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    Subject[PATCH 08/15] mm: scalable bdi statistics counters.
    Provide scalable per backing_dev_info statistics counters.

    Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    ---
    include/linux/backing-dev.h | 96 +++++++++++++++++++++++++++++++++++++++++++-
    mm/backing-dev.c | 21 +++++++++
    2 files changed, 115 insertions(+), 2 deletions(-)

    Index: linux-2.6/include/linux/backing-dev.h
    ===================================================================
    --- linux-2.6.orig/include/linux/backing-dev.h 2007-05-10 10:21:53.000000000 +0200
    +++ linux-2.6/include/linux/backing-dev.h 2007-05-10 10:23:26.000000000 +0200
    @@ -8,6 +8,8 @@
    #ifndef _LINUX_BACKING_DEV_H
    #define _LINUX_BACKING_DEV_H

    +#include <linux/percpu_counter.h>
    +#include <linux/log2.h>
    #include <asm/atomic.h>

    struct page;
    @@ -24,6 +26,12 @@ enum bdi_state {

    typedef int (congested_fn)(void *, int);

    +enum bdi_stat_item {
    + NR_BDI_STAT_ITEMS
    +};
    +
    +#define BDI_STAT_BATCH (8*(1+ilog2(nr_cpu_ids)))
    +
    struct backing_dev_info {
    unsigned long ra_pages; /* max readahead in PAGE_CACHE_SIZE units */
    unsigned long state; /* Always use atomic bitops on this */
    @@ -32,14 +40,98 @@ struct backing_dev_info {
    void *congested_data; /* Pointer to aux data for congested func */
    void (*unplug_io_fn)(struct backing_dev_info *, struct page *);
    void *unplug_io_data;
    +
    + struct percpu_counter bdi_stat[NR_BDI_STAT_ITEMS];
    };

    -static inline void bdi_init(struct backing_dev_info *bdi)
    +void bdi_init(struct backing_dev_info *bdi);
    +void bdi_destroy(struct backing_dev_info *bdi);
    +
    +static inline void __mod_bdi_stat(struct backing_dev_info *bdi,
    + enum bdi_stat_item item, s32 amount)
    +{
    + __percpu_counter_mod(&bdi->bdi_stat[item], amount, BDI_STAT_BATCH);
    +}
    +
    +static inline void __mod_bdi_stat64(struct backing_dev_info *bdi,
    + enum bdi_stat_item item, s64 amount)
    +{
    + __percpu_counter_mod64(&bdi->bdi_stat[item], amount, BDI_STAT_BATCH);
    +}
    +
    +static inline void __inc_bdi_stat(struct backing_dev_info *bdi,
    + enum bdi_stat_item item)
    +{
    + __mod_bdi_stat(bdi, item, 1);
    +}
    +
    +static inline void inc_bdi_stat(struct backing_dev_info *bdi,
    + enum bdi_stat_item item)
    +{
    + unsigned long flags;
    +
    + local_irq_save(flags);
    + __inc_bdi_stat(bdi, item);
    + local_irq_restore(flags);
    +}
    +
    +static inline void __dec_bdi_stat(struct backing_dev_info *bdi,
    + enum bdi_stat_item item)
    {
    + __mod_bdi_stat(bdi, item, -1);
    }

    -static inline void bdi_destroy(struct backing_dev_info *bdi)
    +static inline void dec_bdi_stat(struct backing_dev_info *bdi,
    + enum bdi_stat_item item)
    {
    + unsigned long flags;
    +
    + local_irq_save(flags);
    + __dec_bdi_stat(bdi, item);
    + local_irq_restore(flags);
    +}
    +
    +static inline u64 bdi_stat_unsigned(struct backing_dev_info *bdi,
    + enum bdi_stat_item item)
    +{
    + return percpu_counter_read(&bdi->bdi_stat[item]);
    +}
    +
    +static inline s64 bdi_stat(struct backing_dev_info *bdi,
    + enum bdi_stat_item item)
    +{
    + return percpu_counter_read_positive(&bdi->bdi_stat[item]);
    +}
    +
    +static inline s64 __bdi_stat_sum(struct backing_dev_info *bdi,
    + enum bdi_stat_item item)
    +{
    + return percpu_counter_sum(&bdi->bdi_stat[item]);
    +}
    +
    +static inline s64 bdi_stat_sum(struct backing_dev_info *bdi,
    + enum bdi_stat_item item)
    +{
    + s64 sum;
    + unsigned long flags;
    +
    + local_irq_save(flags);
    + sum = __bdi_stat_sum(bdi, item);
    + local_irq_restore(flags);
    +
    + return sum;
    +}
    +
    +/*
    + * maximal error of a stat counter.
    + */
    +static inline unsigned long bdi_stat_error(struct backing_dev_info *bdi)
    +{
    +#ifdef CONFIG_SMP
    + return nr_cpu_ids * BDI_STAT_BATCH;
    +#else
    + return 1;
    +#endif
    }

    /*
    Index: linux-2.6/mm/backing-dev.c
    ===================================================================
    --- linux-2.6.orig/mm/backing-dev.c 2007-05-10 10:21:46.000000000 +0200
    +++ linux-2.6/mm/backing-dev.c 2007-05-10 10:23:08.000000000 +0200
    @@ -5,6 +5,24 @@
    #include <linux/sched.h>
    #include <linux/module.h>

    +void bdi_init(struct backing_dev_info *bdi)
    +{
    + int i;
    +
    + for (i = 0; i < NR_BDI_STAT_ITEMS; i++)
    + percpu_counter_init(&bdi->bdi_stat[i], 0);
    +}
    +EXPORT_SYMBOL(bdi_init);
    +
    +void bdi_destroy(struct backing_dev_info *bdi)
    +{
    + int i;
    +
    + for (i = 0; i < NR_BDI_STAT_ITEMS; i++)
    + percpu_counter_destroy(&bdi->bdi_stat[i]);
    +}
    +EXPORT_SYMBOL(bdi_destroy);
    +
    static wait_queue_head_t congestion_wqh[2] = {
    __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[0]),
    __WAIT_QUEUE_HEAD_INITIALIZER(congestion_wqh[1])
    --

    -
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