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    SubjectRe: [patch 3/3] mm: vmscan: clean up struct scan_control
    On Mon, Jul 14, 2014 at 12:46:21PM -0700, Hugh Dickins wrote:
    > 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.

    Good point, I didn't even think of that. Thanks!

    Andrew, could you please replace this patch with the following?

    ---
    From bbe8c1645c77297a96ecd5d64d659ddcd6984d03 Mon Sep 17 00:00:00 2001
    From: Johannes Weiner <hannes@cmpxchg.org>
    Date: Mon, 14 Jul 2014 08:51:54 -0400
    Subject: [patch] mm: vmscan: clean up struct scan_control

    Reorder the members by input and output, then turn the individual
    integers for may_writepage, may_unmap, may_swap, compaction_ready,
    hibernation_mode into bit fields to save stack space:

    +72/-296 -224
    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

    Suggested-by: Mel Gorman <mgorman@suse.de>
    Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
    ---
    mm/vmscan.c | 99 ++++++++++++++++++++++++++++---------------------------------
    1 file changed, 46 insertions(+), 53 deletions(-)

    diff --git a/mm/vmscan.c b/mm/vmscan.c
    index c28b8981e56a..81dd858b9d17 100644
    --- a/mm/vmscan.c
    +++ b/mm/vmscan.c
    @@ -59,35 +59,20 @@
    #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;
    -
    /* 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 +80,27 @@ 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;
    +
    + unsigned int may_writepage:1;
    +
    + /* Can mapped pages be reclaimed? */
    + unsigned int may_unmap:1;
    +
    + /* Can pages be swapped as part of reclaim? */
    + unsigned int may_swap:1;
    +
    + unsigned int hibernation_mode:1;
    +
    + /* One of the zones is ready for compaction */
    + unsigned int compaction_ready:1;
    +
    + /* 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))
    @@ -2668,15 +2669,14 @@ unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
    {
    unsigned long nr_reclaimed;
    struct scan_control sc = {
    + .nr_to_reclaim = SWAP_CLUSTER_MAX,
    .gfp_mask = (gfp_mask = memalloc_noio_flags(gfp_mask)),
    + .order = order,
    + .nodemask = nodemask,
    + .priority = DEF_PRIORITY,
    .may_writepage = !laptop_mode,
    - .nr_to_reclaim = SWAP_CLUSTER_MAX,
    .may_unmap = 1,
    .may_swap = 1,
    - .order = order,
    - .priority = DEF_PRIORITY,
    - .target_mem_cgroup = NULL,
    - .nodemask = nodemask,
    };

    /*
    @@ -2706,14 +2706,11 @@ 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,
    + .target_mem_cgroup = memcg,
    .may_writepage = !laptop_mode,
    .may_unmap = 1,
    .may_swap = !noswap,
    - .order = 0,
    - .priority = 0,
    - .target_mem_cgroup = memcg,
    };
    struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
    int swappiness = mem_cgroup_swappiness(memcg);
    @@ -2748,16 +2745,14 @@ 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),
    + .target_mem_cgroup = memcg,
    + .priority = DEF_PRIORITY,
    + .may_writepage = !laptop_mode,
    + .may_unmap = 1,
    + .may_swap = !noswap,
    };

    /*
    @@ -3015,12 +3010,11 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
    unsigned long nr_soft_scanned;
    struct scan_control sc = {
    .gfp_mask = GFP_KERNEL,
    + .order = order,
    .priority = DEF_PRIORITY,
    + .may_writepage = !laptop_mode,
    .may_unmap = 1,
    .may_swap = 1,
    - .may_writepage = !laptop_mode,
    - .order = order,
    - .target_mem_cgroup = NULL,
    };
    count_vm_event(PAGEOUTRUN);

    @@ -3401,14 +3395,13 @@ unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
    {
    struct reclaim_state reclaim_state;
    struct scan_control sc = {
    + .nr_to_reclaim = nr_to_reclaim,
    .gfp_mask = GFP_HIGHUSER_MOVABLE,
    - .may_swap = 1,
    - .may_unmap = 1,
    + .priority = DEF_PRIORITY,
    .may_writepage = 1,
    - .nr_to_reclaim = nr_to_reclaim,
    + .may_unmap = 1,
    + .may_swap = 1,
    .hibernation_mode = 1,
    - .order = 0,
    - .priority = DEF_PRIORITY,
    };
    struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
    struct task_struct *p = current;
    @@ -3588,13 +3581,13 @@ 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,
    + .may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE),
    + .may_unmap = !!(zone_reclaim_mode & RECLAIM_SWAP),
    + .may_swap = 1,
    };
    struct shrink_control shrink = {
    .gfp_mask = sc.gfp_mask,
    --
    2.0.0


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