mm: track the root (oldest) anon_vma (5c341ee1) · Commits · 戴 / test

Track the root (oldest) anon_vma in each anon_vma tree. Because we only take the lock on the root anon_vma, we cannot use the lock on higher-up anon_vmas to lock anything. This makes it impossible to do an indirect lookup of the root anon_vma, since the data structures could go away from under us. However, a direct pointer is safe because the root anon_vma is always the last one that gets freed on munmap or exit, by virtue of the same_vma list order and unlink_anon_vmas walking the list forward. [akpm@linux-foundation.org: fix typo] Signed-off-by:

Rik van Riel <riel@redhat.com> Acked-by:

Mel Gorman <mel@csn.ul.ie> Acked-by:

KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Tested-by:

Larry Woodman <lwoodman@redhat.com> Acked-by:

Larry Woodman <lwoodman@redhat.com> Reviewed-by:

Minchan Kim <minchan.kim@gmail.com> Acked-by:

Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

include/linux/rmap.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -26,6 +26,7 @@
		*/
		struct anon_vma {
		spinlock_t lock; /* Serialize access to vma list */
		struct anon_vma root; / Root of this anon_vma tree */
		#if defined(CONFIG_KSM) \|\| defined(CONFIG_MIGRATION)

		/*

mm/rmap.c

+16 −2

Original line number	Diff line number	Diff line
		@@ -132,6 +132,11 @@ int anon_vma_prepare(struct vm_area_struct *vma)
		if (unlikely(!anon_vma))
		goto out_enomem_free_avc;
		allocated = anon_vma;
		/*
		* This VMA had no anon_vma yet. This anon_vma is
		* the root of any anon_vma tree that might form.
		*/
		anon_vma->root = anon_vma;
		}

		anon_vma_lock(anon_vma);
		@@ -224,9 +229,15 @@ int anon_vma_fork(struct vm_area_struct vma, struct vm_area_struct pvma)
		avc = anon_vma_chain_alloc();
		if (!avc)
		goto out_error_free_anon_vma;
		anon_vma_chain_link(vma, avc, anon_vma);

		/*
		* The root anon_vma's spinlock is the lock actually used when we
		* lock any of the anon_vmas in this anon_vma tree.
		*/
		anon_vma->root = pvma->anon_vma->root;
		/* Mark this anon_vma as the one where our new (COWed) pages go. */
		vma->anon_vma = anon_vma;
		anon_vma_chain_link(vma, avc, anon_vma);

		return 0;

		@@ -261,7 +272,10 @@ void unlink_anon_vmas(struct vm_area_struct *vma)
		{
		struct anon_vma_chain avc, next;

		/* Unlink each anon_vma chained to the VMA. */
		/*
		* Unlink each anon_vma chained to the VMA. This list is ordered
		* from newest to oldest, ensuring the root anon_vma gets freed last.
		*/
		list_for_each_entry_safe(avc, next, &vma->anon_vma_chain, same_vma) {
		anon_vma_unlink(avc);
		list_del(&avc->same_vma);

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