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Commit b79bc0a0 authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
Browse files

ksm: enable KSM page migration 



Migration of KSM pages is now safe: remove the PageKsm restrictions from
mempolicy.c and migrate.c.

But keep PageKsm out of __unmap_and_move()'s anon_vma contortions, which
are irrelevant to KSM: it looks as if that code was preventing hotremove
migration of KSM pages, unless they happened to be in swapcache.

There is some question as to whether enforcing a NUMA mempolicy migration
ought to migrate KSM pages, mapped into entirely unrelated processes; but
moving page_mapcount > 1 is only permitted with MPOL_MF_MOVE_ALL anyway,
and it seems reasonable to assume that you wouldn't set MADV_MERGEABLE on
any area where this is a worry.

Signed-off-by: default avatarHugh Dickins <hughd@google.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Petr Holasek <pholasek@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Izik Eidus <izik.eidus@ravellosystems.com>
Cc: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 4146d2d6

mm/mempolicy.c

+1 −2
Original line number Diff line number Diff line
@@ -496,9 +496,8 @@ static int check_pte_range(struct vm_area_struct *vma, pmd_t *pmd, 
		/*

		 * vm_normal_page() filters out zero pages, but there might

		 * still be PageReserved pages to skip, perhaps in a VDSO.

		 * And we cannot move PageKsm pages sensibly or safely yet.

		 */

		if (PageReserved(page) || PageKsm(page))

		if (PageReserved(page))

			continue;

		nid = page_to_nid(page);

		if (node_isset(nid, *nodes) == !!(flags & MPOL_MF_INVERT))

mm/migrate.c

+3 −18
Original line number Diff line number Diff line
@@ -731,20 +731,6 @@ static int __unmap_and_move(struct page *page, struct page *newpage, 
		lock_page(page);

	}



	/*

	 * Only memory hotplug's offline_pages() caller has locked out KSM,

	 * and can safely migrate a KSM page.  The other cases have skipped

	 * PageKsm along with PageReserved - but it is only now when we have

	 * the page lock that we can be certain it will not go KSM beneath us

	 * (KSM will not upgrade a page from PageAnon to PageKsm when it sees

	 * its pagecount raised, but only here do we take the page lock which

	 * serializes that).

	 */

	if (PageKsm(page) && !offlining) {

		rc = -EBUSY;

		goto unlock;

	}



	/* charge against new page */

	mem_cgroup_prepare_migration(page, newpage, &mem);
@@ -771,7 +757,7 @@ static int __unmap_and_move(struct page *page, struct page *newpage, 
	 * File Caches may use write_page() or lock_page() in migration, then,

	 * just care Anon page here.

	 */

	if (PageAnon(page)) {

	if (PageAnon(page) && !PageKsm(page)) {

		/*

		 * Only page_lock_anon_vma_read() understands the subtleties of

		 * getting a hold on an anon_vma from outside one of its mms.
@@ -851,7 +837,6 @@ static int __unmap_and_move(struct page *page, struct page *newpage, 
	mem_cgroup_end_migration(mem, page, newpage,

				 (rc == MIGRATEPAGE_SUCCESS ||

				  rc == MIGRATEPAGE_BALLOON_SUCCESS));

unlock:

	unlock_page(page);

out:

	return rc;
@@ -1155,7 +1140,7 @@ static int do_move_page_to_node_array(struct mm_struct *mm, 
			goto set_status;



		/* Use PageReserved to check for zero page */

		if (PageReserved(page) || PageKsm(page))

		if (PageReserved(page))

			goto put_and_set;



		pp->page = page;
@@ -1317,7 +1302,7 @@ static void do_pages_stat_array(struct mm_struct *mm, unsigned long nr_pages, 


		err = -ENOENT;

		/* Use PageReserved to check for zero page */

		if (!page || PageReserved(page) || PageKsm(page))

		if (!page || PageReserved(page))

			goto set_status;



		err = page_to_nid(page);