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    Subject[PATCH 02/15] mm: compaction: introduce isolate_migratepages_range().
    From: Michal Nazarewicz <mina86@mina86.com>

    This commit introduces isolate_migratepages_range() function which
    extracts functionality from isolate_migratepages() so that it can be
    used on arbitrary PFN ranges.

    isolate_migratepages() function is implemented as a simple wrapper
    around isolate_migratepages_range().

    Signed-off-by: Michal Nazarewicz <mina86@mina86.com>
    Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
    Acked-by: Mel Gorman <mel@csn.ul.ie>
    Tested-by: Rob Clark <rob.clark@linaro.org>
    Tested-by: Ohad Ben-Cohen <ohad@wizery.com>
    Tested-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
    ---
    mm/compaction.c | 75 +++++++++++++++++++++++++++++++++++++++---------------
    1 files changed, 54 insertions(+), 21 deletions(-)

    diff --git a/mm/compaction.c b/mm/compaction.c
    index 71a58f6..62902b6 100644
    --- a/mm/compaction.c
    +++ b/mm/compaction.c
    @@ -250,31 +250,34 @@ typedef enum {
    ISOLATE_SUCCESS, /* Pages isolated, migrate */
    } isolate_migrate_t;

    -/*
    - * Isolate all pages that can be migrated from the block pointed to by
    - * the migrate scanner within compact_control.
    +/**
    + * isolate_migratepages_range() - isolate all migrate-able pages in range.
    + * @zone: Zone pages are in.
    + * @cc: Compaction control structure.
    + * @low_pfn: The first PFN of the range.
    + * @end_pfn: The one-past-the-last PFN of the range.
    + *
    + * Isolate all pages that can be migrated from the range specified by
    + * [low_pfn, end_pfn). Returns zero if there is a fatal signal
    + * pending), otherwise PFN of the first page that was not scanned
    + * (which may be both less, equal to or more then end_pfn).
    + *
    + * Assumes that cc->migratepages is empty and cc->nr_migratepages is
    + * zero.
    + *
    + * Apart from cc->migratepages and cc->nr_migratetypes this function
    + * does not modify any cc's fields, in particular it does not modify
    + * (or read for that matter) cc->migrate_pfn.
    */
    -static isolate_migrate_t isolate_migratepages(struct zone *zone,
    - struct compact_control *cc)
    +static unsigned long
    +isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
    + unsigned long low_pfn, unsigned long end_pfn)
    {
    - unsigned long low_pfn, end_pfn;
    unsigned long last_pageblock_nr = 0, pageblock_nr;
    unsigned long nr_scanned = 0, nr_isolated = 0;
    struct list_head *migratelist = &cc->migratepages;
    isolate_mode_t mode = ISOLATE_ACTIVE|ISOLATE_INACTIVE;

    - /* Do not scan outside zone boundaries */
    - low_pfn = max(cc->migrate_pfn, zone->zone_start_pfn);
    -
    - /* Only scan within a pageblock boundary */
    - end_pfn = ALIGN(low_pfn + pageblock_nr_pages, pageblock_nr_pages);
    -
    - /* Do not cross the free scanner or scan within a memory hole */
    - if (end_pfn > cc->free_pfn || !pfn_valid(low_pfn)) {
    - cc->migrate_pfn = end_pfn;
    - return ISOLATE_NONE;
    - }
    -
    /*
    * Ensure that there are not too many pages isolated from the LRU
    * list by either parallel reclaimers or compaction. If there are,
    @@ -283,12 +286,12 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
    while (unlikely(too_many_isolated(zone))) {
    /* async migration should just abort */
    if (!cc->sync)
    - return ISOLATE_ABORT;
    + return 0;

    congestion_wait(BLK_RW_ASYNC, HZ/10);

    if (fatal_signal_pending(current))
    - return ISOLATE_ABORT;
    + return 0;
    }

    /* Time to isolate some pages for migration */
    @@ -374,10 +377,40 @@ static isolate_migrate_t isolate_migratepages(struct zone *zone,
    acct_isolated(zone, cc);

    spin_unlock_irq(&zone->lru_lock);
    - cc->migrate_pfn = low_pfn;

    trace_mm_compaction_isolate_migratepages(nr_scanned, nr_isolated);

    + return low_pfn;
    +}
    +
    +/*
    + * Isolate all pages that can be migrated from the block pointed to by
    + * the migrate scanner within compact_control.
    + */
    +static isolate_migrate_t isolate_migratepages(struct zone *zone,
    + struct compact_control *cc)
    +{
    + unsigned long low_pfn, end_pfn;
    +
    + /* Do not scan outside zone boundaries */
    + low_pfn = max(cc->migrate_pfn, zone->zone_start_pfn);
    +
    + /* Only scan within a pageblock boundary */
    + end_pfn = ALIGN(low_pfn + pageblock_nr_pages, pageblock_nr_pages);
    +
    + /* Do not cross the free scanner or scan within a memory hole */
    + if (end_pfn > cc->free_pfn || !pfn_valid(low_pfn)) {
    + cc->migrate_pfn = end_pfn;
    + return ISOLATE_NONE;
    + }
    +
    + /* Perform the isolation */
    + low_pfn = isolate_migratepages_range(zone, cc, low_pfn, end_pfn);
    + if (!low_pfn)
    + return ISOLATE_ABORT;
    +
    + cc->migrate_pfn = low_pfn;
    +
    return ISOLATE_SUCCESS;
    }

    --
    1.7.1.569.g6f426


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