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    Subject[PATCH 06/11] mm: compaction: make isolate_lru_page() filter-aware again
    Date
    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@suse.de>
    ---
    include/linux/mmzone.h | 2 ++
    mm/compaction.c | 3 +++
    mm/vmscan.c | 35 +++++++++++++++++++++++++++++++++--
    3 files changed, 38 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 69057b5..16fb177 100644
    --- a/mm/vmscan.c
    +++ b/mm/vmscan.c
    @@ -1061,8 +1061,39 @@ 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
    + */
    + 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 pages without mappings or that have a
    + * ->migratepage callback are possible to migrate
    + * without blocking
    + */
    + mapping = page_mapping(page);
    + if (mapping && !mapping->a_ops->migratepage)
    + return ret;
    + }
    + }

    if ((mode & ISOLATE_UNMAPPED) && page_mapped(page))
    return ret;
    --
    1.7.3.4


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