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    SubjectRe: [patch 3/3] mm: vmscan: clean up struct scan_control
    On Mon, 14 Jul 2014, Johannes Weiner wrote:

    > Reorder the members by input and output, then turn the individual
    > integers for may_writepage, may_unmap, may_swap, compaction_ready,
    > hibernation_mode into flags that fit into a single integer.
    >
    > Stack delta: +72/-296 -224 old new delta
    > kswapd 104 176 +72
    > try_to_free_pages 80 56 -24
    > try_to_free_mem_cgroup_pages 80 56 -24
    > shrink_all_memory 88 64 -24
    > reclaim_clean_pages_from_list 168 144 -24
    > mem_cgroup_shrink_node_zone 104 80 -24
    > __zone_reclaim 176 152 -24
    > balance_pgdat 152 - -152
    >
    > text data bss dec hex filename
    > 38151 5641 16 43808 ab20 mm/vmscan.o.old
    > 38047 5641 16 43704 aab8 mm/vmscan.o
    >
    > Suggested-by: Mel Gorman <mgorman@suse.de>
    > Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
    > ---
    > mm/vmscan.c | 158 ++++++++++++++++++++++++++++++------------------------------
    > 1 file changed, 78 insertions(+), 80 deletions(-)
    >
    > diff --git a/mm/vmscan.c b/mm/vmscan.c
    > index c28b8981e56a..73d8e69ff3eb 100644
    > --- a/mm/vmscan.c
    > +++ b/mm/vmscan.c
    > @@ -58,36 +58,28 @@
    > #define CREATE_TRACE_POINTS
    > #include <trace/events/vmscan.h>
    >
    > -struct scan_control {
    > - /* Incremented by the number of inactive pages that were scanned */
    > - unsigned long nr_scanned;
    > -
    > - /* Number of pages freed so far during a call to shrink_zones() */
    > - unsigned long nr_reclaimed;
    > -
    > - /* One of the zones is ready for compaction */
    > - int compaction_ready;
    > +/* Scan control flags */
    > +#define MAY_WRITEPAGE 0x1
    > +#define MAY_UNMAP 0x2
    > +#define MAY_SWAP 0x4
    > +#define MAY_SKIP_CONGESTION 0x8
    > +#define COMPACTION_READY 0x10
    >
    > +struct scan_control {
    > /* How many pages shrink_list() should reclaim */
    > unsigned long nr_to_reclaim;
    >
    > - unsigned long hibernation_mode;
    > -
    > /* This context's GFP mask */
    > gfp_t gfp_mask;
    >
    > - int may_writepage;
    > -
    > - /* Can mapped pages be reclaimed? */
    > - int may_unmap;
    > -
    > - /* Can pages be swapped as part of reclaim? */
    > - int may_swap;
    > -
    > + /* Allocation order */
    > int order;
    >
    > - /* Scan (total_size >> priority) pages at once */
    > - int priority;
    > + /*
    > + * Nodemask of nodes allowed by the caller. If NULL, all nodes
    > + * are scanned.
    > + */
    > + nodemask_t *nodemask;
    >
    > /*
    > * The memory cgroup that hit its limit and as a result is the
    > @@ -95,11 +87,17 @@ struct scan_control {
    > */
    > struct mem_cgroup *target_mem_cgroup;
    >
    > - /*
    > - * Nodemask of nodes allowed by the caller. If NULL, all nodes
    > - * are scanned.
    > - */
    > - nodemask_t *nodemask;
    > + /* Scan (total_size >> priority) pages at once */
    > + int priority;
    > +
    > + /* Scan control flags; see above */
    > + unsigned int flags;

    This seems to result in a fair amount of unnecessary churn:
    why not just put may_writepage etc into an unsigned int bitfield,
    then you get the saving without changing all the rest of the code.

    Hugh

    > +
    > + /* Incremented by the number of inactive pages that were scanned */
    > + unsigned long nr_scanned;
    > +
    > + /* Number of pages freed so far during a call to shrink_zones() */
    > + unsigned long nr_reclaimed;
    > };
    >
    > #define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
    > @@ -840,7 +838,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
    > if (unlikely(!page_evictable(page)))
    > goto cull_mlocked;
    >
    > - if (!sc->may_unmap && page_mapped(page))
    > + if (!(sc->flags & MAY_UNMAP) && page_mapped(page))
    > goto keep_locked;
    >
    > /* Double the slab pressure for mapped and swapcache pages */
    > @@ -1014,7 +1012,7 @@ static unsigned long shrink_page_list(struct list_head *page_list,
    > goto keep_locked;
    > if (!may_enter_fs)
    > goto keep_locked;
    > - if (!sc->may_writepage)
    > + if (!(sc->flags & MAY_WRITEPAGE))
    > goto keep_locked;
    >
    > /* Page is dirty, try to write it out here */
    > @@ -1146,7 +1144,7 @@ unsigned long reclaim_clean_pages_from_list(struct zone *zone,
    > struct scan_control sc = {
    > .gfp_mask = GFP_KERNEL,
    > .priority = DEF_PRIORITY,
    > - .may_unmap = 1,
    > + .flags = MAY_UNMAP,
    > };
    > unsigned long ret, dummy1, dummy2, dummy3, dummy4, dummy5;
    > struct page *page, *next;
    > @@ -1489,9 +1487,9 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
    >
    > lru_add_drain();
    >
    > - if (!sc->may_unmap)
    > + if (!(sc->flags & MAY_UNMAP))
    > isolate_mode |= ISOLATE_UNMAPPED;
    > - if (!sc->may_writepage)
    > + if (!(sc->flags & MAY_WRITEPAGE))
    > isolate_mode |= ISOLATE_CLEAN;
    >
    > spin_lock_irq(&zone->lru_lock);
    > @@ -1593,7 +1591,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
    > * is congested. Allow kswapd to continue until it starts encountering
    > * unqueued dirty pages or cycling through the LRU too quickly.
    > */
    > - if (!sc->hibernation_mode && !current_is_kswapd() &&
    > + if (!(sc->flags & MAY_SKIP_CONGESTION) && !current_is_kswapd() &&
    > current_may_throttle())
    > wait_iff_congested(zone, BLK_RW_ASYNC, HZ/10);
    >
    > @@ -1683,9 +1681,9 @@ static void shrink_active_list(unsigned long nr_to_scan,
    >
    > lru_add_drain();
    >
    > - if (!sc->may_unmap)
    > + if (!(sc->flags & MAY_UNMAP))
    > isolate_mode |= ISOLATE_UNMAPPED;
    > - if (!sc->may_writepage)
    > + if (!(sc->flags & MAY_WRITEPAGE))
    > isolate_mode |= ISOLATE_CLEAN;
    >
    > spin_lock_irq(&zone->lru_lock);
    > @@ -1897,7 +1895,7 @@ static void get_scan_count(struct lruvec *lruvec, int swappiness,
    > force_scan = true;
    >
    > /* If we have no swap space, do not bother scanning anon pages. */
    > - if (!sc->may_swap || (get_nr_swap_pages() <= 0)) {
    > + if (!(sc->flags & MAY_SWAP) || (get_nr_swap_pages() <= 0)) {
    > scan_balance = SCAN_FILE;
    > goto out;
    > }
    > @@ -2406,7 +2404,7 @@ static bool shrink_zones(struct zonelist *zonelist, struct scan_control *sc)
    > sc->order > PAGE_ALLOC_COSTLY_ORDER &&
    > zonelist_zone_idx(z) <= requested_highidx &&
    > compaction_ready(zone, sc->order)) {
    > - sc->compaction_ready = true;
    > + sc->flags |= COMPACTION_READY;
    > continue;
    > }
    >
    > @@ -2496,7 +2494,7 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
    > if (sc->nr_reclaimed >= sc->nr_to_reclaim)
    > break;
    >
    > - if (sc->compaction_ready)
    > + if (sc->flags & COMPACTION_READY)
    > break;
    >
    > /*
    > @@ -2504,7 +2502,7 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
    > * writepage even in laptop mode.
    > */
    > if (sc->priority < DEF_PRIORITY - 2)
    > - sc->may_writepage = 1;
    > + sc->flags |= MAY_WRITEPAGE;
    >
    > /*
    > * Try to write back as many pages as we just scanned. This
    > @@ -2517,7 +2515,7 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
    > if (total_scanned > writeback_threshold) {
    > wakeup_flusher_threads(laptop_mode ? 0 : total_scanned,
    > WB_REASON_TRY_TO_FREE_PAGES);
    > - sc->may_writepage = 1;
    > + sc->flags |= MAY_WRITEPAGE;
    > }
    > } while (--sc->priority >= 0);
    >
    > @@ -2527,7 +2525,7 @@ static unsigned long do_try_to_free_pages(struct zonelist *zonelist,
    > return sc->nr_reclaimed;
    >
    > /* Aborted reclaim to try compaction? don't OOM, then */
    > - if (sc->compaction_ready)
    > + if (sc->flags & COMPACTION_READY)
    > return 1;
    >
    > /* Any of the zones still reclaimable? Don't OOM. */
    > @@ -2668,17 +2666,17 @@ unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
    > {
    > unsigned long nr_reclaimed;
    > struct scan_control sc = {
    > - .gfp_mask = (gfp_mask = memalloc_noio_flags(gfp_mask)),
    > - .may_writepage = !laptop_mode,
    > .nr_to_reclaim = SWAP_CLUSTER_MAX,
    > - .may_unmap = 1,
    > - .may_swap = 1,
    > + .gfp_mask = (gfp_mask = memalloc_noio_flags(gfp_mask)),
    > .order = order,
    > - .priority = DEF_PRIORITY,
    > - .target_mem_cgroup = NULL,
    > .nodemask = nodemask,
    > + .priority = DEF_PRIORITY,
    > + .flags = MAY_UNMAP | MAY_SWAP,
    > };
    >
    > + if (!laptop_mode)
    > + sc.flags |= MAY_WRITEPAGE;
    > +
    > /*
    > * Do not enter reclaim if fatal signal was delivered while throttled.
    > * 1 is returned so that the page allocator does not OOM kill at this
    > @@ -2688,7 +2686,7 @@ unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
    > return 1;
    >
    > trace_mm_vmscan_direct_reclaim_begin(order,
    > - sc.may_writepage,
    > + sc.flags & MAY_WRITEPAGE,
    > gfp_mask);
    >
    > nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
    > @@ -2706,23 +2704,22 @@ unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *memcg,
    > unsigned long *nr_scanned)
    > {
    > struct scan_control sc = {
    > - .nr_scanned = 0,
    > .nr_to_reclaim = SWAP_CLUSTER_MAX,
    > - .may_writepage = !laptop_mode,
    > - .may_unmap = 1,
    > - .may_swap = !noswap,
    > - .order = 0,
    > - .priority = 0,
    > + .gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
    > + (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK),
    > .target_mem_cgroup = memcg,
    > + .flags = MAY_UNMAP,
    > };
    > struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
    > int swappiness = mem_cgroup_swappiness(memcg);
    >
    > - sc.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
    > - (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK);
    > + if (!laptop_mode)
    > + sc.flags |= MAY_WRITEPAGE;
    > + if (!noswap)
    > + sc.flags |= MAY_SWAP;
    >
    > trace_mm_vmscan_memcg_softlimit_reclaim_begin(sc.order,
    > - sc.may_writepage,
    > + sc.flags & MAY_WRITEPAGE,
    > sc.gfp_mask);
    >
    > /*
    > @@ -2748,18 +2745,19 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
    > unsigned long nr_reclaimed;
    > int nid;
    > struct scan_control sc = {
    > - .may_writepage = !laptop_mode,
    > - .may_unmap = 1,
    > - .may_swap = !noswap,
    > .nr_to_reclaim = SWAP_CLUSTER_MAX,
    > - .order = 0,
    > - .priority = DEF_PRIORITY,
    > - .target_mem_cgroup = memcg,
    > - .nodemask = NULL, /* we don't care the placement */
    > .gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
    > - (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK),
    > + (GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK),
    > + .target_mem_cgroup = memcg,
    > + .priority = DEF_PRIORITY,
    > + .flags = MAY_UNMAP,
    > };
    >
    > + if (!laptop_mode)
    > + sc.flags |= MAY_WRITEPAGE;
    > + if (!noswap)
    > + sc.flags |= MAY_SWAP;
    > +
    > /*
    > * Unlike direct reclaim via alloc_pages(), memcg's reclaim doesn't
    > * take care of from where we get pages. So the node where we start the
    > @@ -2770,7 +2768,7 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
    > zonelist = NODE_DATA(nid)->node_zonelists;
    >
    > trace_mm_vmscan_memcg_reclaim_begin(0,
    > - sc.may_writepage,
    > + sc.flags & MAY_WRITEPAGE,
    > sc.gfp_mask);
    >
    > nr_reclaimed = do_try_to_free_pages(zonelist, &sc);
    > @@ -3015,15 +3013,15 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
    > unsigned long nr_soft_scanned;
    > struct scan_control sc = {
    > .gfp_mask = GFP_KERNEL,
    > - .priority = DEF_PRIORITY,
    > - .may_unmap = 1,
    > - .may_swap = 1,
    > - .may_writepage = !laptop_mode,
    > .order = order,
    > - .target_mem_cgroup = NULL,
    > + .priority = DEF_PRIORITY,
    > + .flags = MAY_UNMAP | MAY_SWAP,
    > };
    > count_vm_event(PAGEOUTRUN);
    >
    > + if (!laptop_mode)
    > + sc.flags |= MAY_WRITEPAGE;
    > +
    > do {
    > unsigned long lru_pages = 0;
    > unsigned long nr_attempted = 0;
    > @@ -3104,7 +3102,7 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
    > * even in laptop mode.
    > */
    > if (sc.priority < DEF_PRIORITY - 2)
    > - sc.may_writepage = 1;
    > + sc.flags |= MAY_WRITEPAGE;
    >
    > /*
    > * Now scan the zone in the dma->highmem direction, stopping
    > @@ -3401,14 +3399,11 @@ unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
    > {
    > struct reclaim_state reclaim_state;
    > struct scan_control sc = {
    > - .gfp_mask = GFP_HIGHUSER_MOVABLE,
    > - .may_swap = 1,
    > - .may_unmap = 1,
    > - .may_writepage = 1,
    > .nr_to_reclaim = nr_to_reclaim,
    > - .hibernation_mode = 1,
    > - .order = 0,
    > + .gfp_mask = GFP_HIGHUSER_MOVABLE,
    > .priority = DEF_PRIORITY,
    > + .flags = MAY_WRITEPAGE | MAY_UNMAP | MAY_SWAP |
    > + MAY_SKIP_CONGESTION,
    > };
    > struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
    > struct task_struct *p = current;
    > @@ -3588,19 +3583,22 @@ static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
    > struct task_struct *p = current;
    > struct reclaim_state reclaim_state;
    > struct scan_control sc = {
    > - .may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE),
    > - .may_unmap = !!(zone_reclaim_mode & RECLAIM_SWAP),
    > - .may_swap = 1,
    > .nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
    > .gfp_mask = (gfp_mask = memalloc_noio_flags(gfp_mask)),
    > .order = order,
    > .priority = ZONE_RECLAIM_PRIORITY,
    > + .flags = MAY_SWAP,
    > };
    > struct shrink_control shrink = {
    > .gfp_mask = sc.gfp_mask,
    > };
    > unsigned long nr_slab_pages0, nr_slab_pages1;
    >
    > + if (zone_reclaim_mode & RECLAIM_WRITE)
    > + sc.flags |= MAY_WRITEPAGE;
    > + if (zone_reclaim_mode & RECLAIM_SWAP)
    > + sc.flags |= MAY_UNMAP;
    > +
    > cond_resched();
    > /*
    > * We need to be able to allocate from the reserves for RECLAIM_SWAP
    > --
    > 2.0.0


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