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rmap: support file thp

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Naive approach: on mapping/unmapping the page as compound we update
->_mapcount on each 4k page.  That's not efficient, but it's not obvious
how we can optimize this.  We can look into optimization later.

PG_double_map optimization doesn't work for file pages since lifecycle
of file pages is different comparing to anon pages: file page can be
mapped again at any time.

Link: http://lkml.kernel.org/r/1466021202-61880-11-git-send-email-kirill.shutemov@linux.intel.com
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Kirill A. Shutemov 2016-07-26 15:25:26 -07:00 • committed by Linus Torvalds
parent 7267ec008b
commit dd78fedde4
6 changed files with 52 additions and 20 deletions
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6
mm/util.c
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@ -412,6 +412,12 @@ int __page_mapcount(struct page *page)
int ret;
ret = atomic_read(&page->_mapcount) + 1;
/*
* For file THP page->_mapcount contains total number of mapping
* of the page: no need to look into compound_mapcount.
*/
if (!PageAnon(page) && !PageHuge(page))
return ret;
page = compound_head(page);
ret += atomic_read(compound_mapcount_ptr(page)) + 1;
if (PageDoubleMap(page))