Re: [PATCH 08/10] mm/page_alloc: use get_onbuddy_migratetype() to get buddy list type

[Vlastimil Babka]

On 07/08/2014 03:01 AM, Gioh Kim wrote:
> 2014-07-08 ìì 12:57, Vlastimil Babka ì ê:
> > On 07/04/2014 09:57 AM, Joonsoo Kim wrote:
> > > When isolating free page, what we want to know is which list
> > > the page is linked. If it is linked in isolate migratetype buddy list,
> > > we can skip watermark check and freepage counting. And if it is linked
> > > in CMA migratetype buddy list, we need to fixup freepage counting. For
> > > this purpose, get_onbuddy_migratetype() is more fit and cheap than
> > > get_pageblock_migratetype(). So use it.
> >
> > Hm but you made get_onbuddy_migratetype() work only with CONFIG_MEMORY_ISOLATION. And __isolate_free_page is (despite the name) not at all limited to CONFIG_MEMORY_ISOLATION.
>
> Current __isolate_free_page is called by only split_free_page, and split_free_page by isolate_freepages_block.
> split_free_page is called only for isolated pages now but It can be changed someday.

Yeah, but isolate_freepages_block is also not part of 
CONFIG_MEMORY_ISOLATION. Unfortunately, there are two distinct concepts 
of memory isolation and LRU isolation, that are not distinguished in 
function names.

> I think get_onbuddy_migratetype should work with any situation.
>
> And I think the name of get_onbuddy_migratetype is confused.
> Because of _onbuddy_, it might look like that the pages are buddy pages.
> I think the original name _freepage_ is proper one.
>
>
> > > Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> > > ---
> > >    mm/page_alloc.c |    2 +-
> > >    1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > > index e1c4c3e..d9fb8bb 100644
> > > --- a/mm/page_alloc.c
> > > +++ b/mm/page_alloc.c
> > > @@ -1597,7 +1597,7 @@ static int __isolate_free_page(struct page *page, unsigned int order)
> > >        BUG_ON(!PageBuddy(page));
> > >
> > >        zone = page_zone(page);
> > > -    mt = get_pageblock_migratetype(page);
> > > +    mt = get_onbuddy_migratetype(page);
> > >
> > >        if (!is_migrate_isolate(mt)) {
> > >            /* Obey watermarks as if the page was being allocated */
>
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