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Commit 05759d38 authored by Andrea Arcangeli's avatar Andrea Arcangeli Committed by Linus Torvalds
Browse files

thp: split_huge_page anon_vma ordering dependency 



This documents how split_huge_page is safe vs new vma inserctions into the
anon_vma that may have already released the anon_vma->lock but not
established pmds yet when split_huge_page starts.

Signed-off-by: default avatarAndrea Arcangeli <aarcange@redhat.com>
Acked-by: default avatarMel Gorman <mel@csn.ul.ie>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 8a07651e

mm/huge_memory.c

+16 −0
Original line number Diff line number Diff line
@@ -841,6 +841,19 @@ static void __split_huge_page(struct page *page, 
			continue;

		mapcount += __split_huge_page_splitting(page, vma, addr);

	}

	/*

	 * It is critical that new vmas are added to the tail of the

	 * anon_vma list. This guarantes that if copy_huge_pmd() runs

	 * and establishes a child pmd before

	 * __split_huge_page_splitting() freezes the parent pmd (so if

	 * we fail to prevent copy_huge_pmd() from running until the

	 * whole __split_huge_page() is complete), we will still see

	 * the newly established pmd of the child later during the

	 * walk, to be able to set it as pmd_trans_splitting too.

	 */

	if (mapcount != page_mapcount(page))

		printk(KERN_ERR "mapcount %d page_mapcount %d\n",

		       mapcount, page_mapcount(page));

	BUG_ON(mapcount != page_mapcount(page));



	__split_huge_page_refcount(page);
@@ -854,6 +867,9 @@ static void __split_huge_page(struct page *page, 
			continue;

		mapcount2 += __split_huge_page_map(page, vma, addr);

	}

	if (mapcount != mapcount2)

		printk(KERN_ERR "mapcount %d mapcount2 %d page_mapcount %d\n",

		       mapcount, mapcount2, page_mapcount(page));

	BUG_ON(mapcount != mapcount2);

}

mm/rmap.c

+4 −0
Original line number Diff line number Diff line
@@ -177,6 +177,10 @@ static void anon_vma_chain_link(struct vm_area_struct *vma, 
	list_add(&avc->same_vma, &vma->anon_vma_chain);



	anon_vma_lock(anon_vma);

	/*

	 * It's critical to add new vmas to the tail of the anon_vma,

	 * see comment in huge_memory.c:__split_huge_page().

	 */

	list_add_tail(&avc->same_anon_vma, &anon_vma->head);

	anon_vma_unlock(anon_vma);

}