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SubjectRe: [PATCH 5/11] ksm: get_ksm_page locked
On Thu, Feb 07, 2013 at 04:33:58PM -0800, Hugh Dickins wrote:
> > > <SNIP>
> > > --- mmotm.orig/mm/ksm.c 2013-01-25 14:36:53.244205966 -0800
> > > +++ mmotm/mm/ksm.c 2013-01-25 14:36:58.856206099 -0800
> > > @@ -514,15 +514,14 @@ static void remove_node_from_stable_tree
> > > * but this is different - made simpler by ksm_thread_mutex being held, but
> > > * interesting for assuming that no other use of the struct page could ever
> > > * put our expected_mapping into page->mapping (or a field of the union which
> > > - * coincides with page->mapping). The RCU calls are not for KSM at all, but
> > > - * to keep the page_count protocol described with page_cache_get_speculative.
> > > + * coincides with page->mapping).
> > > *
> > > * Note: it is possible that get_ksm_page() will return NULL one moment,
> > > * then page the next, if the page is in between page_freeze_refs() and
> > > * page_unfreeze_refs(): this shouldn't be a problem anywhere, the page
> > > * is on its way to being freed; but it is an anomaly to bear in mind.
> > > */
> > > -static struct page *get_ksm_page(struct stable_node *stable_node)
> > > +static struct page *get_ksm_page(struct stable_node *stable_node, bool locked)
> > > {
> >
> > The naming is unhelpful :(
> >
> > Because the second parameter is called "locked", it implies that the
> > caller of this function holds the page lock (which is obviously very
> > silly). ret_locked maybe?
>
> I'd prefer "lock_it": I'll make that change unless you've a better.
>

I don't.

> >
> > As the function is akin to find_lock_page I would prefer if there was
> > a new get_lock_ksm_page() instead of locking depending on the value of a
> > parameter.
>
> I demur. If it were a global interface rather than a function static
> to ksm.c, yes, I'm sure Linus would side very strongly with you, and I'd
> be providing a pair of wrappers to get_ksm_page() to hide the bool arg.
>
> But this is a private function (you're invited :) which doesn't need
> that level of hand-holding.
>
> And I'm a firm believer in having one, difficult, function where all
> the heavy thought is focussed, which does the nasty work and spares
> everywhere else from having to worry about the difficulties.
>

Ok, I'm convinced. As you say, the case for having one function is a lot
strong later in the series when this function becomes quite complex. Thanks.

--
Mel Gorman
SUSE Labs


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