nt-lite/code/user/tests/pcache_pressure/pcache_pressure.c

// Sequential file-cache pressure test.
// Reads this test executable through SysReadFile and checks cache behavior when
// the image is large enough to apply pressure.

#include <stdint.h>
#include <stddef.h>
#include <string.h>
#include <ntlite/syscall.h>

#define READ_CHUNK 4096u
#define MIN_PRESSURE_BYTES (3u * 1024u * 1024u)
#define RESIDENT_LIMIT_PAGES 640u

static uint8_t gBuf[READ_CHUNK];

static void print(const char* s) {
    SYS_WRITE_CONSOLE_REQUEST req = { SysSvFromCstr(s) };
    SysWriteConsole(&req);
}

static void print_u64(uint64_t v) {
    char buf[32];
    int i = 0;
    if (v == 0) { print("0"); return; }
    while (v && i < (int)sizeof(buf)) {
        buf[i++] = (char)('0' + (v % 10));
        v /= 10;
    }
    while (i--) {
        char c[2] = { buf[i], 0 };
        print(c);
    }
}

static void exit_now(int code) {
    while (true) SysExitProcess(code);
}

static void fail(const char* msg) {
    print("pcache_pressure: ");
    print(msg);
    print("\n");
    exit_now(1);
}

static void fail_status(const char* what, uint32_t status) {
    print("pcache_pressure: ");
    print(what);
    print(" failed status=");
    print_u64(status);
    print("\n");
    exit_now(1);
}

static uint32_t query_cache(SYS_FILE_CACHE_STATS* out) {
    return SysQueryKernelStats(SYS_KERNEL_STATS_FILE_CACHE, out, sizeof(*out), 0);
}

static char gSelfPath[SYS_PATH_MAX];

// Copies a string view into a fixed NUL-terminated buffer.
static int copy_view(char* out, size_t outSize, SYS_STRING_VIEW view) {
    if (!out || outSize == 0 || !view.Data || view.Length + 1 > outSize)
        return 0;
    memcpy(out, view.Data, view.Length);
    out[view.Length] = '\0';
    return 1;
}

// Opens this process image as the cache-pressure input file.
static uint32_t open_self_image(uint32_t* fileOut, const char** pathOut, uint64_t* sizeOut) {
    SYS_PEB* peb = SysGetPeb();
    if (!peb || peb->Magic != SYS_PEB_MAGIC || peb->Version != SYS_ENV_VERSION)
        return NTLSTATUS_INVALID_PARAMETER;
    if (!copy_view(gSelfPath, sizeof(gSelfPath), peb->ImagePath))
        return NTLSTATUS_INVALID_PARAMETER;

    uint32_t h = 0;
    SYS_OPEN_FILE_REQUEST req = SysMakeOpenFileRequest(SysSvFromCstr(gSelfPath),
                                                       SYS_FILE_ACCESS_READ | SYS_FILE_ACCESS_QUERY,
                                                       SYS_FILE_OPEN_EXISTING,
                                                       SYS_FILE_FLAG_NONE,
                                                       &h);
    uint32_t s = SysOpenFile(&req);
    if (s != NTLSTATUS_SUCCESS)
        return s;

    uint64_t size = 0;
    s = SysGetFileSize(h, &size);
    if (s != NTLSTATUS_SUCCESS) {
        SysCloseHandle(h);
        return s;
    }
    if (size == 0) {
        SysCloseHandle(h);
        return NTLSTATUS_NOT_FOUND;
    }

    *fileOut = h;
    *pathOut = gSelfPath;
    *sizeOut = size;
    return NTLSTATUS_SUCCESS;
}

int main(void) {
    print("pcache_pressure: start\n");

    SYS_FILE_CACHE_STATS before;
    SYS_FILE_CACHE_STATS after;
    if (query_cache(&before) != NTLSTATUS_SUCCESS)
        fail("initial cache stats query failed");

    uint32_t file = 0;
    const char* path = 0;
    uint64_t size = 0;
    uint32_t s = open_self_image(&file, &path, &size);
    if (s != NTLSTATUS_SUCCESS)
        fail_status("open self image", s);

    print("pcache_pressure: using ");
    print(path ? path : "<unknown>");
    print(" size=");
    print_u64(size);
    print("\n");

    uint64_t total = 0;
    uint64_t target = size < (8u * 1024u * 1024u) ? size : (8u * 1024u * 1024u);
    while (total < target) {
        size_t got = 0;
        SYS_FILE_IO_REQUEST readReq = SysMakeFileIoRequest(file, gBuf, sizeof(gBuf), &got);
        s = SysReadFile(&readReq);
        if (s != NTLSTATUS_SUCCESS)
            fail_status("read", s);
        if (got == 0)
            break;
        total += got;
    }

    SysCloseHandle(file);

    if (total == 0)
        fail("self image read returned no bytes");

    if (query_cache(&after) != NTLSTATUS_SUCCESS)
        fail("final cache stats query failed");

    uint64_t loads = after.Loads - before.Loads;
    uint64_t hits  = after.Hits  - before.Hits;
    uint64_t drops = after.Drops - before.Drops;

    print("pcache_pressure: read bytes="); print_u64(total);
    print(" loads+="); print_u64(loads);
    print(" hits+="); print_u64(hits);
    print(" drops+="); print_u64(drops);
    print(" resident="); print_u64(after.ResidentPages);
    print(" active="); print_u64(after.ActivePages);
    print(" standby="); print_u64(after.StandbyPages);
    print(" max="); print_u64(after.MaxResidentPages);
    print("\n");

    if (size >= MIN_PRESSURE_BYTES) {
        if (loads < 512)
            fail("expected at least 512 cache page loads");
        if (after.ResidentPages > RESIDENT_LIMIT_PAGES)
            fail("resident page cache exceeded pressure bound");
        if (loads > RESIDENT_LIMIT_PAGES && drops == 0)
            fail("cache did not drop clean pages under pressure");
    } else {
        print("pcache_pressure: self image below pressure size; pressure bounds skipped\n");
    }

    print("pcache_pressure: PASS\n");
    exit_now(0);
    return 0;
}