mm: hugetlb: proc: check for hugetlb shared PMD in /proc/PID/smaps

Patch series "Fixes for hugetlb mapcount at most 1 for shared PMDs".

This issue of mapcount in hugetlb pages referenced by shared PMDs was
discussed in [1].  The following two patches address user visible behavior
caused by this issue.

[1] https://lore.kernel.org/linux-mm/Y9BF+OCdWnCSilEu@monkey/


This patch (of 2):

A hugetlb page will have a mapcount of 1 if mapped by multiple processes
via a shared PMD.  This is because only the first process increases the
map count, and subsequent processes just add the shared PMD page to their
page table.

page_mapcount is being used to decide if a hugetlb page is shared or
private in /proc/PID/smaps.  Pages referenced via a shared PMD were
incorrectly being counted as private.

To fix, check for a shared PMD if mapcount is 1.  If a shared PMD is found
count the hugetlb page as shared.  A new helper to check for a shared PMD
is added.

[[email protected]: simplification, per David]
[[email protected]: hugetlb.h: include page_ref.h for page_count()]
Link: https://lkml.kernel.org/r/[email protected]
Fixes: 25ee01a2fca0 ("mm: hugetlb: proc: add hugetlb-related fields to /proc/PID/smaps")
Signed-off-by: Mike Kravetz <[email protected]>
Acked-by: Peter Xu <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: James Houghton <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Muchun Song <[email protected]>
Cc: Naoya Horiguchi <[email protected]>
Cc: Vishal Moola (Oracle) <[email protected]>
Cc: Yang Shi <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

0 files changed, 0 insertions, 0 deletions