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ksm: enable KSM page migration

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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: Hugh 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Hugh Dickins 2013-02-22 16:35:13 -08:00 committed by Linus Torvalds
parent 4146d2d673
commit b79bc0a0c7
2 changed files with 4 additions and 20 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
mm/mempolicy.c
View File

@ -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))

21
mm/migrate.c
View File

@ -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 @@ uncharge:
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);