This test program allocates 10M per second and when
memory pressure notify happens, it releases 20M.
I tested this patch on 512M qemu machine with 3 test program.
I saw some swapout but not too many and even didn't see OOM.
It obviously reduces swap out.
Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
---
poll.c | 121 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 files changed, 121 insertions(+), 0 deletions(-)
create mode 100644 poll.c
diff --git a/poll.c b/poll.c
new file mode 100644
index 0000000..3215f8b
--- /dev/null
+++ b/poll.c
@@ -0,0 +1,121 @@
+#include <poll.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <pthread.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
+
+#define ALLOC_UNIT 10 /* MB */
+#define FREE_UNIT 20 /* MB */
+
+void alloc_memory();
+void free_memory();
+
+unsigned int total_memory = 0; /* MB */
+
+pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
+
+/*
+ * If total memory is higher than 200M
+ */
+bool memory_full()
+{
+ return total_memory >= 400 ? true : false;
+}
+
+struct alloc_chunk {
+ void *ptr;
+ struct alloc_chunk *next;
+};
+
+struct alloc_chunk head_chunk;
+
+void init_alloc_chunk(void)
+{
+ head_chunk.ptr = NULL;
+ head_chunk.next = NULL;
+}
+
+void add_memory(void *ptr)
+{
+ struct alloc_chunk *new_chunk = malloc(sizeof(struct alloc_chunk));
+ new_chunk->ptr = ptr;
+
+ pthread_mutex_lock(&mutex);
+ new_chunk->next = head_chunk.next;
+ head_chunk.next = new_chunk;
+ total_memory += ALLOC_UNIT;
+ pthread_mutex_unlock(&mutex);
+
+ printf("[%d] Add total memory %d(MB)\n", getpid(), total_memory);
+}
+
+void alloc_memory(void)
+{
+ while(1) {
+ if (memory_full()) {
+ sleep(10);
+ continue;
+ }
+
+ void *new = malloc(ALLOC_UNIT*1024*1024);
+ memset(new, 0, ALLOC_UNIT*1024*1024);
+ add_memory(new);
+ sleep(1);
+ }
+}
+
+void free_memory(void)
+{
+ int count = FREE_UNIT / ALLOC_UNIT;
+ while(count--) {
+ struct alloc_chunk *chunk = head_chunk.next;
+ if (chunk == NULL)
+ break;
+
+ pthread_mutex_lock(&mutex);
+ head_chunk.next = chunk->next;
+ total_memory -= ALLOC_UNIT;
+ pthread_mutex_unlock(&mutex);
+
+ free(chunk->ptr);
+ free(chunk);
+
+ printf("[%d] Free total memory %d(MB)\n", getpid(), total_memory);
+ }
+}
+
+void *poll_thread(void *dummy)
+{
+ struct pollfd pfd;
+ int fd = open("/dev/low_mem_notify", O_RDONLY);
+ if (fd == -1) {
+ fprintf(stderr, "Fail to open\n");
+ return;
+ }
+
+ pfd.fd = fd;
+ pfd.events = POLLIN;
+
+ while(1) {
+ poll(&pfd, 1, -1);
+ free_memory();
+ }
+}
+
+int main()
+{
+ pthread_t threadid;
+ init_alloc_chunk();
+
+ if (pthread_create(&threadid, NULL, poll_thread, NULL)) {
+ fprintf(stderr, "pthread create fail\n");
+ return 1;
+ }
+
+ alloc_memory();
+ return 0;
+}
--
1.7.7.5
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