linux-kernel - Re: unused swap offset / bad page map.

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Date:	Thu, 22 Aug 2013 11:21:28 +0800
From:	Hillf Danton <dhillf@...il.com>
To:	Dave Jones <davej@...hat.com>, Hillf Danton <dhillf@...il.com>,
	Linux-MM <linux-mm@...ck.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: unused swap offset / bad page map.

On Thu, Aug 22, 2013 at 4:49 AM, Dave Jones <davej@...hat.com> wrote:
>
> didn't hit the bug_on, but got a bunch of
>
> [  424.077993] swap_free: Unused swap offset entry 000187d5
> [  439.377194] swap_free: Unused swap offset entry 000187e7
> [  441.998411] swap_free: Unused swap offset entry 000187ee
> [  446.956551] swap_free: Unused swap offset entry 0000245f
>
If page is reused, its swap entry is freed.

reuse_swap_page()
  delete_from_swap_cache()
    swapcache_free()
      count = swap_entry_free(p, entry, SWAP_HAS_CACHE);

If count drops to zero, then swap_free() gives warning.


--- a/mm/memory.c Wed Aug  7 16:29:34 2013
+++ b/mm/memory.c Thu Aug 22 10:44:32 2013
@@ -3123,6 +3123,7 @@ static int do_swap_page(struct mm_struct
  /* It's better to call commit-charge after rmap is established */
  mem_cgroup_commit_charge_swapin(page, ptr);

+ if (!exclusive)
  swap_free(entry);
  if (vm_swap_full() || (vma->vm_flags & VM_LOCKED) || PageMlocked(page))
  try_to_free_swap(page);
--
--
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