Commit 9e16b7fb authored Feb 22, 2013 by Hugh Dickins Committed by Linus Torvalds Feb 23, 2013

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: Hugh 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: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus 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;
		}

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