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

Andrew Morton
2014-07-31T22:57:09Z

On Thu, 31 Jul 2014 11:22:35 +0900 Gioh Kim <gioh.kim@lge.com> 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@lge.com>
> Acked-by: Michal Nazarewicz <mina86@mina86.com>
> ---
> 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.