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

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 <hughd@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Petr Holasek <pholasek@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Izik Eidus <izik.eidus@ravellosystems.com>
Acked-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 5117b3b8

mm/swapfile.c

+14 −1
Original line number Diff line number Diff line
@@ -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, 
	get_page(page);

	set_pte_at(vma->vm_mm, addr, pte,

		   pte_mkold(mk_pte(page, vma->vm_page_prot)));

	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);

	swap_free(entry);

	/*
@@ -908,6 +917,10 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd, 
out:

	pte_unmap_unlock(pte, ptl);

out_nolock:

	if (page != swapcache) {

		unlock_page(page);

		put_page(page);

	}

	return ret;

}