memcg, THP, swap: avoid to duplicated charge THP in swap cache

For a THP (Transparent Huge Page), tail_page->mem_cgroup is NULL.  So to
check whether the page is charged already, we need to check the head
page.  This is not an issue before because it is impossible for a THP to
be in the swap cache before.  But after we add delaying splitting THP
after swapped out support, it is possible now.

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: "Huang, Ying" <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: "Kirill A . Shutemov" <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Ross Zwisler <[email protected]> [for brd.c, zram_drv.c, pmem.c]
Cc: Shaohua Li <[email protected]>
Cc: Vishal L Verma <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions