Using shared memory to send data via nxt_port.

Usage:
    b = nxt_port_mmap_get_buf(task, port, size);
    b->mem.free = nxt_cpymem(b->mem.free, data, size);
    nxt_port_socket_write(task, port, NXT_PORT_MSG_DATA, -1, 0, b);

1 files changed, 700 insertions, 0 deletions

diff --git a/src/nxt_port_memory.c b/src/nxt_port_memory.c
new file mode 100644
index 00000000..447ef138
--- /dev/null
+++ b/src/nxt_port_memory.c
@@ -0,0 +1,700 @@
+
+#include <nxt_main.h>
+
+#if (NXT_HAVE_MEMFD_CREATE)
+
+#include <linux/memfd.h>
+#include <unistd.h>
+#include <sys/syscall.h>
+
+#endif
+
+#define PORT_MMAP_CHUNK_SIZE    (1024 * 16)
+#define PORT_MMAP_HEADER_SIZE   (1024 * 4)
+#define PORT_MMAP_SIZE          (PORT_MMAP_HEADER_SIZE + 1024 * 1024 * 10)
+
+#define PORT_MMAP_CHUNK_COUNT                                                 \
+    ( (PORT_MMAP_SIZE - PORT_MMAP_HEADER_SIZE) / PORT_MMAP_CHUNK_SIZE )
+
+
+typedef uint32_t  nxt_chunk_id_t;
+
+typedef nxt_atomic_uint_t  nxt_free_map_t;
+
+#define FREE_BITS (sizeof(nxt_free_map_t) * 8)
+
+#define FREE_IDX(nchunk) ((nchunk) / FREE_BITS)
+
+#define FREE_MASK(nchunk)                                                     \
+    ( 1ULL << ( (nchunk) % FREE_BITS ) )
+
+#define MAX_FREE_IDX FREE_IDX(PORT_MMAP_CHUNK_COUNT)
+
+
+/* Mapped at the start of shared memory segment. */
+struct nxt_port_mmap_header_s {
+    nxt_free_map_t  free_map[MAX_FREE_IDX];
+};
+
+
+/*
+ * Element of nxt_process_t.incoming/outgoing, shared memory segment
+ * descriptor.
+ */
+struct nxt_port_mmap_s {
+    uint32_t                    id;
+    nxt_fd_t                    fd;
+    nxt_pid_t                   pid; /* For sanity check. */
+    union {
+        void                    *mem;
+        nxt_port_mmap_header_t  *hdr;
+    } u;
+};
+
+
+/* Passed as a second iov chunk when 'mmap' bit in nxt_port_msg_t is 1. */
+typedef struct {
+    uint32_t            mmap_id;    /* Mmap index in nxt_process_t.outgoing. */
+    nxt_chunk_id_t      chunk_id;   /* Mmap chunk index. */
+    uint32_t            size;       /* Payload data size. */
+} nxt_port_mmap_msg_t;
+
+
+static nxt_bool_t
+nxt_port_mmap_get_free_chunk(nxt_port_mmap_t *port_mmap, nxt_chunk_id_t *c);
+
+#define nxt_port_mmap_get_chunk_busy(hdr, c)                                  \
+    ((hdr->free_map[FREE_IDX(c)] & FREE_MASK(c)) == 0)
+
+nxt_inline void
+nxt_port_mmap_set_chunk_busy(nxt_port_mmap_header_t *hdr, nxt_chunk_id_t c);
+
+nxt_inline void
+nxt_port_mmap_set_chunk_free(nxt_port_mmap_header_t *hdr, nxt_chunk_id_t c);
+
+#define nxt_port_mmap_chunk_id(port_mmap, b)                                  \
+    ((((u_char *) (b) - (u_char *) (port_mmap->u.mem)) -                      \
+        PORT_MMAP_HEADER_SIZE) / PORT_MMAP_CHUNK_SIZE)
+
+#define nxt_port_mmap_chunk_start(port_mmap, chunk)                           \
+    (((u_char *) (port_mmap->u.mem)) + PORT_MMAP_HEADER_SIZE +                \
+        (chunk) * PORT_MMAP_CHUNK_SIZE)
+
+
+void
+nxt_port_mmap_destroy(nxt_port_mmap_t *port_mmap)
+{
+    if (port_mmap->u.mem != NULL) {
+        nxt_mem_munmap(port_mmap->u.mem, PORT_MMAP_SIZE);
+        port_mmap->u.mem = NULL;
+    }
+
+    if (port_mmap->fd != -1) {
+        close(port_mmap->fd);
+        port_mmap->fd = -1;
+    }
+}
+
+
+static void
+nxt_port_mmap_buf_completion(nxt_task_t *task, void *obj, void *data)
+{
+    u_char                  *p;
+    nxt_buf_t               *b;
+    nxt_chunk_id_t          c;
+    nxt_mem_pool_t          *mp;
+    nxt_port_mmap_t         *port_mmap;
+    nxt_port_mmap_header_t  *hdr;
+
+    b = obj;
+
+    nxt_debug(task, "mmap buf completion: %p %p", b, b->mem.start);
+
+    mp = b->data;
+
+    port_mmap = (nxt_port_mmap_t *) b->parent;
+    hdr = port_mmap->u.hdr;
+
+    if (b->is_port_mmap_sent && b->mem.pos > b->mem.start) {
+        /*
+         * Chunks until b->mem.pos has been sent to other side,
+         * let's release rest (if any).
+         */
+        p = b->mem.pos - 1;
+        c = nxt_port_mmap_chunk_id(port_mmap, p) + 1;
+        p = nxt_port_mmap_chunk_start(port_mmap, c);
+    } else {
+        p = b->mem.start;
+        c = nxt_port_mmap_chunk_id(port_mmap, p);
+    }
+
+    while (p < b->mem.end) {
+        nxt_port_mmap_set_chunk_free(hdr, c);
+
+        p += PORT_MMAP_CHUNK_SIZE;
+        c++;
+    }
+
+    nxt_buf_free(mp, b);
+}
+
+
+static nxt_bool_t
+nxt_port_mmap_get_free_chunk(nxt_port_mmap_t *port_mmap, nxt_chunk_id_t *c)
+{
+    int             ffs;
+    size_t          i;
+    nxt_free_map_t  bits;
+    nxt_free_map_t  *free_map;
+
+    free_map = port_mmap->u.hdr->free_map;
+
+    for (i = 0; i < MAX_FREE_IDX; i++) {
+        bits = free_map[i];
+        if (bits == 0) {
+            continue;
+        }
+
+        ffs = __builtin_ffsll(bits);
+        if (ffs != 0) {
+            *c = i * FREE_BITS + ffs - 1;
+            return 1;
+        }
+    }
+
+    return 0;
+}
+
+
+nxt_inline void
+nxt_port_mmap_set_chunk_busy(nxt_port_mmap_header_t *hdr, nxt_chunk_id_t c)
+{
+    nxt_atomic_and_fetch(hdr->free_map + FREE_IDX(c), ~FREE_MASK(c));
+
+    nxt_thread_log_debug("set_chunk_busy: hdr %p; b %D", hdr, c);
+}
+
+
+nxt_inline void
+nxt_port_mmap_set_chunk_free(nxt_port_mmap_header_t *hdr, nxt_chunk_id_t c)
+{
+    nxt_atomic_or_fetch(hdr->free_map + FREE_IDX(c), FREE_MASK(c));
+
+    nxt_thread_log_debug("set_chunk_free: hdr %p; b %D", hdr, c);
+}
+
+
+nxt_port_mmap_t *
+nxt_port_incoming_port_mmap(nxt_task_t *task, nxt_process_t *process,
+    nxt_fd_t fd)
+{
+    struct stat      mmap_stat;
+    nxt_port_mmap_t  *port_mmap;
+
+    nxt_debug(task, "got new mmap fd #%FD from process %PI",
+              fd, process->pid);
+
+    if (fstat(fd, &mmap_stat) == -1) {
+        nxt_log(task, NXT_LOG_WARN, "fstat(%FD) failed %E", fd, nxt_errno);
+
+        return NULL;
+    }
+
+    if (process->incoming == NULL) {
+        process->incoming = nxt_array_create(process->mem_pool, 1,
+            sizeof(nxt_port_mmap_t));
+    }
+
+    if (nxt_slow_path(process->incoming == NULL)) {
+        nxt_log(task, NXT_LOG_WARN, "failed to allocate incoming array");
+
+        return NULL;
+    }
+
+    port_mmap = nxt_array_zero_add(process->incoming);
+    if (nxt_slow_path(port_mmap == NULL)) {
+        nxt_log(task, NXT_LOG_WARN, "failed to add mmap to incoming array");
+
+        return NULL;
+    }
+
+    port_mmap->id = process->incoming->nelts - 1;
+    port_mmap->fd = -1;
+    port_mmap->pid = process->pid;
+    port_mmap->u.mem = nxt_mem_mmap(NULL, mmap_stat.st_size,
+                                    PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
+
+    if (nxt_slow_path(port_mmap->u.mem == MAP_FAILED)) {
+        nxt_log(task, NXT_LOG_WARN, "mmap() failed %E", nxt_errno);
+
+        port_mmap->u.mem = NULL;
+
+        return NULL;
+    }
+
+    return port_mmap;
+}
+
+
+static void
+nxt_port_mmap_send_fd_buf_completion(nxt_task_t *task, void *obj, void *data)
+{
+    nxt_buf_t        *b;
+    nxt_port_t       *port;
+    nxt_port_mmap_t  *port_mmap;
+
+    b = obj;
+    port = b->data;
+    port_mmap = (nxt_port_mmap_t *) b->parent;
+
+    nxt_debug(task, "mmap fd %FD sent to %PI", port_mmap->fd, port->pid);
+
+    close(port_mmap->fd);
+    port_mmap->fd = -1;
+
+    nxt_buf_free(port->mem_pool, b);
+}
+
+
+static nxt_port_mmap_t *
+nxt_port_new_port_mmap(nxt_task_t *task, nxt_process_t *process,
+    nxt_port_t *port)
+{
+    u_char                  *p, name[64];
+    nxt_buf_t               *b;
+    nxt_port_mmap_t         *port_mmap;
+    nxt_port_mmap_header_t  *hdr;
+
+    if (process->outgoing == NULL) {
+        process->outgoing = nxt_array_create(process->mem_pool, 1,
+                                             sizeof(nxt_port_mmap_t));
+    }
+
+    if (nxt_slow_path(process->outgoing == NULL)) {
+        nxt_log(task, NXT_LOG_WARN, "failed to allocate outgoing array");
+
+        return NULL;
+    }
+
+    port_mmap = nxt_array_zero_add(process->outgoing);
+    if (nxt_slow_path(port_mmap == NULL)) {
+        nxt_log(task, NXT_LOG_WARN,
+                "failed to add port mmap to outgoing array");
+
+        return NULL;
+    }
+
+    port_mmap->id = process->outgoing->nelts - 1;
+    port_mmap->pid = process->pid;
+
+    p = nxt_sprintf(name, name + sizeof(name), "/nginext.%PI.%PT.%D",
+                    nxt_pid, task->thread->tid, nxt_random(&nxt_random_data));
+    *p = '\0';
+
+#if (NXT_HAVE_MEMFD_CREATE)
+    port_mmap->fd = syscall(SYS_memfd_create, name, MFD_CLOEXEC);
+
+    if (nxt_slow_path(port_mmap->fd == -1)) {
+        nxt_log(task, NXT_LOG_CRIT, "memfd_create(%s) failed %E",
+                name, nxt_errno);
+
+        goto remove_fail;
+    }
+
+    nxt_debug(task, "memfd_create(%s): %FD", name, port_mmap->fd);
+
+#elif (NXT_HAVE_SHM_OPEN)
+    shm_unlink((char *) name); // just in case
+
+    port_mmap->fd = shm_open((char *) name, O_CREAT | O_EXCL | O_RDWR,
+                             S_IRUSR | S_IWUSR);
+
+    nxt_debug(task, "shm_open(%s): %FD", name, port_mmap->fd);
+
+    if (nxt_slow_path(port_mmap->fd == -1)) {
+        nxt_log(task, NXT_LOG_CRIT, "shm_open(%s) failed %E", name, nxt_errno);
+
+        goto remove_fail;
+    }
+
+    if (nxt_slow_path(shm_unlink((char *) name) == -1)) {
+        nxt_log(task, NXT_LOG_WARN, "shm_unlink(%s) failed %E", name,
+                nxt_errno);
+    }
+#endif
+
+    if (nxt_slow_path(ftruncate(port_mmap->fd, PORT_MMAP_SIZE) == -1)) {
+        nxt_log(task, NXT_LOG_WARN, "ftruncate() failed %E", nxt_errno);
+
+        goto remove_fail;
+    }
+
+    port_mmap->u.mem = nxt_mem_mmap(NULL, PORT_MMAP_SIZE,
+                                    PROT_READ | PROT_WRITE, MAP_SHARED,
+                                    port_mmap->fd, 0);
+
+    if (nxt_slow_path(port_mmap->u.mem == MAP_FAILED)) {
+        goto remove_fail;
+    }
+
+    /* Init segment header. */
+    hdr = port_mmap->u.hdr;
+
+    nxt_memset(hdr->free_map, 0xFFU, sizeof(hdr->free_map));
+
+    /* Mark as busy chunk followed the last available chunk. */
+    nxt_port_mmap_set_chunk_busy(hdr, PORT_MMAP_CHUNK_COUNT);
+
+    nxt_debug(task, "send mmap fd %FD to process %PI", port_mmap->fd,
+              port->pid);
+
+    b = nxt_buf_mem_alloc(port->mem_pool, 0, 0);
+    b->completion_handler = nxt_port_mmap_send_fd_buf_completion;
+    b->data = port;
+    b->parent = port_mmap;
+
+    /* TODO handle error */
+    (void) nxt_port_socket_write(task, port, NXT_PORT_MSG_MMAP, port_mmap->fd,
+                                 0, 0, b);
+
+    nxt_log(task, NXT_LOG_DEBUG, "new mmap #%D created for %PI -> %PI",
+            port_mmap->id, nxt_pid, process->pid);
+
+    return port_mmap;
+
+remove_fail:
+
+    nxt_array_remove(process->outgoing, port_mmap);
+
+    return NULL;
+}
+
+
+static nxt_port_mmap_t *
+nxt_port_mmap_get(nxt_task_t *task, nxt_port_t *port, nxt_chunk_id_t *c,
+    size_t size)
+{
+    nxt_array_t      *outgoing;
+    nxt_process_t    *process;
+    nxt_port_mmap_t  *port_mmap;
+    nxt_port_mmap_t  *end_port_mmap;
+
+    process = nxt_runtime_process_get(task->thread->runtime, port->pid);
+    if (nxt_slow_path(process == NULL)) {
+        return NULL;
+    }
+
+    *c = 0;
+
+    if (process->outgoing == NULL) {
+        return nxt_port_new_port_mmap(task, process, port);
+    }
+
+    outgoing = process->outgoing;
+    port_mmap = outgoing->elts;
+    end_port_mmap = port_mmap + outgoing->nelts;
+
+    while (port_mmap < end_port_mmap) {
+
+        if (nxt_port_mmap_get_free_chunk(port_mmap, c)) {
+            return port_mmap;
+        }
+
+        port_mmap++;
+    }
+
+    /* TODO introduce port_mmap limit and release wait. */
+    return nxt_port_new_port_mmap(task, process, port);
+}
+
+
+static nxt_port_mmap_t *
+nxt_port_get_port_incoming_mmap(nxt_task_t *task, nxt_pid_t spid, uint32_t id)
+{
+    nxt_array_t      *incoming;
+    nxt_process_t    *process;
+    nxt_port_mmap_t  *port_mmap;
+
+    process = nxt_runtime_process_get(task->thread->runtime, spid);
+    if (nxt_slow_path(process == NULL)) {
+        return NULL;
+    }
+
+    incoming = process->incoming;
+    if (nxt_slow_path(incoming == NULL)) {
+        /* TODO add warning */
+        return NULL;
+    }
+
+    if (nxt_slow_path(incoming->nelts <= id)) {
+        /* TODO add warning */
+        return NULL;
+    }
+
+    port_mmap = incoming->elts;
+
+    return port_mmap + id;
+}
+
+
+nxt_buf_t *
+nxt_port_mmap_get_buf(nxt_task_t *task, nxt_port_t *port, size_t size)
+{
+    size_t                  nchunks;
+    nxt_buf_t               *b;
+    nxt_chunk_id_t          c;
+    nxt_port_mmap_t         *port_mmap;
+    nxt_port_mmap_header_t  *hdr;
+
+    nxt_debug(task, "request %z bytes shm buffer", size);
+
+    b = nxt_mem_cache_zalloc0(port->mem_pool, NXT_BUF_PORT_MMAP_SIZE);
+    if (nxt_slow_path(b == NULL)) {
+        return NULL;
+    }
+
+    b->data = port->mem_pool;
+    b->completion_handler = nxt_port_mmap_buf_completion;
+    b->size = NXT_BUF_PORT_MMAP_SIZE;
+
+    nxt_buf_set_port_mmap(b);
+
+    port_mmap = nxt_port_mmap_get(task, port, &c, size);
+    if (nxt_slow_path(port_mmap == NULL)) {
+        nxt_buf_free(port->mem_pool, b);
+        return NULL;
+    }
+
+    hdr = port_mmap->u.hdr;
+
+    b->parent = port_mmap;
+    b->mem.start = nxt_port_mmap_chunk_start(port_mmap, c);
+    b->mem.pos = b->mem.start;
+    b->mem.free = b->mem.start;
+    b->mem.end = b->mem.start + PORT_MMAP_CHUNK_SIZE;
+
+    nxt_port_mmap_set_chunk_busy(hdr, c);
+
+    nchunks = size / PORT_MMAP_CHUNK_SIZE;
+    if ((size % PORT_MMAP_CHUNK_SIZE) != 0 || nchunks == 0) {
+        nchunks++;
+    }
+
+    c++;
+    nchunks--;
+
+    /* Try to acquire as much chunks as required. */
+    while (nchunks > 0) {
+
+        if (nxt_port_mmap_get_chunk_busy(hdr, c)) {
+            break;
+        }
+        nxt_port_mmap_set_chunk_busy(hdr, c);
+
+        b->mem.end += PORT_MMAP_CHUNK_SIZE;
+        c++;
+        nchunks--;
+    }
+
+    return b;
+}
+
+
+static nxt_buf_t *
+nxt_port_mmap_get_incoming_buf(nxt_task_t *task, nxt_port_t *port,
+    nxt_pid_t spid, nxt_port_mmap_msg_t *mmap_msg)
+{
+    size_t                  nchunks;
+    nxt_buf_t               *b;
+    nxt_port_mmap_t         *port_mmap;
+
+    b = nxt_mem_cache_zalloc0(port->mem_pool, NXT_BUF_PORT_MMAP_SIZE);
+    if (nxt_slow_path(b == NULL)) {
+        return NULL;
+    }
+
+    b->data = port->mem_pool;
+    b->completion_handler = nxt_port_mmap_buf_completion;
+    b->size = NXT_BUF_PORT_MMAP_SIZE;
+
+    nxt_buf_set_port_mmap(b);
+
+    port_mmap = nxt_port_get_port_incoming_mmap(task, spid, mmap_msg->mmap_id);
+    if (nxt_slow_path(port_mmap == NULL)) {
+        nxt_buf_free(port->mem_pool, b);
+        return NULL;
+    }
+
+    nchunks = mmap_msg->size / PORT_MMAP_CHUNK_SIZE;
+    if ((mmap_msg->size % PORT_MMAP_CHUNK_SIZE) != 0) {
+        nchunks++;
+    }
+
+    b->mem.start = nxt_port_mmap_chunk_start(port_mmap, mmap_msg->chunk_id);
+    b->mem.pos = b->mem.start;
+    b->mem.free = b->mem.start + mmap_msg->size;
+    b->mem.end = b->mem.start + nchunks * PORT_MMAP_CHUNK_SIZE;
+
+    b->parent = port_mmap;
+
+    return b;
+}
+
+
+void
+nxt_port_mmap_write(nxt_task_t *task, nxt_port_t *port,
+    nxt_port_send_msg_t *msg, nxt_sendbuf_coalesce_t *sb)
+{
+    size_t               bsize;
+    nxt_buf_t            *b, *bmem;
+    nxt_uint_t           i;
+    nxt_port_mmap_t      *port_mmap;
+    nxt_port_mmap_msg_t  *mmap_msg;
+
+    nxt_debug(task, "prepare %z bytes message for transfer to process %PI "
+              "via shared memory", sb->size, port->pid);
+
+    bsize = sb->niov * sizeof(nxt_port_mmap_msg_t);
+
+    b = nxt_buf_mem_alloc(port->mem_pool, bsize, 0);
+    if (nxt_slow_path(b == NULL)) {
+        return;
+    }
+
+    mmap_msg = (nxt_port_mmap_msg_t *) b->mem.start;
+    bmem = msg->buf;
+
+    for (i = 0; i < sb->niov; i++, mmap_msg++) {
+
+        /* Lookup buffer which starts current iov_base. */
+        while (bmem && sb->iobuf[i].iov_base != bmem->mem.pos) {
+            bmem = bmem->next;
+        }
+
+        if (nxt_slow_path(bmem == NULL)) {
+            nxt_log_error(NXT_LOG_ERR, task->log, "failed to find buf for "
+                          "iobuf[%d]", i);
+            return;
+            /* TODO clear b and exit */
+        }
+
+        port_mmap = (nxt_port_mmap_t *) bmem->parent;
+
+        mmap_msg->mmap_id = port_mmap->id;
+        mmap_msg->chunk_id = nxt_port_mmap_chunk_id(port_mmap, bmem->mem.pos);
+        mmap_msg->size = sb->iobuf[i].iov_len;
+
+        nxt_debug(task, "mmap_msg={%D, %D, %D} to %PI",
+                  mmap_msg->mmap_id, mmap_msg->chunk_id, mmap_msg->size,
+                  port->pid);
+    }
+
+    msg->buf = b;
+    b->mem.free += bsize;
+
+    sb->iobuf[0].iov_base = b->mem.pos;
+    sb->iobuf[0].iov_len = bsize;
+    sb->niov = 1;
+    sb->size = bsize;
+
+    msg->port_msg.mmap = 1;
+}
+
+
+void
+nxt_port_mmap_read(nxt_task_t *task, nxt_port_t *port,
+    nxt_port_recv_msg_t *msg, size_t size)
+{
+    nxt_buf_t            *b, **pb;
+    nxt_port_mmap_msg_t  *end, *mmap_msg;
+
+    b = msg->buf;
+
+    mmap_msg = (nxt_port_mmap_msg_t *) b->mem.pos;
+    end = (nxt_port_mmap_msg_t *) b->mem.free;
+
+    pb = &msg->buf;
+
+    while (mmap_msg < end) {
+        nxt_debug(task, "mmap_msg={%D, %D, %D} from %PI",
+                  mmap_msg->mmap_id, mmap_msg->chunk_id, mmap_msg->size,
+                  msg->port_msg.pid);
+
+        *pb = nxt_port_mmap_get_incoming_buf(task, port, msg->port_msg.pid,
+                                             mmap_msg);
+        if (nxt_slow_path(*pb == NULL)) {
+            nxt_log_error(NXT_LOG_ERR, task->log, "failed to get mmap buffer");
+
+            break;
+        }
+
+        pb = &(*pb)->next;
+        mmap_msg++;
+    }
+
+    /* Mark original buf as complete. */
+    b->mem.pos += nxt_buf_used_size(b);
+}
+
+
+nxt_port_method_t
+nxt_port_mmap_get_method(nxt_task_t *task, nxt_port_t *port, nxt_buf_t *b)
+{
+    nxt_port_mmap_t    *port_mmap;
+    nxt_port_method_t  m;
+
+    m = NXT_PORT_METHOD_ANY;
+
+    for (; b != NULL; b = b->next) {
+        if (nxt_buf_used_size(b) == 0) {
+            /* empty buffers does not affect method */
+            continue;
+        }
+
+        if (nxt_buf_is_port_mmap(b)) {
+            port_mmap = (nxt_port_mmap_t *) b->parent;
+
+            if (m == NXT_PORT_METHOD_PLAIN) {
+                nxt_log_error(NXT_LOG_ERR, task->log,
+                              "mixing plain and mmap buffers, "
+                              "using plain mode");
+
+                break;
+            }
+
+            if (port->pid != port_mmap->pid) {
+                nxt_log_error(NXT_LOG_ERR, task->log,
+                              "send mmap buffer for %PI to %PI, "
+                              "using plain mode", port_mmap->pid, port->pid);
+
+                m = NXT_PORT_METHOD_PLAIN;
+
+                break;
+            }
+
+            if (m == NXT_PORT_METHOD_ANY) {
+                nxt_debug(task, "using mmap mode");
+
+                m = NXT_PORT_METHOD_MMAP;
+            }
+        } else {
+            if (m == NXT_PORT_METHOD_MMAP) {
+                nxt_log_error(NXT_LOG_ERR, task->log,
+                              "mixing mmap and plain buffers, "
+                              "switching to plain mode");
+
+                m = NXT_PORT_METHOD_PLAIN;
+
+                break;
+            }
+
+            if (m == NXT_PORT_METHOD_ANY) {
+                nxt_debug(task, "using plain mode");
+
+                m = NXT_PORT_METHOD_PLAIN;
+            }
+        }
+    }
+
+    return m;
+}