extstore: C version of automove algorithm

couple TODO items left for a new issue I thought of. Also hardcoded memory
buffer size which should be fixed.

also need to change the "free and re-init" logic to use a boolean in case any
related option changes.

1 files changed, 259 insertions, 0 deletions

diff --git a/slab_automove_extstore.c b/slab_automove_extstore.c
new file mode 100644
index 0000000..ce08bbe
--- /dev/null
+++ b/slab_automove_extstore.c
@@ -0,0 +1,259 @@
+/*  Copyright 2017 Facebook.
+ *
+ *  Use and distribution licensed under the BSD license.  See
+ *  the LICENSE file for full text.
+ */
+
+/* -*- Mode: C; tab-width: 4; c-basic-offset: 4; indent-tabs-mode: nil -*- */
+#include "memcached.h"
+#include "slab_automove_extstore.h"
+#include <stdlib.h>
+#include <string.h>
+
+#define MIN_PAGES_FOR_SOURCE 2
+#define MIN_PAGES_FOR_RECLAIM 2.5
+#define MIN_PAGES_FREE 1.5
+#define MEMCHECK_PERIOD 60
+
+struct window_data {
+    uint64_t age;
+    uint64_t dirty;
+    uint64_t evicted;
+    unsigned int excess_free;
+};
+
+struct window_global {
+    uint32_t pool_low;
+    uint32_t pool_high;
+};
+
+typedef struct {
+    struct window_data *window_data;
+    struct window_global *window_global;
+    struct settings *settings;
+    uint32_t window_size;
+    uint32_t window_cur;
+    uint32_t item_size;
+    rel_time_t last_memcheck_run;
+    double max_age_ratio;
+    double free_ratio;
+    unsigned int free_mem[MAX_NUMBER_OF_SLAB_CLASSES];
+    item_stats_automove iam_before[MAX_NUMBER_OF_SLAB_CLASSES];
+    item_stats_automove iam_after[MAX_NUMBER_OF_SLAB_CLASSES];
+    slab_stats_automove sam_before[MAX_NUMBER_OF_SLAB_CLASSES];
+    slab_stats_automove sam_after[MAX_NUMBER_OF_SLAB_CLASSES];
+} slab_automove;
+
+void *slab_automove_extstore_init(struct settings *settings) {
+    uint32_t window_size = settings->slab_automove_window;
+    double max_age_ratio = settings->slab_automove_ratio;
+    slab_automove *a = calloc(1, sizeof(slab_automove));
+    if (a == NULL)
+        return NULL;
+    a->window_data = calloc(window_size * MAX_NUMBER_OF_SLAB_CLASSES, sizeof(struct window_data));
+    a->window_global = calloc(window_size, sizeof(struct window_global));
+    a->window_size = window_size;
+    a->max_age_ratio = max_age_ratio;
+    a->free_ratio = settings->slab_automove_freeratio;
+    a->item_size = settings->ext_item_size;
+    a->last_memcheck_run = 0;
+    a->settings = settings;
+    if (a->window_data == NULL || a->window_global == NULL) {
+        if (a->window_data)
+            free(a->window_data);
+        if (a->window_global)
+            free(a->window_global);
+        free(a);
+        return NULL;
+    }
+
+    // do a dry run to fill the before structs
+    fill_item_stats_automove(a->iam_before);
+    fill_slab_stats_automove(a->sam_before);
+
+    return (void *)a;
+}
+
+void slab_automove_extstore_free(void *arg) {
+    slab_automove *a = (slab_automove *)arg;
+    free(a->window_data);
+    free(a);
+}
+
+static void window_sum(struct window_data *wd, struct window_data *w,
+        uint32_t size) {
+    for (int x = 0; x < size; x++) {
+        struct window_data *d = &wd[x];
+        w->age += d->age;
+        w->dirty += d->dirty;
+        w->evicted += d->evicted;
+        w->excess_free += d->excess_free;
+    }
+}
+
+/* This could potentially merge with above */
+static void window_global_sum(struct window_global *wg,
+        struct window_global *w, uint32_t size) {
+    for (int x = 0; x < size; x++) {
+        struct window_global *d = &wg[x];
+        w->pool_high += d->pool_high;
+        w->pool_low += d->pool_low;
+    }
+}
+
+static void global_pool_check(slab_automove *a) {
+    bool mem_limit_reached;
+    uint32_t free = a->free_mem[0];
+    struct window_global *wg = &a->window_global[a->window_cur % a->window_size];
+    unsigned int count = global_page_pool_size(&mem_limit_reached);
+    memset(wg, 0, sizeof(struct window_global));
+    if (!mem_limit_reached)
+        return;
+    if (count < free / 2) {
+        wg->pool_low = 1;
+    } else if (count > free) {
+        wg->pool_high = 1;
+    }
+}
+
+static void memcheck(slab_automove *a) {
+    unsigned int total_pages = 0;
+    if (current_time < a->last_memcheck_run + MEMCHECK_PERIOD)
+        return;
+    a->last_memcheck_run = current_time;
+    for (int n = 1; n < MAX_NUMBER_OF_SLAB_CLASSES; n++) {
+        slab_stats_automove *sam = &a->sam_after[n];
+        total_pages += sam->total_pages;
+        unsigned int hold_free = (sam->total_pages * sam->chunks_per_page)
+            * a->free_ratio;
+        if (sam->chunks_per_page * MIN_PAGES_FREE > hold_free)
+            hold_free = sam->chunks_per_page * MIN_PAGES_FREE;
+        a->free_mem[n] = hold_free;
+        if (a->settings->ext_free_memchunks[n] != hold_free) {
+            a->settings->ext_free_memchunks[n] = hold_free;
+        }
+    }
+    a->free_mem[0] = total_pages * a->free_ratio;
+}
+
+void slab_automove_extstore_run(void *arg, int *src, int *dst) {
+    slab_automove *a = (slab_automove *)arg;
+    int n;
+    struct window_data w_sum;
+    int oldest = -1;
+    uint64_t oldest_age = 0;
+    int youngest = -1;
+    uint64_t youngest_age = ~0;
+    *src = -1;
+    *dst = -1;
+
+    global_pool_check(a);
+    struct window_global wg_sum;
+    memset(&wg_sum, 0, sizeof(struct window_global));
+    window_global_sum(a->window_global, &wg_sum, a->window_size);
+    // fill after structs
+    fill_item_stats_automove(a->iam_after);
+    fill_slab_stats_automove(a->sam_after);
+    a->window_cur++;
+
+    memcheck(a);
+
+    // iterate slabs
+    for (n = POWER_SMALLEST; n < MAX_NUMBER_OF_SLAB_CLASSES; n++) {
+        bool small_slab = a->sam_before[n].chunk_size < a->item_size
+            ? true : false;
+        int w_offset = n * a->window_size;
+        struct window_data *wd = &a->window_data[w_offset + (a->window_cur % a->window_size)];
+        // summarize the window-up-to-now.
+        memset(&w_sum, 0, sizeof(struct window_data));
+        window_sum(&a->window_data[w_offset], &w_sum, a->window_size);
+        memset(wd, 0, sizeof(struct window_data));
+
+        // if page delta, or evicted delta, mark window dirty
+        // (or outofmemory)
+        if (a->iam_after[n].evicted - a->iam_before[n].evicted > 0 ||
+            a->iam_after[n].outofmemory - a->iam_before[n].outofmemory > 0) {
+            wd->evicted = 1;
+            wd->dirty = 1;
+        }
+        if (a->sam_after[n].total_pages - a->sam_before[n].total_pages > 0) {
+            wd->dirty = 1;
+        }
+        // Mark excess free if we're over the free mem limit and the number of
+        // chunks aren't decreasing at all.
+        if (a->sam_after[n].free_chunks > a->free_mem[n]
+                && a->sam_after[n].free_chunks - a->sam_before[n].free_chunks >= 0) {
+            if (a->free_mem[n] > 0) {
+                wd->excess_free = 1;
+            }
+        }
+
+        // set age into window
+        wd->age = a->iam_after[n].age;
+
+        // grab age as average of window total
+        uint64_t age = w_sum.age / a->window_size;
+
+        // if > N free chunks and not dirty, make decision.
+        if (a->sam_after[n].free_chunks > a->sam_after[n].chunks_per_page * MIN_PAGES_FOR_RECLAIM) {
+            if (small_slab && w_sum.dirty == 0) {
+                *src = n;
+                *dst = 0;
+                break;
+            } else if (!small_slab && w_sum.excess_free >= a->window_size / 2
+                    && a->sam_after[n].total_pages > MIN_PAGES_FOR_SOURCE) {
+                // If large slab and free chunks haven't decreased for a full
+                // window, reclaim pages.
+                *src = n;
+                *dst = 0;
+            }
+        }
+
+        // if oldest and have enough pages, is oldest
+        if (!small_slab
+                && age > oldest_age
+                && a->sam_after[n].total_pages > MIN_PAGES_FOR_SOURCE) {
+            oldest = n;
+            oldest_age = age;
+        }
+
+        // don't count as youngest if it hasn't been using new chunks.
+        if (!small_slab && age < youngest_age && a->sam_after[n].total_pages != 0
+                && w_sum.excess_free < a->window_size) {
+            youngest = n;
+            youngest_age = age;
+        }
+    }
+
+    memcpy(a->iam_before, a->iam_after,
+            sizeof(item_stats_automove) * MAX_NUMBER_OF_SLAB_CLASSES);
+    memcpy(a->sam_before, a->sam_after,
+            sizeof(slab_stats_automove) * MAX_NUMBER_OF_SLAB_CLASSES);
+    // only make decisions if window has filled once.
+    if (a->window_cur < a->window_size)
+        return;
+
+    if (wg_sum.pool_high && youngest != -1) {
+        /**src = 0;
+        *dst = youngest;*/
+        /* TODO: No current way to directly assign page from 0 to elsewhere.
+         * Do a current hack by setting the youngest's free mem limiter to
+         * zero and re-running memcheck in the next second.
+         * If set rates are very high and the pool is too low, this can bottom
+         * out...
+         */
+        a->last_memcheck_run = 0;
+        a->settings->ext_free_memchunks[youngest] = 0;
+    } else if (wg_sum.pool_low && oldest != -1) {
+        *src = oldest;
+        *dst = 0;
+    } else if (youngest != -1 && oldest != -1 && youngest != oldest) {
+        // if we have a youngest and oldest, and oldest is outside the ratio.
+        if (a->sam_after[youngest].free_chunks <= a->free_mem[youngest]
+                && youngest_age < ((double)oldest_age * a->max_age_ratio)) {
+            *src = oldest;
+            *dst = youngest;
+        }
+    }
+    return;
+}