On Fri, 04 Jul 2014 17:25:09 +0900 Gioh Kim <gioh.kim@xxxxxxx> wrote:
> From: Gioh Kim <gioh.kim@xxxxxxx>
> Date: Fri, 4 Jul 2014 16:53:22 +0900
> Subject: [PATCH] [RFC] CMA: clear buffer-head lru before page migration
>
> When CMA try to migrate page, some buffer-heads can exist on lru.
> The bh on lru has non-zero count value so that it cannot be dropped
> even-if it is not used. We can drop only buffers related to the
> migrated page, but it can take long time more than dropping all
> because of searching list. There all buffers in lru are dropped.
>
> Signed-off-by: Laura Abbott <lauraa@xxxxxxxxxxxxxx>
> Signed-off-by: Gioh Kim <gioh.kim@xxxxxxx>
> ---
> fs/buffer.c | 13 +++++++++++++
> 1 file changed, 13 insertions(+)
>
> diff --git a/fs/buffer.c b/fs/buffer.c
> index eba6e4f..4f11b7a 100644
> --- a/fs/buffer.c
> +++ b/fs/buffer.c
> @@ -3233,6 +3233,19 @@ int try_to_free_buffers(struct page *page)
> if (PageWriteback(page))
> return 0;
>
> +#ifdef CONFIG_CMA
> + /*
> + * When CMA try to migrate page, some buffer-heads can exist on lru.
> + * The bh on lru has non-zero count value so that it cannot
> + * be dropped even-if it is not used.
> + * We can drop only buffers related to the migrated page,
> + * but it can take long time more than dropping all
> + * because of searching list.
> + * There all buffers in lru are dropped first.
> + */
> + invalidate_bh_lrus();
> +#endif
No, this will be tremendously expensive.
What I proposed is that CMA call invalidate_bh_lrus() right at the
outset. Something along the lines of
--- a/mm/page_alloc.c~a
+++ a/mm/page_alloc.c
@@ -6329,6 +6329,14 @@ int alloc_contig_range(unsigned long sta
};
INIT_LIST_HEAD(&cc.migratepages);
+#ifdef CONFIG_CMA
+ /*
+ * Comment goes here
+ */
+ if (migratetype == MIGRATE_CMA)
+ invalidate_bh_lrus();
+#endif
+
/*
* What we do here is we mark all pageblocks in range as
* MIGRATE_ISOLATE. Because pageblock and max order pages may
- I'd have thought that it would make sense to do this for huge pages
as well (MIGRATE_MOVABLE) but nobody really seems to know.
- There's a patch floating around ("Allow increasing the buffer-head
per-CPU LRU size") which will double the size of the bh lrus, so this
all becomes more important.
- alloc_contig_range() does lru_add_drain_all() and drain_all_pages()
*after* performing the allocation. I can't work out why this is the
case and of course it is undocumented. If this is indeed not a bug
then probably the invalidate_bh_lrus() should happen in the same
place.
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