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    Subject[PATCH 3/3] Provide control over unmapped pages (v4)
    From
    Date
    Changelog v4
    1. Add max_unmapped_ratio and use that as the upper limit
    to check when to shrink the unmapped page cache (Christoph
    Lameter)

    Changelog v2
    1. Use a config option to enable the code (Andrew Morton)
    2. Explain the magic tunables in the code or at-least attempt
    to explain them (General comment)
    3. Hint uses of the boot parameter with unlikely (Andrew Morton)
    4. Use better names (balanced is not a good naming convention)

    Provide control using zone_reclaim() and a boot parameter. The
    code reuses functionality from zone_reclaim() to isolate unmapped
    pages and reclaim them as a priority, ahead of other mapped pages.
    A new sysctl for max_unmapped_ratio is provided and set to 16,
    indicating 16% of the total zone pages are unmapped, we start
    shrinking unmapped page cache.

    Signed-off-by: Balbir Singh <balbir@linux.vnet.ibm.com>
    ---
    Documentation/kernel-parameters.txt | 8 +++
    include/linux/mmzone.h | 5 ++
    include/linux/swap.h | 23 ++++++++-
    init/Kconfig | 12 +++++
    kernel/sysctl.c | 11 ++++
    mm/page_alloc.c | 25 ++++++++++
    mm/vmscan.c | 87 +++++++++++++++++++++++++++++++++++
    7 files changed, 166 insertions(+), 5 deletions(-)

    diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
    index fee5f57..65a4ee6 100644
    --- a/Documentation/kernel-parameters.txt
    +++ b/Documentation/kernel-parameters.txt
    @@ -2500,6 +2500,14 @@ and is between 256 and 4096 characters. It is defined in the file
    [X86]
    Set unknown_nmi_panic=1 early on boot.

    + unmapped_page_control
    + [KNL] Available if CONFIG_UNMAPPED_PAGECACHE_CONTROL
    + is enabled. It controls the amount of unmapped memory
    + that is present in the system. This boot option plus
    + vm.min_unmapped_ratio (sysctl) provide granular control
    + over how much unmapped page cache can exist in the system
    + before kswapd starts reclaiming unmapped page cache pages.
    +
    usbcore.autosuspend=
    [USB] The autosuspend time delay (in seconds) used
    for newly-detected USB devices (default 2). This
    diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
    index 2485acc..18f0f09 100644
    --- a/include/linux/mmzone.h
    +++ b/include/linux/mmzone.h
    @@ -306,7 +306,10 @@ struct zone {
    /*
    * zone reclaim becomes active if more unmapped pages exist.
    */
    +#if defined(CONFIG_UNMAPPED_PAGE_CONTROL) || defined(CONFIG_NUMA)
    unsigned long min_unmapped_pages;
    + unsigned long max_unmapped_pages;
    +#endif
    #ifdef CONFIG_NUMA
    int node;
    unsigned long min_slab_pages;
    @@ -773,6 +776,8 @@ int percpu_pagelist_fraction_sysctl_handler(struct ctl_table *, int,
    void __user *, size_t *, loff_t *);
    int sysctl_min_unmapped_ratio_sysctl_handler(struct ctl_table *, int,
    void __user *, size_t *, loff_t *);
    +int sysctl_max_unmapped_ratio_sysctl_handler(struct ctl_table *, int,
    + void __user *, size_t *, loff_t *);
    int sysctl_min_slab_ratio_sysctl_handler(struct ctl_table *, int,
    void __user *, size_t *, loff_t *);

    diff --git a/include/linux/swap.h b/include/linux/swap.h
    index 7b75626..ae62a03 100644
    --- a/include/linux/swap.h
    +++ b/include/linux/swap.h
    @@ -255,19 +255,34 @@ extern int vm_swappiness;
    extern int remove_mapping(struct address_space *mapping, struct page *page);
    extern long vm_total_pages;

    +#if defined(CONFIG_UNMAPPED_PAGECACHE_CONTROL) || defined(CONFIG_NUMA)
    extern int sysctl_min_unmapped_ratio;
    +extern int sysctl_max_unmapped_ratio;
    +
    extern int zone_reclaim(struct zone *, gfp_t, unsigned int);
    -#ifdef CONFIG_NUMA
    -extern int zone_reclaim_mode;
    -extern int sysctl_min_slab_ratio;
    #else
    -#define zone_reclaim_mode 0
    static inline int zone_reclaim(struct zone *z, gfp_t mask, unsigned int order)
    {
    return 0;
    }
    #endif

    +#if defined(CONFIG_UNMAPPED_PAGECACHE_CONTROL)
    +extern bool should_reclaim_unmapped_pages(struct zone *zone);
    +#else
    +static inline bool should_reclaim_unmapped_pages(struct zone *zone)
    +{
    + return false;
    +}
    +#endif
    +
    +#ifdef CONFIG_NUMA
    +extern int zone_reclaim_mode;
    +extern int sysctl_min_slab_ratio;
    +#else
    +#define zone_reclaim_mode 0
    +#endif
    +
    extern int page_evictable(struct page *page, struct vm_area_struct *vma);
    extern void scan_mapping_unevictable_pages(struct address_space *);

    diff --git a/init/Kconfig b/init/Kconfig
    index 4f6cdbf..2dfbc09 100644
    --- a/init/Kconfig
    +++ b/init/Kconfig
    @@ -828,6 +828,18 @@ config SCHED_AUTOGROUP
    config MM_OWNER
    bool

    +config UNMAPPED_PAGECACHE_CONTROL
    + bool "Provide control over unmapped page cache"
    + default n
    + help
    + This option adds support for controlling unmapped page cache
    + via a boot parameter (unmapped_page_control). The boot parameter
    + with sysctl (vm.min_unmapped_ratio) control the total number
    + of unmapped pages in the system. This feature is useful if
    + you want to limit the amount of unmapped page cache or want
    + to reduce page cache duplication in a virtualized environment.
    + If unsure say 'N'
    +
    config SYSFS_DEPRECATED
    bool "enable deprecated sysfs features to support old userspace tools"
    depends on SYSFS
    diff --git a/kernel/sysctl.c b/kernel/sysctl.c
    index 12e8f26..63dbba6 100644
    --- a/kernel/sysctl.c
    +++ b/kernel/sysctl.c
    @@ -1224,6 +1224,7 @@ static struct ctl_table vm_table[] = {
    .extra1 = &zero,
    },
    #endif
    +#if defined(CONFIG_UNMAPPED_PAGE_CONTROL) || defined(CONFIG_NUMA)
    {
    .procname = "min_unmapped_ratio",
    .data = &sysctl_min_unmapped_ratio,
    @@ -1233,6 +1234,16 @@ static struct ctl_table vm_table[] = {
    .extra1 = &zero,
    .extra2 = &one_hundred,
    },
    + {
    + .procname = "max_unmapped_ratio",
    + .data = &sysctl_max_unmapped_ratio,
    + .maxlen = sizeof(sysctl_max_unmapped_ratio),
    + .mode = 0644,
    + .proc_handler = sysctl_max_unmapped_ratio_sysctl_handler,
    + .extra1 = &zero,
    + .extra2 = &one_hundred,
    + },
    +#endif
    #ifdef CONFIG_NUMA
    {
    .procname = "zone_reclaim_mode",
    diff --git a/mm/page_alloc.c b/mm/page_alloc.c
    index 7b56473..2ac8549 100644
    --- a/mm/page_alloc.c
    +++ b/mm/page_alloc.c
    @@ -1660,6 +1660,9 @@ zonelist_scan:
    unsigned long mark;
    int ret;

    + if (should_reclaim_unmapped_pages(zone))
    + wakeup_kswapd(zone, order, classzone_idx);
    +
    mark = zone->watermark[alloc_flags & ALLOC_WMARK_MASK];
    if (zone_watermark_ok(zone, order, mark,
    classzone_idx, alloc_flags))
    @@ -4167,8 +4170,12 @@ static void __paginginit free_area_init_core(struct pglist_data *pgdat,

    zone->spanned_pages = size;
    zone->present_pages = realsize;
    +#if defined(CONFIG_UNMAPPED_PAGE_CONTROL) || defined(CONFIG_NUMA)
    zone->min_unmapped_pages = (realsize*sysctl_min_unmapped_ratio)
    / 100;
    + zone->max_unmapped_pages = (realsize*sysctl_max_unmapped_ratio)
    + / 100;
    +#endif
    #ifdef CONFIG_NUMA
    zone->node = nid;
    zone->min_slab_pages = (realsize * sysctl_min_slab_ratio) / 100;
    @@ -5084,6 +5091,7 @@ int min_free_kbytes_sysctl_handler(ctl_table *table, int write,
    return 0;
    }

    +#if defined(CONFIG_UNMAPPED_PAGE_CONTROL) || defined(CONFIG_NUMA)
    int sysctl_min_unmapped_ratio_sysctl_handler(ctl_table *table, int write,
    void __user *buffer, size_t *length, loff_t *ppos)
    {
    @@ -5100,6 +5108,23 @@ int sysctl_min_unmapped_ratio_sysctl_handler(ctl_table *table, int write,
    return 0;
    }

    +int sysctl_max_unmapped_ratio_sysctl_handler(ctl_table *table, int write,
    + void __user *buffer, size_t *length, loff_t *ppos)
    +{
    + struct zone *zone;
    + int rc;
    +
    + rc = proc_dointvec_minmax(table, write, buffer, length, ppos);
    + if (rc)
    + return rc;
    +
    + for_each_zone(zone)
    + zone->max_unmapped_pages = (zone->present_pages *
    + sysctl_max_unmapped_ratio) / 100;
    + return 0;
    +}
    +#endif
    +
    #ifdef CONFIG_NUMA
    int sysctl_min_slab_ratio_sysctl_handler(ctl_table *table, int write,
    void __user *buffer, size_t *length, loff_t *ppos)
    diff --git a/mm/vmscan.c b/mm/vmscan.c
    index 02cc82e..6377411 100644
    --- a/mm/vmscan.c
    +++ b/mm/vmscan.c
    @@ -159,6 +159,29 @@ static DECLARE_RWSEM(shrinker_rwsem);
    #define scanning_global_lru(sc) (1)
    #endif

    +#if defined(CONFIG_UNMAPPED_PAGECACHE_CONTROL)
    +static unsigned long reclaim_unmapped_pages(int priority, struct zone *zone,
    + struct scan_control *sc);
    +static int unmapped_page_control __read_mostly;
    +
    +static int __init unmapped_page_control_parm(char *str)
    +{
    + unmapped_page_control = 1;
    + /*
    + * XXX: Should we tweak swappiness here?
    + */
    + return 1;
    +}
    +__setup("unmapped_page_control", unmapped_page_control_parm);
    +
    +#else /* !CONFIG_UNMAPPED_PAGECACHE_CONTROL */
    +static inline unsigned long reclaim_unmapped_pages(int priority,
    + struct zone *zone, struct scan_control *sc)
    +{
    + return 0;
    +}
    +#endif
    +
    static struct zone_reclaim_stat *get_reclaim_stat(struct zone *zone,
    struct scan_control *sc)
    {
    @@ -2359,6 +2382,12 @@ loop_again:
    shrink_active_list(SWAP_CLUSTER_MAX, zone,
    &sc, priority, 0);

    + /*
    + * We do unmapped page reclaim once here and once
    + * below, so that we don't lose out
    + */
    + reclaim_unmapped_pages(priority, zone, &sc);
    +
    if (!zone_watermark_ok_safe(zone, order,
    high_wmark_pages(zone), 0, 0)) {
    end_zone = i;
    @@ -2396,6 +2425,11 @@ loop_again:
    continue;

    sc.nr_scanned = 0;
    + /*
    + * Reclaim unmapped pages upfront, this should be
    + * really cheap
    + */
    + reclaim_unmapped_pages(priority, zone, &sc);

    /*
    * Call soft limit reclaim before calling shrink_zone.
    @@ -2715,7 +2749,8 @@ void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx)
    }
    if (!waitqueue_active(&pgdat->kswapd_wait))
    return;
    - if (zone_watermark_ok_safe(zone, order, low_wmark_pages(zone), 0, 0))
    + if (zone_watermark_ok_safe(zone, order, low_wmark_pages(zone), 0, 0) &&
    + !should_reclaim_unmapped_pages(zone))
    return;

    trace_mm_vmscan_wakeup_kswapd(pgdat->node_id, zone_idx(zone), order);
    @@ -2868,6 +2903,7 @@ static int __init kswapd_init(void)

    module_init(kswapd_init)

    +#if defined(CONFIG_UNMAPPED_PAGECACHE_CONTROL) || defined(CONFIG_NUMA)
    /*
    * Zone reclaim mode
    *
    @@ -2893,6 +2929,7 @@ int zone_reclaim_mode __read_mostly;
    * occur.
    */
    int sysctl_min_unmapped_ratio = 1;
    +int sysctl_max_unmapped_ratio = 16;

    /*
    * If the number of slab pages in a zone grows beyond this percentage then
    @@ -3088,6 +3125,54 @@ int zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)

    return ret;
    }
    +#endif
    +
    +#if defined(CONFIG_UNMAPPED_PAGECACHE_CONTROL)
    +/*
    + * Routine to reclaim unmapped pages, inspired from the code under
    + * CONFIG_NUMA that does unmapped page and slab page control by keeping
    + * min_unmapped_pages in the zone. We currently reclaim just unmapped
    + * pages, slab control will come in soon, at which point this routine
    + * should be called reclaim cached pages
    + */
    +unsigned long reclaim_unmapped_pages(int priority, struct zone *zone,
    + struct scan_control *sc)
    +{
    + if (unlikely(unmapped_page_control) &&
    + (zone_unmapped_file_pages(zone) > zone->min_unmapped_pages)) {
    + struct scan_control nsc;
    + unsigned long nr_pages;
    +
    + nsc = *sc;
    +
    + nsc.swappiness = 0;
    + nsc.may_writepage = 0;
    + nsc.may_unmap = 0;
    + nsc.nr_reclaimed = 0;
    +
    + nr_pages = zone_unmapped_file_pages(zone) -
    + zone->min_unmapped_pages;
    + /*
    + * We don't want to be too aggressive with our
    + * reclaim, it is our best effort to control
    + * unmapped pages
    + */
    + nr_pages >>= 3;
    +
    + zone_reclaim_pages(zone, &nsc, nr_pages);
    + return nsc.nr_reclaimed;
    + }
    + return 0;
    +}
    +
    +bool should_reclaim_unmapped_pages(struct zone *zone)
    +{
    + if (unlikely(unmapped_page_control) &&
    + (zone_unmapped_file_pages(zone) > zone->max_unmapped_pages))
    + return true;
    + return false;
    +}
    +#endif

    /*
    * page_evictable - test whether a page is evictable


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