// ss_release_policy_box.c - SuperSlab Release Policy Box Implementation
#include "ss_release_policy_box.h"
#include "ss_mem_lean_env_box.h"
#include "madvise_guard_box.h"
#include "ss_os_acquire_box.h"
#include "../superslab/superslab_types.h"
#include <sys/mman.h>
#include <errno.h>

// ============================================================================
// Release Policy Implementation
// ============================================================================

bool ss_should_keep_superslab(SuperSlab* ss, int class_idx) {
    (void)ss;        // Reserved for future budget logic
    (void)class_idx; // Reserved for per-class policy

    // In lean mode: allow release of empty superslabs
    // In FAST mode (default): keep all superslabs (persistent backend)
    if (ss_mem_lean_enabled()) {
        // TODO: Add per-class budget logic here if needed
        // For now: allow release (caller decides based on empty state)
        return false;  // Signal: OK to release in lean mode
    }

    // Default (FAST mode): keep all superslabs (speed-first)
    return true;
}

int ss_maybe_decommit_superslab(void* ptr, size_t size) {
    // Fast path: lean mode disabled → no-op
    if (!ss_mem_lean_enabled()) {
        return 0;
    }

    // Get decommit mode from ENV
    ss_mem_lean_decommit_mode_t mode = ss_mem_lean_decommit_mode();

    // If decommit is OFF, skip (only prewarm suppression active)
    if (mode == SS_MEM_LEAN_DECOMMIT_OFF) {
        return 0;
    }

    // Select madvise advice based on mode
    int advice;
    switch (mode) {
        case SS_MEM_LEAN_DECOMMIT_FREE:
#ifdef MADV_FREE
            advice = MADV_FREE;  // Lazy reclaim (fast, kernel 4.5+)
#else
            // Fallback to MADV_DONTNEED if MADV_FREE not available
            advice = MADV_DONTNEED;
#endif
            break;

        case SS_MEM_LEAN_DECOMMIT_DONTNEED:
            advice = MADV_DONTNEED;  // Eager reclaim (slower, but universal)
            break;

        default:
            return 0;  // Unknown mode, skip
    }

    // Call DSO-guarded madvise (respects guard rules)
    // This will:
    //   - Skip if ptr overlaps DSO (.fini_array safety)
    //   - Disable future calls on ENOMEM (fail-fast)
    //   - Update madvise counters
    int ret = ss_os_madvise_guarded(ptr, size, advice, "ss_release_policy_decommit");

    if (ret == 0) {
        // Success: update lean_decommit counter
        ss_os_stats_record_lean_decommit();
    }

    return ret;
}