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    Subject[PATCH 06/27] mm, vmscan: Begin reclaiming pages on a per-node basis
    Date
    This patch makes reclaim decisions on a per-node basis. A reclaimer knows
    what zone is required by the allocation request and skips pages from
    higher zones. In many cases this will be ok because it's a GFP_HIGHMEM
    request of some description. On 64-bit, ZONE_DMA32 requests will cause
    some problems but 32-bit devices on 64-bit platforms are increasingly
    rare. Historically it would have been a major problem on 32-bit with big
    Highmem:Lowmem ratios but such configurations are also now rare and even
    where they exist, they are not encouraged. If it really becomes a problem,
    it'll manifest as very low reclaim efficiencies.

    Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
    ---
    mm/vmscan.c | 78 +++++++++++++++++++++++++++++++++++++------------------------
    1 file changed, 48 insertions(+), 30 deletions(-)

    diff --git a/mm/vmscan.c b/mm/vmscan.c
    index 760fdea19729..3e423993d374 100644
    --- a/mm/vmscan.c
    +++ b/mm/vmscan.c
    @@ -84,6 +84,9 @@ struct scan_control {
    /* Scan (total_size >> priority) pages at once */
    int priority;

    + /* The highest zone to isolate pages for reclaim from */
    + enum zone_type reclaim_idx;
    +
    unsigned int may_writepage:1;

    /* Can mapped pages be reclaimed? */
    @@ -1369,6 +1372,7 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
    struct list_head *src = &lruvec->lists[lru];
    unsigned long nr_taken = 0;
    unsigned long scan;
    + LIST_HEAD(pages_skipped);

    for (scan = 0; scan < nr_to_scan && nr_taken < nr_to_scan &&
    !list_empty(src); scan++) {
    @@ -1380,6 +1384,11 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,

    VM_BUG_ON_PAGE(!PageLRU(page), page);

    + if (page_zonenum(page) > sc->reclaim_idx) {
    + list_move(&page->lru, &pages_skipped);
    + continue;
    + }
    +
    switch (__isolate_lru_page(page, mode)) {
    case 0:
    nr_pages = hpage_nr_pages(page);
    @@ -1398,6 +1407,15 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
    }
    }

    + /*
    + * Splice any skipped pages to the start of the LRU list. Note that
    + * this disrupts the LRU order when reclaiming for lower zones but
    + * we cannot splice to the tail. If we did then the SWAP_CLUSTER_MAX
    + * scanning would soon rescan the same pages to skip and put the
    + * system at risk of premature OOM.
    + */
    + if (!list_empty(&pages_skipped))
    + list_splice(&pages_skipped, src);
    *nr_scanned = scan;
    trace_mm_vmscan_lru_isolate(sc->order, nr_to_scan, scan,
    nr_taken, mode, is_file_lru(lru));
    @@ -1560,7 +1578,7 @@ static int current_may_throttle(void)
    }

    /*
    - * shrink_inactive_list() is a helper for shrink_zone(). It returns the number
    + * shrink_inactive_list() is a helper for shrink_node(). It returns the number
    * of reclaimed pages
    */
    static noinline_for_stack unsigned long
    @@ -2394,12 +2412,14 @@ static inline bool should_continue_reclaim(struct zone *zone,
    }
    }

    -static bool shrink_zone(struct zone *zone, struct scan_control *sc,
    - bool is_classzone)
    +static bool shrink_node(pg_data_t *pgdat, struct scan_control *sc,
    + enum zone_type reclaim_idx,
    + enum zone_type classzone_idx)
    {
    struct reclaim_state *reclaim_state = current->reclaim_state;
    unsigned long nr_reclaimed, nr_scanned;
    bool reclaimable = false;
    + struct zone *zone = &pgdat->node_zones[classzone_idx];

    do {
    struct mem_cgroup *root = sc->target_mem_cgroup;
    @@ -2428,10 +2448,11 @@ static bool shrink_zone(struct zone *zone, struct scan_control *sc,
    reclaimed = sc->nr_reclaimed;
    scanned = sc->nr_scanned;

    + sc->reclaim_idx = reclaim_idx;
    shrink_zone_memcg(zone, memcg, sc, &lru_pages);
    zone_lru_pages += lru_pages;

    - if (memcg && is_classzone)
    + if (!global_reclaim(sc) && reclaim_idx == classzone_idx)
    shrink_slab(sc->gfp_mask, zone_to_nid(zone),
    memcg, sc->nr_scanned - scanned,
    lru_pages);
    @@ -2462,7 +2483,7 @@ static bool shrink_zone(struct zone *zone, struct scan_control *sc,
    * Shrink the slab caches in the same proportion that
    * the eligible LRU pages were scanned.
    */
    - if (global_reclaim(sc) && is_classzone)
    + if (global_reclaim(sc) && reclaim_idx == classzone_idx)
    shrink_slab(sc->gfp_mask, zone_to_nid(zone), NULL,
    sc->nr_scanned - nr_scanned,
    zone_lru_pages);
    @@ -2539,14 +2560,14 @@ static inline bool compaction_ready(struct zone *zone, int order)
    * If a zone is deemed to be full of pinned pages then just give it a light
    * scan then give up on it.
    */
    -static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
    +static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc,
    + enum zone_type reclaim_idx, enum zone_type classzone_idx)
    {
    struct zoneref *z;
    struct zone *zone;
    unsigned long nr_soft_reclaimed;
    unsigned long nr_soft_scanned;
    gfp_t orig_mask;
    - enum zone_type requested_highidx = gfp_zone(sc->gfp_mask);

    /*
    * If the number of buffer_heads in the machine exceeds the maximum
    @@ -2558,16 +2579,12 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
    sc->gfp_mask |= __GFP_HIGHMEM;

    for_each_zone_zonelist_nodemask(zone, z, zonelist,
    - requested_highidx, sc->nodemask) {
    - enum zone_type classzone_idx;
    -
    - if (!populated_zone(zone))
    - continue;
    -
    - classzone_idx = requested_highidx;
    - while (!populated_zone(zone->zone_pgdat->node_zones +
    - classzone_idx))
    + classzone_idx, sc->nodemask) {
    + if (!populated_zone(zone)) {
    + reclaim_idx--;
    classzone_idx--;
    + continue;
    + }

    /*
    * Take care memory controller reclaiming has small influence
    @@ -2593,7 +2610,7 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
    */
    if (IS_ENABLED(CONFIG_COMPACTION) &&
    sc->order > PAGE_ALLOC_COSTLY_ORDER &&
    - zonelist_zone_idx(z) <= requested_highidx &&
    + zonelist_zone_idx(z) <= classzone_idx &&
    compaction_ready(zone, sc->order)) {
    sc->compaction_ready = true;
    continue;
    @@ -2611,10 +2628,10 @@ static void shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
    &nr_soft_scanned);
    sc->nr_reclaimed += nr_soft_reclaimed;
    sc->nr_scanned += nr_soft_scanned;
    - /* need some check for avoid more shrink_zone() */
    + /* need some check for avoid more shrink_node() */
    }

    - shrink_zone(zone, sc, zone_idx(zone));
    + shrink_node(zone->zone_pgdat, sc, reclaim_idx, classzone_idx);
    }

    /*
    @@ -2646,6 +2663,7 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
    int initial_priority = sc->priority;
    unsigned long total_scanned = 0;
    unsigned long writeback_threshold;
    + enum zone_type classzone_idx = gfp_zone(sc->gfp_mask);
    retry:
    delayacct_freepages_start();

    @@ -2656,7 +2674,7 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
    vmpressure_prio(sc->gfp_mask, sc->target_mem_cgroup,
    sc->priority);
    sc->nr_scanned = 0;
    - shrink_zones(zonelist, sc);
    + shrink_zones(zonelist, sc, classzone_idx, classzone_idx);

    total_scanned += sc->nr_scanned;
    if (sc->nr_reclaimed >= sc->nr_to_reclaim)
    @@ -3112,7 +3130,7 @@ static bool kswapd_shrink_zone(struct zone *zone,
    balance_gap, classzone_idx))
    return true;

    - shrink_zone(zone, sc, zone_idx(zone) == classzone_idx);
    + shrink_node(zone->zone_pgdat, sc, zone_idx(zone), classzone_idx);

    /* TODO: ANOMALY */
    clear_bit(PGDAT_WRITEBACK, &pgdat->flags);
    @@ -3161,6 +3179,7 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
    unsigned long nr_soft_scanned;
    struct scan_control sc = {
    .gfp_mask = GFP_KERNEL,
    + .reclaim_idx = MAX_NR_ZONES - 1,
    .order = order,
    .priority = DEF_PRIORITY,
    .may_writepage = !laptop_mode,
    @@ -3231,15 +3250,14 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
    sc.may_writepage = 1;

    /*
    - * Now scan the zone in the dma->highmem direction, stopping
    - * at the last zone which needs scanning.
    - *
    - * We do this because the page allocator works in the opposite
    - * direction. This prevents the page allocator from allocating
    - * pages behind kswapd's direction of progress, which would
    - * cause too much scanning of the lower zones.
    + * Continue scanning in the highmem->dma direction stopping at
    + * the last zone which needs scanning. This may reclaim lowmem
    + * pages that are not necessary for zone balancing but it
    + * preserves LRU ordering. It is assumed that the bulk of
    + * allocation requests can use arbitrary zones with the
    + * possible exception of big highmem:lowmem configurations.
    */
    - for (i = 0; i <= end_zone; i++) {
    + for (i = end_zone; i >= end_zone; i--) {
    struct zone *zone = pgdat->node_zones + i;

    if (!populated_zone(zone))
    @@ -3717,7 +3735,7 @@ static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
    * priorities until we have enough memory freed.
    */
    do {
    - shrink_zone(zone, &sc, true);
    + shrink_node(zone->zone_pgdat, &sc, zone_idx(zone), zone_idx(zone));
    } while (sc.nr_reclaimed < nr_pages && --sc.priority >= 0);
    }

    --
    2.6.4
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