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mm: drop tail page refcounting

Browse source 
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 <[email protected]>
Tested-by: Sasha Levin <[email protected]>
Tested-by: Aneesh Kumar K.V <[email protected]>
Acked-by: Vlastimil Babka <[email protected]>
Acked-by: Jerome Marchand <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Naoya Horiguchi <[email protected]>
Cc: Steve Capper <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: David Rientjes <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Kirill A. Shutemov 2016-01-15 16:52:56 -08:00 • committed by Linus Torvalds
commit ddc58f27f9
12 changed files with 40 additions and 466 deletions
Download patch file Download diff file Expand all files Collapse all files

34
mm/gup.c
View file

@ -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;
}