Commit e317a8d8 authored by David Hildenbrand's avatar David Hildenbrand Committed by Andrew Morton
Browse files

mm/ksm: convert break_ksm() from walk_page_range_vma() to folio_walk 

Let's simplify by reusing folio_walk.  Keep the existing behavior by
handling migration entries and zeropages.

Link: https://lkml.kernel.org/r/20240802155524.517137-12-david@redhat.com


Signed-off-by: default avatarDavid Hildenbrand <david@redhat.com>
Cc: Alexander Gordeev <agordeev@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@linux.ibm.com>
Cc: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Janosch Frank <frankja@linux.ibm.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Sven Schnelle <svens@linux.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 7290840d

mm/ksm.c

+16 −47
Original line number Diff line number Diff line
@@ -608,47 +608,6 @@ static inline bool ksm_test_exit(struct mm_struct *mm) 
	return atomic_read(&mm->mm_users) == 0;

}



static int break_ksm_pmd_entry(pmd_t *pmd, unsigned long addr, unsigned long next,

			struct mm_walk *walk)

{

	struct page *page = NULL;

	spinlock_t *ptl;

	pte_t *pte;

	pte_t ptent;

	int ret;



	pte = pte_offset_map_lock(walk->mm, pmd, addr, &ptl);

	if (!pte)

		return 0;

	ptent = ptep_get(pte);

	if (pte_present(ptent)) {

		page = vm_normal_page(walk->vma, addr, ptent);

	} else if (!pte_none(ptent)) {

		swp_entry_t entry = pte_to_swp_entry(ptent);



		/*

		 * As KSM pages remain KSM pages until freed, no need to wait

		 * here for migration to end.

		 */

		if (is_migration_entry(entry))

			page = pfn_swap_entry_to_page(entry);

	}

	/* return 1 if the page is an normal ksm page or KSM-placed zero page */

	ret = (page && PageKsm(page)) || is_ksm_zero_pte(ptent);

	pte_unmap_unlock(pte, ptl);

	return ret;

}



static const struct mm_walk_ops break_ksm_ops = {

	.pmd_entry = break_ksm_pmd_entry,

	.walk_lock = PGWALK_RDLOCK,

};



static const struct mm_walk_ops break_ksm_lock_vma_ops = {

	.pmd_entry = break_ksm_pmd_entry,

	.walk_lock = PGWALK_WRLOCK,

};



/*

 * We use break_ksm to break COW on a ksm page by triggering unsharing,

 * such that the ksm page will get replaced by an exclusive anonymous page.
@@ -665,16 +624,26 @@ static const struct mm_walk_ops break_ksm_lock_vma_ops = { 
static int break_ksm(struct vm_area_struct *vma, unsigned long addr, bool lock_vma)

{

	vm_fault_t ret = 0;

	const struct mm_walk_ops *ops = lock_vma ?

				&break_ksm_lock_vma_ops : &break_ksm_ops;



	if (lock_vma)

		vma_start_write(vma);



	do {

		int ksm_page;

		bool ksm_page = false;

		struct folio_walk fw;

		struct folio *folio;



		cond_resched();

		ksm_page = walk_page_range_vma(vma, addr, addr + 1, ops, NULL);

		if (WARN_ON_ONCE(ksm_page < 0))

			return ksm_page;

		folio = folio_walk_start(&fw, vma, addr,

					 FW_MIGRATION | FW_ZEROPAGE);

		if (folio) {

			/* Small folio implies FW_LEVEL_PTE. */

			if (!folio_test_large(folio) &&

			    (folio_test_ksm(folio) || is_ksm_zero_pte(fw.pte)))

				ksm_page = true;

			folio_walk_end(&fw, vma);

		}



		if (!ksm_page)

			return 0;

		ret = handle_mm_fault(vma, addr,