Commit 9e16b7fb authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds

mm,ksm: swapoff might need to copy

Before establishing that KSM page migration was the cause of my
WARN_ON_ONCE(page_mapped(page))s, I suspected that they came from the
lack of a ksm_might_need_to_copy() in swapoff's unuse_pte() - which in
many respects is equivalent to faulting in a page.

In fact I've never caught that as the cause: but in theory it does at
least need the KSM_RUN_UNMERGE check in ksm_might_need_to_copy(), to
avoid bringing a KSM page back in when it's not supposed to be.

I intended to copy how it's done in do_swap_page(), but have a strong
aversion to how "swapcache" ends up being used there: rework it with
"page != swapcache".
Signed-off-by: default avatarHugh Dickins <>
Cc: Mel Gorman <>
Cc: Petr Holasek <>
Cc: Andrea Arcangeli <>
Cc: Izik Eidus <>
Acked-by: default avatarJohannes Weiner <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent 5117b3b8
......@@ -874,11 +874,17 @@ unsigned int count_swap_pages(int type, int free)
static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
unsigned long addr, swp_entry_t entry, struct page *page)
struct page *swapcache;
struct mem_cgroup *memcg;
spinlock_t *ptl;
pte_t *pte;
int ret = 1;
swapcache = page;
page = ksm_might_need_to_copy(page, vma, addr);
if (unlikely(!page))
return -ENOMEM;
if (mem_cgroup_try_charge_swapin(vma->vm_mm, page,
GFP_KERNEL, &memcg)) {
ret = -ENOMEM;
......@@ -897,7 +903,10 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
set_pte_at(vma->vm_mm, addr, pte,
pte_mkold(mk_pte(page, vma->vm_page_prot)));
page_add_anon_rmap(page, vma, addr);
if (page == swapcache)
page_add_anon_rmap(page, vma, addr);
else /* ksm created a completely new copy */
page_add_new_anon_rmap(page, vma, addr);
mem_cgroup_commit_charge_swapin(page, memcg);
......@@ -908,6 +917,10 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
pte_unmap_unlock(pte, ptl);
if (page != swapcache) {
return ret;
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