* [RFC patch] vm: clear swap entry before copying pte
@ 2012-07-27 13:53 Hillf Danton
2012-07-31 2:34 ` Hugh Dickins
0 siblings, 1 reply; 3+ messages in thread
From: Hillf Danton @ 2012-07-27 13:53 UTC (permalink / raw)
To: Hugh Dickins; +Cc: KOSAKI Motohiro, Mel Gorman, Andrew Morton, LKML, Linux-MM
If swap entry is cleared, we can see the reason that copying pte is
interrupted. If due to page table lock held long enough, no need to
increase swap count.
Signed-off-by: Hillf Danton <dhillf@gmail.com>
---
--- a/mm/memory.c Fri Jul 27 21:33:32 2012
+++ b/mm/memory.c Fri Jul 27 21:35:24 2012
@@ -971,6 +971,7 @@ again:
if (add_swap_count_continuation(entry, GFP_KERNEL) < 0)
return -ENOMEM;
progress = 0;
+ entry.val = 0;
}
if (addr != end)
goto again;
--
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^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [RFC patch] vm: clear swap entry before copying pte
2012-07-27 13:53 [RFC patch] vm: clear swap entry before copying pte Hillf Danton
@ 2012-07-31 2:34 ` Hugh Dickins
2012-07-31 12:32 ` Hillf Danton
0 siblings, 1 reply; 3+ messages in thread
From: Hugh Dickins @ 2012-07-31 2:34 UTC (permalink / raw)
To: Hillf Danton; +Cc: KOSAKI Motohiro, Mel Gorman, Andrew Morton, LKML, Linux-MM
On Fri, 27 Jul 2012, Hillf Danton wrote:
>
> If swap entry is cleared, we can see the reason that copying pte is
> interrupted. If due to page table lock held long enough, no need to
> increase swap count.
I can't see a bug to be fixed here.
How would it break out of the loop above without freshly setting entry
(given that mmap_sem is held with down_write, so the entries cannot be
munmap'ped by another thread)? How would it matter if it could (given
that add_swap_count_continuation already allows for races; and if there
were a problem, the call just made could be equally at fault)?
Nor do I understand your description.
But I can see that the lack of reinitialization of entry.val here
does raise doubt and confusion. A better tidyup would be to remove
the initialization of swp_entry_t entry from its onstack declaration,
and do it at the again label instead.
If you send a patch to do that instead, I could probably ack it -
but expect I shall want to change your description.
Hugh
>
> Signed-off-by: Hillf Danton <dhillf@gmail.com>
> ---
>
> --- a/mm/memory.c Fri Jul 27 21:33:32 2012
> +++ b/mm/memory.c Fri Jul 27 21:35:24 2012
> @@ -971,6 +971,7 @@ again:
> if (add_swap_count_continuation(entry, GFP_KERNEL) < 0)
> return -ENOMEM;
> progress = 0;
> + entry.val = 0;
> }
> if (addr != end)
> goto again;
> --
--
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^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [RFC patch] vm: clear swap entry before copying pte
2012-07-31 2:34 ` Hugh Dickins
@ 2012-07-31 12:32 ` Hillf Danton
0 siblings, 0 replies; 3+ messages in thread
From: Hillf Danton @ 2012-07-31 12:32 UTC (permalink / raw)
To: Hugh Dickins; +Cc: KOSAKI Motohiro, Mel Gorman, Andrew Morton, LKML, Linux-MM
Hi Hugh,
On Tue, Jul 31, 2012 at 10:34 AM, Hugh Dickins <hughd@google.com> wrote:
> But I can see that the lack of reinitialization of entry.val here
> does raise doubt and confusion. A better tidyup would be to remove
> the initialization of swp_entry_t entry from its onstack declaration,
> and do it at the again label instead.
I just want to avoid allocating page in add_swap_count_continuation()
for non clear reason, as you see, which is not a bug fix.
Thanks,
Hillf
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^ permalink raw reply [flat|nested] 3+ messages in thread
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2012-07-27 13:53 [RFC patch] vm: clear swap entry before copying pte Hillf Danton
2012-07-31 2:34 ` Hugh Dickins
2012-07-31 12:32 ` Hillf Danton
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