Re: [PATCH RESEND 2/2] mm/zswap: refoctor the get/put routines

From: Weijie Yang
Date: Sat Oct 26 2013 - 05:46:09 EST

On Fri, Oct 25, 2013 at 6:20 PM, Minchan Kim <minchan@xxxxxxxxxx> wrote:
> On Thu, Oct 24, 2013 at 05:53:32PM +0800, Weijie Yang wrote:
>> The refcount routine was not fit the kernel get/put semantic exactly,
>> There were too many judgement statements on refcount and it could be minus.
>> This patch does the following:
>> - move refcount judgement to zswap_entry_put() to hide resource free function.
>> - add a new function zswap_entry_find_get(), so that callers can use easily
>> in the following pattern:
>> zswap_entry_find_get
>> .../* do something */
>> zswap_entry_put
>> - to eliminate compile error, move some functions declaration
>> This patch is based on Minchan Kim <minchan@xxxxxxxxxx> 's idea and suggestion.
>> Signed-off-by: Weijie Yang <weijie.yang@xxxxxxxxxxx>
>> Cc: Seth Jennings <sjennings@xxxxxxxxxxxxxx>
>> Cc: Minchan Kim <minchan@xxxxxxxxxx>
>> Cc: Bob Liu <bob.liu@xxxxxxxxxx>
> I remember Bob had a idea to remove a look up and I think it's doable.
> Anyway, I don't mind you send it with fix or not.

Thanks for review.

Bob's idea is:
"Then how about use if (!RB_EMPTY_NODE(&entry->rbnode)) to
replace rbtree searching?"

I'm afraid not. Because entry could be freed in previous zswap_entry_put,
we cann't reference entry or we would touch a free-and-use issue.

> Thanks for handling this, Weijie!
> Acked-by: Minchan Kim <minchan@xxxxxxxxxx>
> --
> Kind regards,
> Minchan Kim
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