Commit ddc58f27 authored by Kirill A. Shutemov's avatar Kirill A. Shutemov Committed by Linus Torvalds
Browse files

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: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Tested-by: default avatarSasha Levin <sasha.levin@oracle.com>
Tested-by: default avatarAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
Acked-by: default avatarJerome 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent ad0bed24

arch/mips/mm/gup.c

+0 −4
Original line number Diff line number Diff line
@@ -87,8 +87,6 @@ static int gup_huge_pmd(pmd_t pmd, unsigned long addr, unsigned long end, 
	do {

		VM_BUG_ON(compound_head(page) != head);

		pages[*nr] = page;

		if (PageTail(page))

			get_huge_page_tail(page);

		(*nr)++;

		page++;

		refs++;
@@ -153,8 +151,6 @@ static int gup_huge_pud(pud_t pud, unsigned long addr, unsigned long end, 
	do {

		VM_BUG_ON(compound_head(page) != head);

		pages[*nr] = page;

		if (PageTail(page))

			get_huge_page_tail(page);

		(*nr)++;

		page++;

		refs++;

arch/powerpc/mm/hugetlbpage.c

+1 −12
Original line number Diff line number Diff line
@@ -999,7 +999,7 @@ int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr, 
{

	unsigned long mask;

	unsigned long pte_end;

	struct page *head, *page, *tail;

	struct page *head, *page;

	pte_t pte;

	int refs;
@@ -1022,7 +1022,6 @@ int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr, 
	head = pte_page(pte);



	page = head + ((addr & (sz-1)) >> PAGE_SHIFT);

	tail = page;

	do {

		VM_BUG_ON(compound_head(page) != head);

		pages[*nr] = page;
@@ -1044,15 +1043,5 @@ int gup_hugepte(pte_t *ptep, unsigned long sz, unsigned long addr, 
		return 0;

	}



	/*

	 * Any tail page need their mapcount reference taken before we

	 * return.

	 */

	while (refs--) {

		if (PageTail(tail))

			get_huge_page_tail(tail);

		tail++;

	}



	return 1;

}

arch/s390/mm/gup.c

+1 −12
Original line number Diff line number Diff line
@@ -55,7 +55,7 @@ static inline int gup_huge_pmd(pmd_t *pmdp, pmd_t pmd, unsigned long addr, 
		unsigned long end, int write, struct page **pages, int *nr)

{

	unsigned long mask, result;

	struct page *head, *page, *tail;

	struct page *head, *page;

	int refs;



	result = write ? 0 : _SEGMENT_ENTRY_PROTECT;
@@ -67,7 +67,6 @@ static inline int gup_huge_pmd(pmd_t *pmdp, pmd_t pmd, unsigned long addr, 
	refs = 0;

	head = pmd_page(pmd);

	page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);

	tail = page;

	do {

		VM_BUG_ON(compound_head(page) != head);

		pages[*nr] = page;
@@ -88,16 +87,6 @@ static inline int gup_huge_pmd(pmd_t *pmdp, pmd_t pmd, unsigned long addr, 
		return 0;

	}



	/*

	 * Any tail page need their mapcount reference taken before we

	 * return.

	 */

	while (refs--) {

		if (PageTail(tail))

			get_huge_page_tail(tail);

		tail++;

	}



	return 1;

}

arch/sparc/mm/gup.c

+1 −13
Original line number Diff line number Diff line
@@ -56,8 +56,6 @@ static noinline int gup_pte_range(pmd_t pmd, unsigned long addr, 
			put_page(head);

			return 0;

		}

		if (head != page)

			get_huge_page_tail(page);



		pages[*nr] = page;

		(*nr)++;
@@ -70,7 +68,7 @@ static int gup_huge_pmd(pmd_t *pmdp, pmd_t pmd, 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 (!(pmd_val(pmd) & _PAGE_VALID))
@@ -82,7 +80,6 @@ static int gup_huge_pmd(pmd_t *pmdp, pmd_t pmd, unsigned long addr, 
	refs = 0;

	head = pmd_page(pmd);

	page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);

	tail = page;

	do {

		VM_BUG_ON(compound_head(page) != head);

		pages[*nr] = page;
@@ -103,15 +100,6 @@ static int gup_huge_pmd(pmd_t *pmdp, pmd_t pmd, unsigned long addr, 
		return 0;

	}



	/* Any tail page need their mapcount reference taken before we

	 * return.

	 */

	while (refs--) {

		if (PageTail(tail))

			get_huge_page_tail(tail);

		tail++;

	}



	return 1;

}

arch/x86/mm/gup.c

+0 −4
Original line number Diff line number Diff line
@@ -136,8 +136,6 @@ static noinline int gup_huge_pmd(pmd_t pmd, unsigned long addr, 
	do {

		VM_BUG_ON_PAGE(compound_head(page) != head, page);

		pages[*nr] = page;

		if (PageTail(page))

			get_huge_page_tail(page);

		(*nr)++;

		page++;

		refs++;
@@ -212,8 +210,6 @@ static noinline int gup_huge_pud(pud_t pud, unsigned long addr, 
	do {

		VM_BUG_ON_PAGE(compound_head(page) != head, page);

		pages[*nr] = page;

		if (PageTail(page))

			get_huge_page_tail(page);

		(*nr)++;

		page++;

		refs++;

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