Re: [PATCHv2] CMA/HOTPLUG: clear buffer-head lru before page migration

[Gioh Kim]

2014-08-01 ìì 7:57, Andrew Morton ì ê:
> On Thu, 31 Jul 2014 11:22:35 +0900 Gioh Kim <gioh.kim@xxxxxxx> wrote:
>
> > The previous PATCH inserts invalidate_bh_lrus() only into CMA code.
> > HOTPLUG needs also dropping bh of lru.
> > So v2 inserts invalidate_bh_lrus() into both of CMA and HOTPLUG.
> >
> >
> > ---------------------------- 8< ----------------------------
> > The bh must be free to migrate a page at which bh is mapped.
> > The reference count of bh is increased when it is installed
> > into lru so that the bh of lru must be freed before migrating the page.
> >
> > This frees every bh of lru. We could free only bh of migrating page.
> > But searching lru sometimes costs more than invalidating entire lru.
> >
> > Signed-off-by: Gioh Kim <gioh.kim@xxxxxxx>
> > Acked-by: Michal Nazarewicz <mina86@xxxxxxxxxx>
> > ---
> >   mm/memory_hotplug.c |    1 +
> >   mm/page_alloc.c     |    2 ++
> >   2 files changed, 3 insertions(+)
> >
> > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> > index a3797d3..1c5454f 100644
> > --- a/mm/memory_hotplug.c
> > +++ b/mm/memory_hotplug.c
> > @@ -1672,6 +1672,7 @@ repeat:
> >                  lru_add_drain_all();
> >                  cond_resched();
> >                  drain_all_pages();
> > +               invalidate_bh_lrus();
>
> Both of these calls should have a comment explaining why
> invalidate_bh_lrus() is being called.
>
> >          }
> >
> >          pfn = scan_movable_pages(start_pfn, end_pfn);
> > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > index b99643d4..c00dedf 100644
> > --- a/mm/page_alloc.c
> > +++ b/mm/page_alloc.c
> > @@ -6369,6 +6369,8 @@ int alloc_contig_range(unsigned long start, unsigned long end,
> >          if (ret)
> >                  return ret;
> >
> > +       invalidate_bh_lrus();
> > +
> >          ret = __alloc_contig_migrate_range(&cc, start, end);
> >          if (ret)
> >                  goto done;
>
> I do feel that this change is likely to be beneficial, but I don't want
> to apply such a patch until I know what its effects are upon all
> alloc_contig_range() callers.  Especially hugetlb.

I'm very sorry to hear that.
How can I check the effects?


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