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authorKirill A. Shutemov <kirill.shutemov@linux.intel.com>2016-01-15 16:52:56 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2016-01-15 17:56:32 -0800
commitddc58f27f9eee9117219936f77e90ad5b2e00e96 (patch)
treea403f6b83ab95c297f6f6ab03a4756e2ea285d63 /mm/gup.c
parentad0bed24e98bcae9952c2d1f663ec7cb6344a387 (diff)
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mm: drop tail page refcounting
Tail page refcounting is utterly complicated and painful to support. It uses ->_mapcount on tail pages to store how many times this page is pinned. get_page() bumps ->_mapcount on tail page in addition to ->_count on head. This information is required by split_huge_page() to be able to distribute pins from head of compound page to tails during the split. We will need ->_mapcount to account PTE mappings of subpages of the compound page. We eliminate need in current meaning of ->_mapcount in tail pages by forbidding split entirely if the page is pinned. The only user of tail page refcounting is THP which is marked BROKEN for now. Let's drop all this mess. It makes get_page() and put_page() much simpler. Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Tested-by: Sasha Levin <sasha.levin@oracle.com> Tested-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Acked-by: Jerome Marchand <jmarchan@redhat.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Rik van Riel <riel@redhat.com> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Cc: Steve Capper <steve.capper@linaro.org> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Michal Hocko <mhocko@suse.cz> Cc: Christoph Lameter <cl@linux.com> Cc: David Rientjes <rientjes@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/gup.c')
-rw-r--r--mm/gup.c34
1 files changed, 4 insertions, 30 deletions
diff --git a/mm/gup.c b/mm/gup.c
index 1c50b506888d..7017abea9fd6 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -130,7 +130,7 @@ retry:
}
if (flags & FOLL_GET)
- get_page_foll(page);
+ get_page(page);
if (flags & FOLL_TOUCH) {
if ((flags & FOLL_WRITE) &&
!pte_dirty(pte) && !PageDirty(page))
@@ -1153,7 +1153,7 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
unsigned long end, int write, struct page **pages, int *nr)
{
- struct page *head, *page, *tail;
+ struct page *head, *page;
int refs;
if (write && !pmd_write(orig))
@@ -1162,7 +1162,6 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
refs = 0;
head = pmd_page(orig);
page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
- tail = page;
do {
VM_BUG_ON_PAGE(compound_head(page) != head, page);
pages[*nr] = page;
@@ -1183,24 +1182,13 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
return 0;
}
- /*
- * Any tail pages need their mapcount reference taken before we
- * return. (This allows the THP code to bump their ref count when
- * they are split into base pages).
- */
- while (refs--) {
- if (PageTail(tail))
- get_huge_page_tail(tail);
- tail++;
- }
-
return 1;
}
static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
unsigned long end, int write, struct page **pages, int *nr)
{
- struct page *head, *page, *tail;
+ struct page *head, *page;
int refs;
if (write && !pud_write(orig))
@@ -1209,7 +1197,6 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
refs = 0;
head = pud_page(orig);
page = head + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
- tail = page;
do {
VM_BUG_ON_PAGE(compound_head(page) != head, page);
pages[*nr] = page;
@@ -1230,12 +1217,6 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
return 0;
}
- while (refs--) {
- if (PageTail(tail))
- get_huge_page_tail(tail);
- tail++;
- }
-
return 1;
}
@@ -1244,7 +1225,7 @@ static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr,
struct page **pages, int *nr)
{
int refs;
- struct page *head, *page, *tail;
+ struct page *head, *page;
if (write && !pgd_write(orig))
return 0;
@@ -1252,7 +1233,6 @@ static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr,
refs = 0;
head = pgd_page(orig);
page = head + ((addr & ~PGDIR_MASK) >> PAGE_SHIFT);
- tail = page;
do {
VM_BUG_ON_PAGE(compound_head(page) != head, page);
pages[*nr] = page;
@@ -1273,12 +1253,6 @@ static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr,
return 0;
}
- while (refs--) {
- if (PageTail(tail))
- get_huge_page_tail(tail);
- tail++;
- }
-
return 1;
}