pagemap

Hi,

Most callers of pmd_none_or_clear_bad() check whether the target page is in a hugepage or not, but mincore() and walk_page_range() do not check it. So if we read /proc/pid/pagemap for the hugepage on x86 machine, the hugepage memory is leaked as shown below. This patch fixes it by extending pagemap interface to support hugepages.

I split this fix into two patches. The first patch just adds the check for hugepages, and the second patch adds a new member to struct mm_walk to handle the hugepages.

 fs/proc/task_mmu.c |   43 +++++++++++++++++++++++++++++++++++++++++++
 include/linux/mm.h |    3 +++
 mm/pagewalk.c      |   29 ++++++++++++++++++++++++++++-
 3 files changed, 74 insertions(+), 1 deletions(-)

Details
=======
My test program (leak_pagemap) works as follows:
- creat() and mmap() a file on hugetlbfs (file size is 200MB == 100 hugepages,)
- read()/write() something on it,
- call page-types with option -p,
- munmap() and unlink() the file on hugetlbfs

Without my patches
------------------

$ cat /proc/meminfo |grep "HugePage"
HugePages_Total:    1000
HugePages_Free:     1000
HugePages_Rsvd:        0
HugePages_Surp:        0
$ ./leak_pagemap
             flags page-count       MB  symbolic-flags                     long-symbolic-flags
0x0000000000000000          1        0  __________________________________ 
0x0000000000000804          1        0  __R________M______________________ referenced,mmap
0x000000000000086c         81        0  __RU_lA____M______________________ referenced,uptodate,lru,active,mmap
0x0000000000005808          5        0  ___U_______Ma_b___________________ uptodate,mmap,anonymous,swapbacked
0x0000000000005868         12        0  ___U_lA____Ma_b___________________ uptodate,lru,active,mmap,anonymous,swapbacked
0x000000000000586c          1        0  __RU_lA____Ma_b___________________ referenced,uptodate,lru,active,mmap,anonymous,swapbacked
             total        101        0
$ cat /proc/meminfo |grep "HugePage"
HugePages_Total:    1000
HugePages_Free:      900
HugePages_Rsvd:        0
HugePages_Surp:        0
$ ls /hugetlbfs/
$ 

The output of page-types don't show any hugepage, and 100 hugepages are accounted as used while there is no file on hugetlbfs

With my patches
---------------

$ cat /proc/meminfo |grep "HugePage"
HugePages_Total:    1000
HugePages_Free:     1000
HugePages_Rsvd:        0
HugePages_Surp:        0
$ ./leak_pagemap 
             flags page-count       MB  symbolic-flags                     long-symbolic-flags
0x0000000000000000          1        0  __________________________________ 
0x0000000000030000      51100      199  ________________TG________________ compound_tail,huge
0x0000000000028018        100        0  ___UD__________H_G________________ uptodate,dirty,compound_head,huge
0x0000000000000804          1        0  __R________M______________________ referenced,mmap
0x000000000000080c          1        0  __RU_______M______________________ referenced,uptodate,mmap
0x000000000000086c         80        0  __RU_lA____M______________________ referenced,uptodate,lru,active,mmap
0x0000000000005808          4        0  ___U_______Ma_b___________________ uptodate,mmap,anonymous,swapbacked
0x0000000000005868         12        0  ___U_lA____Ma_b___________________ uptodate,lru,active,mmap,anonymous,swapbacked
0x000000000000586c          1        0  __RU_lA____Ma_b___________________ referenced,uptodate,lru,active,mmap,anonymous,swapbacked
             total      51300      200
$ cat /proc/meminfo |grep "HugePage"
HugePages_Total:    1000
HugePages_Free:     1000
HugePages_Rsvd:        0
HugePages_Surp:        0
$ ls /hugetlbfs
$ 

The output of page-types shows 51200 pages contributing to hugepages, containing 100 head pages and 51100 tail pages as expected. And no memory leaks.

Thanks,
Naoya Horiguchi

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I kind of dislike the practice of putting all the changelog in patch [0/n] and then leaving the patches themselves practically unchangelogged. Because

a) Someone (ie: me) needs to go and shuffle all the text around so that the information gets itself into the git record. We don't add changelog-only commits to git!

b) Someone (ie: me) might decide to backport a subset of the patches into -stable. Now someone (ie: me) needs to carve up the changelogs so that the pieces which go into -stable still make standalone sense.

I'm not sure that I did this particularly well in this case. Oh well.

Please confirm that mm-hugetlb-fix-hugepage-memory-leak-in-walk_page_range.patch is suitable for a -stable backport without inclusion of mm-hugetlb-add-hugepage-support-to-pagemap.patch. I think it is.

Sorry, I agree.

I think that's OK.

Thanks,
Naoya Horiguchi

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