bus: reduce calls to KDBUS_CMD_MEMFD_SIZE_SET ioctl

Instead of calling it for each buffer append, increase allocation
exponentially and set the real value only at the end, when sealing off
the memfd.

This should drastically reduce the number of times we invoke the
ioctl().

1 files changed, 22 insertions, 17 deletions

diff --git a/src/libsystemd-bus/bus-kernel.c b/src/libsystemd-bus/bus-kernel.c
index bd6b84a7ba..7d514616a4 100644
--- a/src/libsystemd-bus/bus-kernel.c
+++ b/src/libsystemd-bus/bus-kernel.c
@@ -919,12 +919,13 @@ int bus_kernel_read_message(sd_bus *bus) {
         return r < 0 ? r : 1;
 }
 
-int bus_kernel_pop_memfd(sd_bus *bus, void **address, size_t *size) {
+int bus_kernel_pop_memfd(sd_bus *bus, void **address, size_t *mapped, size_t *allocated) {
         struct memfd_cache *c;
         int fd;
 
         assert(address);
-        assert(size);
+        assert(mapped);
+        assert(allocated);
 
         if (!bus || !bus->is_kernel)
                 return -ENOTSUP;
@@ -941,17 +942,19 @@ int bus_kernel_pop_memfd(sd_bus *bus, void **address, size_t *size) {
                         return -errno;
 
                 *address = NULL;
-                *size = 0;
+                *mapped = 0;
+                *allocated = 0;
                 return fd;
         }
 
         c = &bus->memfd_cache[--bus->n_memfd_cache];
 
         assert(c->fd >= 0);
-        assert(c->size == 0 || c->address);
+        assert(c->mapped == 0 || c->address);
 
         *address = c->address;
-        *size = c->size;
+        *mapped = c->mapped;
+        *allocated = c->allocated;
         fd = c->fd;
 
         assert_se(pthread_mutex_unlock(&bus->memfd_cache_mutex) >= 0);
@@ -966,15 +969,15 @@ static void close_and_munmap(int fd, void *address, size_t size) {
         close_nointr_nofail(fd);
 }
 
-void bus_kernel_push_memfd(sd_bus *bus, int fd, void *address, size_t size) {
+void bus_kernel_push_memfd(sd_bus *bus, int fd, void *address, size_t mapped, size_t allocated) {
         struct memfd_cache *c;
-        uint64_t max_sz = PAGE_ALIGN(MEMFD_CACHE_ITEM_SIZE_MAX);
+        uint64_t max_mapped = PAGE_ALIGN(MEMFD_CACHE_ITEM_SIZE_MAX);
 
         assert(fd >= 0);
-        assert(size == 0 || address);
+        assert(mapped == 0 || address);
 
         if (!bus || !bus->is_kernel) {
-                close_and_munmap(fd, address, size);
+                close_and_munmap(fd, address, mapped);
                 return;
         }
 
@@ -983,7 +986,7 @@ void bus_kernel_push_memfd(sd_bus *bus, int fd, void *address, size_t size) {
         if (bus->n_memfd_cache >= ELEMENTSOF(bus->memfd_cache)) {
                 assert_se(pthread_mutex_unlock(&bus->memfd_cache_mutex) >= 0);
 
-                close_and_munmap(fd, address, size);
+                close_and_munmap(fd, address, mapped);
                 return;
         }
 
@@ -992,12 +995,14 @@ void bus_kernel_push_memfd(sd_bus *bus, int fd, void *address, size_t size) {
         c->address = address;
 
         /* If overly long, let's return a bit to the OS */
-        if (size > max_sz) {
-                assert_se(ioctl(fd, KDBUS_CMD_MEMFD_SIZE_SET, &max_sz) >= 0);
-                assert_se(munmap((uint8_t*) address + max_sz, PAGE_ALIGN(size - max_sz)) >= 0);
-                c->size = max_sz;
-        } else
-                c->size = size;
+        if (mapped > max_mapped) {
+                assert_se(ioctl(fd, KDBUS_CMD_MEMFD_SIZE_SET, &max_mapped) >= 0);
+                assert_se(munmap((uint8_t*) address + max_mapped, PAGE_ALIGN(mapped - max_mapped)) >= 0);
+                c->mapped = c->allocated = max_mapped;
+        } else {
+                c->mapped = mapped;
+                c->allocated = allocated;
+        }
 
         assert_se(pthread_mutex_unlock(&bus->memfd_cache_mutex) >= 0);
 }
@@ -1008,7 +1013,7 @@ void bus_kernel_flush_memfd(sd_bus *b) {
         assert(b);
 
         for (i = 0; i < b->n_memfd_cache; i++)
-                close_and_munmap(b->memfd_cache[i].fd, b->memfd_cache[i].address, b->memfd_cache[i].size);
+                close_and_munmap(b->memfd_cache[i].fd, b->memfd_cache[i].address, b->memfd_cache[i].mapped);
 }
 
 int kdbus_translate_request_name_flags(uint64_t flags, uint64_t *kdbus_flags) {