On Mon, Nov 21, 2011 at 06:36:46PM +0000, Mel Gorman wrote:
> Commit [39deaf85: mm: compaction: make isolate_lru_page() filter-aware]
> noted that compaction does not migrate dirty or writeback pages and
> that is was meaningless to pick the page and re-add it to the LRU list.
> This had to be partially reverted because some dirty pages can be
> migrated by compaction without blocking.
>
> This patch updates "mm: compaction: make isolate_lru_page" by skipping
> over pages that migration has no possibility of migrating to minimise
> LRU disruption.
>
> Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
> ---
> include/linux/mmzone.h | 2 ++
> mm/compaction.c | 3 +++
> mm/vmscan.c | 36 ++++++++++++++++++++++++++++++++++--
> 3 files changed, 39 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index 188cb2f..ac5b522 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -173,6 +173,8 @@ static inline int is_unevictable_lru(enum lru_list l)
> #define ISOLATE_CLEAN ((__force isolate_mode_t)0x4)
> /* Isolate unmapped file */
> #define ISOLATE_UNMAPPED ((__force isolate_mode_t)0x8)
> +/* Isolate for asynchronous migration */
> +#define ISOLATE_ASYNC_MIGRATE ((__force isolate_mode_t)0x10)
>
> /* LRU Isolation modes. */
> typedef unsigned __bitwise__ isolate_mode_t;
> diff --git a/mm/compaction.c b/mm/compaction.c
> index 615502b..0379263 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -349,6 +349,9 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
> continue;
> }
>
> + if (!cc->sync)
> + mode |= ISOLATE_ASYNC_MIGRATE;
> +
> /* Try isolate the page */
> if (__isolate_lru_page(page, mode, 0) != 0)
> continue;
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index 3421746..28df0ed 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -1061,8 +1061,40 @@ int __isolate_lru_page(struct page *page, isolate_mode_t mode, int file)
>
> ret = -EBUSY;
>
> - if ((mode & ISOLATE_CLEAN) && (PageDirty(page) || PageWriteback(page)))
> - return ret;
> + /*
> + * To minimise LRU disruption, the caller can indicate that it only
> + * wants to isolate pages it will be able to operate on without
> + * blocking - clean pages for the most part.
> + *
> + * ISOLATE_CLEAN means that only clean pages should be isolated. This
> + * is used by reclaim when it is cannot write to backing storage
> + *
> + * ISOLATE_ASYNC_MIGRATE is used to indicate that it only wants to pages
> + * that it is possible to migrate without blocking with a ->migratepage
> + * handler
> + */
> + if (mode & (ISOLATE_CLEAN|ISOLATE_ASYNC_MIGRATE)) {
> + /* All the caller can do on PageWriteback is block */
> + if (PageWriteback(page))
> + return ret;
> +
> + if (PageDirty(page)) {
> + struct address_space *mapping;
> +
> + /* ISOLATE_CLEAN means only clean pages */
> + if (mode & ISOLATE_CLEAN)
> + return ret;
> +
> + /*
> + * Only the ->migratepage callback knows if a dirty
> + * page can be migrated without blocking. Skip the
> + * page unless there is a ->migratepage callback.
> + */
> + mapping = page_mapping(page);
> + if (!mapping || !mapping->a_ops->migratepage)
I didn't review 4/7 carefully yet.
In case of page_mapping is NULL, move_to_new_page calls migrate_page
which is non-blocking function. So, I guess it could be migrated without blocking.
--
Kind regards,
Minchan Kim
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