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SubjectRe: [patch 2/3] mm: speculative get_page
Christoph Lameter wrote:
> Looks like the NoNewRefs flag is mostly ==
> spin_is_locked(mapping->tree_lock)? Would it not be better to check the
> tree_lock?
>

Well there are other uses for the tree_lock (eg. tag operations)
which do not need the "no new references" guarantee.

>
>
>>--- linux-2.6.orig/mm/migrate.c
>>+++ linux-2.6/mm/migrate.c
>>
>>+ SetPageNoNewRefs(page);
>> write_lock_irq(&mapping->tree_lock);
>
>
> A dream come true! If this is really working as it sounds then we can
> move the SetPageNoNewRefs up and avoid the final check under
> mapping->tree_lock. Then keep SetPageNoNewRefs until the page has been
> copied. It would basically play the same role as locking the page.
>

Yes we could do that but at this stage I wouldn't like to seperate
SetPageNoNewRefs from tree_lock, as it is replacing a traditional
guarantee that tree_lock no longer provides.

--
SUSE Labs, Novell Inc.
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