Date:   Thu, 1 Sep 2022 14:03:36 +1200
From:   Barry Song <21cnbao@...il.com>
To:     SeongJae Park <sj@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, damon@...ts.linux.dev,
        linux-mm@...ck.org
Subject: Re: [PATCH 7/8] mm/damon: introduce DAMON-based LRU-lists Sorting

On Tue, Jun 14, 2022 at 10:01 AM SeongJae Park <sj@...nel.org> wrote:
>
> Users can do data access-aware LRU-lists sorting using 'LRU_PRIO' and
> 'LRU_DEPRIO' DAMOS actions.  However, finding best parameters including
> the hotness/coldness thresholds, CPU quota, and watermarks could be
> challenging for some users.  To make the scheme easy to be used without
> complex tuning for common situations, this commit implements a static
> kernel module called 'DAMON_LRU_SORT' using the 'LRU_PRIO' and
> 'LRU_DEPRIO' DAMOS actions.
>
> It proactively sorts LRU-lists using DAMON with conservatively chosen
> default values of the parameters.  That is, the module under its default
> parameters will make no harm for common situations but provide some
> level of efficiency improvements for systems having clear hot/cold
> access pattern under a level of memory pressure while consuming only a
> limited small portion of CPU time.

Hi SeongJae,
While I believe DAMON pro-active reclamation and LRU-SORT

>
> Signed-off-by: SeongJae Park <sj@...nel.org>
> ---
>  mm/damon/Kconfig    |   8 +
>  mm/damon/Makefile   |   1 +
>  mm/damon/lru_sort.c | 546 ++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 555 insertions(+)
>  create mode 100644 mm/damon/lru_sort.c
>
> diff --git a/mm/damon/Kconfig b/mm/damon/Kconfig
> index 9b559c76d6dd..66265e3a9c65 100644
> --- a/mm/damon/Kconfig
> +++ b/mm/damon/Kconfig
> @@ -92,4 +92,12 @@ config DAMON_RECLAIM
>           reclamation under light memory pressure, while the traditional page
>           scanning-based reclamation is used for heavy pressure.
>
> +config DAMON_LRU_SORT
> +       bool "Build DAMON-based LRU-lists sorting (DAMON_LRU_SORT)"
> +       depends on DAMON_PADDR
> +       help
> +         This builds the DAMON-based LRU-lists sorting subsystem.  It tries to
> +         protect frequently accessed (hot) pages while rarely accessed (cold)
> +         pages reclaimed first under memory pressure.
> +
>  endmenu
> diff --git a/mm/damon/Makefile b/mm/damon/Makefile
> index dbf7190b4144..3e6b8ad73858 100644
> --- a/mm/damon/Makefile
> +++ b/mm/damon/Makefile
> @@ -6,3 +6,4 @@ obj-$(CONFIG_DAMON_PADDR)       += ops-common.o paddr.o
>  obj-$(CONFIG_DAMON_SYSFS)      += sysfs.o
>  obj-$(CONFIG_DAMON_DBGFS)      += dbgfs.o
>  obj-$(CONFIG_DAMON_RECLAIM)    += reclaim.o
> +obj-$(CONFIG_DAMON_LRU_SORT)   += lru_sort.o
> diff --git a/mm/damon/lru_sort.c b/mm/damon/lru_sort.c
> new file mode 100644
> index 000000000000..c276736a071c
> --- /dev/null
> +++ b/mm/damon/lru_sort.c
> @@ -0,0 +1,546 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * DAMON-based LRU-lists Sorting
> + *
> + * Author: SeongJae Park <sj@...nel.org>
> + */
> +
> +#define pr_fmt(fmt) "damon-lru-sort: " fmt
> +
> +#include <linux/damon.h>
> +#include <linux/ioport.h>
> +#include <linux/module.h>
> +#include <linux/sched.h>
> +#include <linux/workqueue.h>
> +
> +#ifdef MODULE_PARAM_PREFIX
> +#undef MODULE_PARAM_PREFIX
> +#endif
> +#define MODULE_PARAM_PREFIX "damon_lru_sort."
> +
> +/*
> + * Enable or disable DAMON_LRU_SORT.
> + *
> + * You can enable DAMON_LRU_SORT by setting the value of this parameter as
> + * ``Y``.  Setting it as ``N`` disables DAMON_LRU_SORT.  Note that
> + * DAMON_LRU_SORT could do no real monitoring and LRU-lists sorting due to the
> + * watermarks-based activation condition.  Refer to below descriptions for the
> + * watermarks parameter for this.
> + */
> +static bool enabled __read_mostly;
> +
> +/*
> + * Make DAMON_LRU_SORT reads the input parameters again, except ``enabled``.
> + *
> + * Input parameters that updated while DAMON_LRU_SORT is running are not
> + * applied by default.  Once this parameter is set as ``Y``, DAMON_LRU_SORT
> + * reads values of parametrs except ``enabled`` again.  Once the re-reading is
> + * done, this parameter is set as ``N``.  If invalid parameters are found while
> + * the re-reading, DAMON_LRU_SORT will be disabled.
> + */
> +static bool commit_inputs __read_mostly;
> +module_param(commit_inputs, bool, 0600);
> +
> +/*
> + * Access frequency threshold for hot memory regions identification in permil.
> + *
> + * If a memory region is accessed in frequency of this or higher,
> + * DAMON_LRU_SORT identifies the region as hot, and mark it as accessed on the
> + * LRU list, so that it could not be reclaimed under memory pressure.  50% by
> + * default.
> + */
> +static unsigned long hot_thres_access_freq = 500;
> +module_param(hot_thres_access_freq, ulong, 0600);
> +
> +/*
> + * Time threshold for cold memory regions identification in microseconds.
> + *
> + * If a memory region is not accessed for this or longer time, DAMON_LRU_SORT
> + * identifies the region as cold, and mark it as unaccessed on the LRU list, so
> + * that it could be reclaimed first under memory pressure.  120 seconds by
> + * default.
> + */
> +static unsigned long cold_min_age __read_mostly = 120000000;
> +module_param(cold_min_age, ulong, 0600);
> +
> +/*
> + * Limit of time for trying the LRU lists sorting in milliseconds.
> + *
> + * DAMON_LRU_SORT tries to use only up to this time within a time window
> + * (quota_reset_interval_ms) for trying LRU lists sorting.  This can be used
> + * for limiting CPU consumption of DAMON_LRU_SORT.  If the value is zero, the
> + * limit is disabled.
> + *
> + * 10 ms by default.
> + */
> +static unsigned long quota_ms __read_mostly = 10;
> +module_param(quota_ms, ulong, 0600);
> +
> +/*
> + * The time quota charge reset interval in milliseconds.
> + *
> + * The charge reset interval for the quota of time (quota_ms).  That is,
> + * DAMON_LRU_SORT does not try LRU-lists sorting for more than quota_ms
> + * milliseconds or quota_sz bytes within quota_reset_interval_ms milliseconds.
> + *
> + * 1 second by default.
> + */
> +static unsigned long quota_reset_interval_ms __read_mostly = 1000;
> +module_param(quota_reset_interval_ms, ulong, 0600);
> +
> +/*
> + * The watermarks check time interval in microseconds.
> + *
> + * Minimal time to wait before checking the watermarks, when DAMON_LRU_SORT is
> + * enabled but inactive due to its watermarks rule.  5 seconds by default.
> + */
> +static unsigned long wmarks_interval __read_mostly = 5000000;
> +module_param(wmarks_interval, ulong, 0600);
> +
> +/*
> + * Free memory rate (per thousand) for the high watermark.
> + *
> + * If free memory of the system in bytes per thousand bytes is higher than
> + * this, DAMON_LRU_SORT becomes inactive, so it does nothing but periodically
> + * checks the watermarks.  200 (20%) by default.
> + */
> +static unsigned long wmarks_high __read_mostly = 200;
> +module_param(wmarks_high, ulong, 0600);
> +
> +/*
> + * Free memory rate (per thousand) for the middle watermark.
> + *
> + * If free memory of the system in bytes per thousand bytes is between this and
> + * the low watermark, DAMON_LRU_SORT becomes active, so starts the monitoring
> + * and the LRU-lists sorting.  150 (15%) by default.
> + */
> +static unsigned long wmarks_mid __read_mostly = 150;
> +module_param(wmarks_mid, ulong, 0600);
> +
> +/*
> + * Free memory rate (per thousand) for the low watermark.
> + *
> + * If free memory of the system in bytes per thousand bytes is lower than this,
> + * DAMON_LRU_SORT becomes inactive, so it does nothing but periodically checks
> + * the watermarks.  50 (5%) by default.
> + */
> +static unsigned long wmarks_low __read_mostly = 50;
> +module_param(wmarks_low, ulong, 0600);
> +
> +/*
> + * Sampling interval for the monitoring in microseconds.
> + *
> + * The sampling interval of DAMON for the hot/cold memory monitoring.  Please
> + * refer to the DAMON documentation for more detail.  5 ms by default.
> + */
> +static unsigned long sample_interval __read_mostly = 5000;
> +module_param(sample_interval, ulong, 0600);
> +
> +/*
> + * Aggregation interval for the monitoring in microseconds.
> + *
> + * The aggregation interval of DAMON for the hot/cold memory monitoring.
> + * Please refer to the DAMON documentation for more detail.  100 ms by default.
> + */
> +static unsigned long aggr_interval __read_mostly = 100000;
> +module_param(aggr_interval, ulong, 0600);
> +
> +/*
> + * Minimum number of monitoring regions.
> + *
> + * The minimal number of monitoring regions of DAMON for the hot/cold memory
> + * monitoring.  This can be used to set lower-bound of the monitoring quality.
> + * But, setting this too high could result in increased monitoring overhead.
> + * Please refer to the DAMON documentation for more detail.  10 by default.
> + */
> +static unsigned long min_nr_regions __read_mostly = 10;
> +module_param(min_nr_regions, ulong, 0600);
> +
> +/*
> + * Maximum number of monitoring regions.
> + *
> + * The maximum number of monitoring regions of DAMON for the hot/cold memory
> + * monitoring.  This can be used to set upper-bound of the monitoring overhead.
> + * However, setting this too low could result in bad monitoring quality.
> + * Please refer to the DAMON documentation for more detail.  1000 by default.
> + */
> +static unsigned long max_nr_regions __read_mostly = 1000;
> +module_param(max_nr_regions, ulong, 0600);
> +
> +/*
> + * Start of the target memory region in physical address.
> + *
> + * The start physical address of memory region that DAMON_LRU_SORT will do work
> + * against.  By default, biggest System RAM is used as the region.
> + */
> +static unsigned long monitor_region_start __read_mostly;
> +module_param(monitor_region_start, ulong, 0600);
> +
> +/*
> + * End of the target memory region in physical address.
> + *
> + * The end physical address of memory region that DAMON_LRU_SORT will do work
> + * against.  By default, biggest System RAM is used as the region.
> + */
> +static unsigned long monitor_region_end __read_mostly;
> +module_param(monitor_region_end, ulong, 0600);
> +
> +/*
> + * PID of the DAMON thread
> + *
> + * If DAMON_LRU_SORT is enabled, this becomes the PID of the worker thread.
> + * Else, -1.
> + */
> +static int kdamond_pid __read_mostly = -1;
> +module_param(kdamond_pid, int, 0400);
> +
> +/*
> + * Number of hot memory regions that tried to be LRU-sorted.
> + */
> +static unsigned long nr_lru_sort_tried_hot_regions __read_mostly;
> +module_param(nr_lru_sort_tried_hot_regions, ulong, 0400);
> +
> +/*
> + * Total bytes of hot memory regions that tried to be LRU-sorted.
> + */
> +static unsigned long bytes_lru_sort_tried_hot_regions __read_mostly;
> +module_param(bytes_lru_sort_tried_hot_regions, ulong, 0400);
> +
> +/*
> + * Number of hot memory regions that successfully be LRU-sorted.
> + */
> +static unsigned long nr_lru_sorted_hot_regions __read_mostly;
> +module_param(nr_lru_sorted_hot_regions, ulong, 0400);
> +
> +/*
> + * Total bytes of hot memory regions that successfully be LRU-sorted.
> + */
> +static unsigned long bytes_lru_sorted_hot_regions __read_mostly;
> +module_param(bytes_lru_sorted_hot_regions, ulong, 0400);
> +
> +/*
> + * Number of times that the time quota limit for hot regions have exceeded
> + */
> +static unsigned long nr_hot_quota_exceeds __read_mostly;
> +module_param(nr_hot_quota_exceeds, ulong, 0400);
> +
> +/*
> + * Number of cold memory regions that tried to be LRU-sorted.
> + */
> +static unsigned long nr_lru_sort_tried_cold_regions __read_mostly;
> +module_param(nr_lru_sort_tried_cold_regions, ulong, 0400);
> +
> +/*
> + * Total bytes of cold memory regions that tried to be LRU-sorted.
> + */
> +static unsigned long bytes_lru_sort_tried_cold_regions __read_mostly;
> +module_param(bytes_lru_sort_tried_cold_regions, ulong, 0400);
> +
> +/*
> + * Number of cold memory regions that successfully be LRU-sorted.
> + */
> +static unsigned long nr_lru_sorted_cold_regions __read_mostly;
> +module_param(nr_lru_sorted_cold_regions, ulong, 0400);
> +
> +/*
> + * Total bytes of cold memory regions that successfully be LRU-sorted.
> + */
> +static unsigned long bytes_lru_sorted_cold_regions __read_mostly;
> +module_param(bytes_lru_sorted_cold_regions, ulong, 0400);
> +
> +/*
> + * Number of times that the time quota limit for cold regions have exceeded
> + */
> +static unsigned long nr_cold_quota_exceeds __read_mostly;
> +module_param(nr_cold_quota_exceeds, ulong, 0400);
> +
> +static struct damon_ctx *ctx;
> +static struct damon_target *target;
> +
> +struct damon_lru_sort_ram_walk_arg {
> +       unsigned long start;
> +       unsigned long end;
> +};
> +
> +static int walk_system_ram(struct resource *res, void *arg)
> +{
> +       struct damon_lru_sort_ram_walk_arg *a = arg;
> +
> +       if (a->end - a->start < resource_size(res)) {
> +               a->start = res->start;
> +               a->end = res->end;
> +       }
> +       return 0;
> +}
> +
> +/*
> + * Find biggest 'System RAM' resource and store its start and end address in
> + * @start and @end, respectively.  If no System RAM is found, returns false.
> + */
> +static bool get_monitoring_region(unsigned long *start, unsigned long *end)
> +{
> +       struct damon_lru_sort_ram_walk_arg arg = {};
> +
> +       walk_system_ram_res(0, ULONG_MAX, &arg, walk_system_ram);
> +       if (arg.end <= arg.start)
> +               return false;
> +
> +       *start = arg.start;
> +       *end = arg.end;
> +       return true;
> +}
> +
> +/* Create a DAMON-based operation scheme for hot memory regions */
> +static struct damos *damon_lru_sort_new_hot_scheme(unsigned int hot_thres)
> +{
> +       struct damos_watermarks wmarks = {
> +               .metric = DAMOS_WMARK_FREE_MEM_RATE,
> +               .interval = wmarks_interval,
> +               .high = wmarks_high,
> +               .mid = wmarks_mid,
> +               .low = wmarks_low,
> +       };
> +       struct damos_quota quota = {
> +               /*
> +                * Do not try LRU-lists sorting of hot pages for more than half
> +                * of quota_ms milliseconds within quota_reset_interval_ms.
> +                */
> +               .ms = quota_ms / 2,
> +               .sz = 0,
> +               .reset_interval = quota_reset_interval_ms,
> +               /* Within the quota, mark hotter regions accessed first. */
> +               .weight_sz = 0,
> +               .weight_nr_accesses = 1,
> +               .weight_age = 0,
> +       };
> +       struct damos *scheme = damon_new_scheme(
> +                       /* Find regions having PAGE_SIZE or larger size */
> +                       PAGE_SIZE, ULONG_MAX,
> +                       /* and accessed for more than the threshold */
> +                       hot_thres, UINT_MAX,
> +                       /* no matter its age */
> +                       0, UINT_MAX,
> +                       /* prioritize those on LRU lists, as soon as found */
> +                       DAMOS_LRU_PRIO,
> +                       /* under the quota. */
> +                       &quota,
> +                       /* (De)activate this according to the watermarks. */
> +                       &wmarks);
> +
> +       return scheme;
> +}
> +
> +/* Create a DAMON-based operation scheme for cold memory regions */
> +static struct damos *damon_lru_sort_new_cold_scheme(unsigned int cold_thres)
> +{
> +       struct damos_watermarks wmarks = {
> +               .metric = DAMOS_WMARK_FREE_MEM_RATE,
> +               .interval = wmarks_interval,
> +               .high = wmarks_high,
> +               .mid = wmarks_mid,
> +               .low = wmarks_low,
> +       };
> +       struct damos_quota quota = {
> +               /*
> +                * Do not try LRU-lists sorting of cold pages for more than
> +                * half of quota_ms milliseconds within
> +                * quota_reset_interval_ms.
> +                */
> +               .ms = quota_ms / 2,
> +               .sz = 0,
> +               .reset_interval = quota_reset_interval_ms,
> +               /* Within the quota, mark colder regions not accessed first. */
> +               .weight_sz = 0,
> +               .weight_nr_accesses = 0,
> +               .weight_age = 1,
> +       };
> +       struct damos *scheme = damon_new_scheme(
> +                       /* Find regions having PAGE_SIZE or larger size */
> +                       PAGE_SIZE, ULONG_MAX,
> +                       /* and not accessed at all */
> +                       0, 0,
> +                       /* for cold_thres or more micro-seconds, and */
> +                       cold_thres, UINT_MAX,
> +                       /* mark those as not accessed, as soon as found */
> +                       DAMOS_LRU_DEPRIO,
> +                       /* under the quota. */
> +                       &quota,
> +                       /* (De)activate this according to the watermarks. */
> +                       &wmarks);
> +
> +       return scheme;
> +}
> +
> +static int damon_lru_sort_apply_parameters(void)
> +{
> +       struct damos *scheme, *next_scheme;
> +       struct damon_addr_range addr_range;
> +       unsigned int hot_thres, cold_thres;
> +       int err = 0;
> +
> +       err = damon_set_attrs(ctx, sample_interval, aggr_interval, 0,
> +                       min_nr_regions, max_nr_regions);
> +       if (err)
> +               return err;
> +
> +       /* free previously set schemes */
> +       damon_for_each_scheme_safe(scheme, next_scheme, ctx)
> +               damon_destroy_scheme(scheme);
> +
> +       /* aggr_interval / sample_interval is the maximum nr_accesses */
> +       hot_thres = aggr_interval / sample_interval * hot_thres_access_freq /
> +               1000;
> +       scheme = damon_lru_sort_new_hot_scheme(hot_thres);
> +       if (!scheme)
> +               return -ENOMEM;
> +       damon_add_scheme(ctx, scheme);
> +
> +       cold_thres = cold_min_age / aggr_interval;
> +       scheme = damon_lru_sort_new_cold_scheme(cold_thres);
> +       if (!scheme)
> +               return -ENOMEM;
> +       damon_add_scheme(ctx, scheme);
> +
> +       if (monitor_region_start > monitor_region_end)
> +               return -EINVAL;
> +       if (!monitor_region_start && !monitor_region_end &&
> +                       !get_monitoring_region(&monitor_region_start,
> +                               &monitor_region_end))
> +               return -EINVAL;
> +       addr_range.start = monitor_region_start;
> +       addr_range.end = monitor_region_end;
> +       return damon_set_regions(target, &addr_range, 1);
> +}
> +
> +static int damon_lru_sort_turn(bool on)
> +{
> +       int err;
> +
> +       if (!on) {
> +               err = damon_stop(&ctx, 1);
> +               if (!err)
> +                       kdamond_pid = -1;
> +               return err;
> +       }
> +
> +       err = damon_lru_sort_apply_parameters();
> +       if (err)
> +               return err;
> +
> +       err = damon_start(&ctx, 1, true);
> +       if (err)
> +               return err;
> +       kdamond_pid = ctx->kdamond->pid;
> +       return 0;
> +}
> +
> +static struct delayed_work damon_lru_sort_timer;
> +static void damon_lru_sort_timer_fn(struct work_struct *work)
> +{
> +       static bool last_enabled;
> +       bool now_enabled;
> +
> +       now_enabled = enabled;
> +       if (last_enabled != now_enabled) {
> +               if (!damon_lru_sort_turn(now_enabled))
> +                       last_enabled = now_enabled;
> +               else
> +                       enabled = last_enabled;
> +       }
> +}
> +static DECLARE_DELAYED_WORK(damon_lru_sort_timer, damon_lru_sort_timer_fn);
> +
> +static bool damon_lru_sort_initialized;
> +
> +static int damon_lru_sort_enabled_store(const char *val,
> +               const struct kernel_param *kp)
> +{
> +       int rc = param_set_bool(val, kp);
> +
> +       if (rc < 0)
> +               return rc;
> +
> +       if (!damon_lru_sort_initialized)
> +               return rc;
> +
> +       schedule_delayed_work(&damon_lru_sort_timer, 0);
> +
> +       return 0;
> +}
> +
> +static const struct kernel_param_ops enabled_param_ops = {
> +       .set = damon_lru_sort_enabled_store,
> +       .get = param_get_bool,
> +};
> +
> +module_param_cb(enabled, &enabled_param_ops, &enabled, 0600);
> +MODULE_PARM_DESC(enabled,
> +       "Enable or disable DAMON_LRU_SORT (default: disabled)");
> +
> +static int damon_lru_sort_handle_commit_inputs(void)
> +{
> +       int err;
> +
> +       if (!commit_inputs)
> +               return 0;
> +
> +       err = damon_lru_sort_apply_parameters();
> +       commit_inputs = false;
> +       return err;
> +}
> +
> +static int damon_lru_sort_after_aggregation(struct damon_ctx *c)
> +{
> +       struct damos *s;
> +
> +       /* update the stats parameter */
> +       damon_for_each_scheme(s, c) {
> +               if (s->action == DAMOS_LRU_PRIO) {
> +                       nr_lru_sort_tried_hot_regions = s->stat.nr_tried;
> +                       bytes_lru_sort_tried_hot_regions = s->stat.sz_tried;
> +                       nr_lru_sorted_hot_regions = s->stat.nr_applied;
> +                       bytes_lru_sorted_hot_regions = s->stat.sz_applied;
> +                       nr_hot_quota_exceeds = s->stat.qt_exceeds;
> +               } else if (s->action == DAMOS_LRU_DEPRIO) {
> +                       nr_lru_sort_tried_cold_regions = s->stat.nr_tried;
> +                       bytes_lru_sort_tried_cold_regions = s->stat.sz_tried;
> +                       nr_lru_sorted_cold_regions = s->stat.nr_applied;
> +                       bytes_lru_sorted_cold_regions = s->stat.sz_applied;
> +                       nr_cold_quota_exceeds = s->stat.qt_exceeds;
> +               }
> +       }
> +
> +       return damon_lru_sort_handle_commit_inputs();
> +}
> +
> +static int damon_lru_sort_after_wmarks_check(struct damon_ctx *c)
> +{
> +       return damon_lru_sort_handle_commit_inputs();
> +}
> +
> +static int __init damon_lru_sort_init(void)
> +{
> +       ctx = damon_new_ctx();
> +       if (!ctx)
> +               return -ENOMEM;
> +
> +       if (damon_select_ops(ctx, DAMON_OPS_PADDR))
> +               return -EINVAL;
> +
> +       ctx->callback.after_wmarks_check = damon_lru_sort_after_wmarks_check;
> +       ctx->callback.after_aggregation = damon_lru_sort_after_aggregation;
> +
> +       target = damon_new_target();
> +       if (!target) {
> +               damon_destroy_ctx(ctx);
> +               return -ENOMEM;
> +       }
> +       damon_add_target(ctx, target);
> +
> +       schedule_delayed_work(&damon_lru_sort_timer, 0);
> +
> +       damon_lru_sort_initialized = true;
> +       return 0;
> +}
> +
> +module_init(damon_lru_sort_init);
> --
> 2.25.1
>

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