[Minor] Arm64: Implement poor man slabs

Issue: #2906

diff --git a/contrib/lua-lpeg/lpvm.c b/contrib/lua-lpeg/lpvm.c
index 711fe026dc44122f53ed75fa471395c795e25ce4..4417128268987805fd62582000118da25f71b02f 100644 (file)
--- a/contrib/lua-lpeg/lpvm.c
+++ b/contrib/lua-lpeg/lpvm.c
@@ -19,6 +19,20 @@
 
 #include <sys/mman.h>
 
+#define MAX_PIECES (1u << 2u)
+
+/* 64 bytes, 1 cache line */
+struct poor_slab {
+       struct slab_piece {
+               unsigned char *ptr;
+               uint32_t sz;
+               uint32_t occupied;
+       } pieces[MAX_PIECES];
+};
+
+/* Used to optimize pages allocation */
+struct poor_slab slabs;
+
 static uint64_t xorshifto_seed[2] = {0xdeadbabe, 0xdeadbeef};
 
 static inline uint64_t
@@ -33,6 +47,15 @@ lpeg_allocate_mem_low (size_t sz)
        unsigned flags = MAP_PRIVATE | MAP_ANON;
        void *base_addr = NULL;
 
+       /* Check slabs */
+       for (unsigned i = 0; i < MAX_PIECES; i ++) {
+               if (!slabs.pieces[i].occupied && slabs.pieces[i].sz == sz) {
+                       /* Reuse, short path */
+                       slabs.pieces[i].occupied = 1;
+                       return slabs.pieces[i].ptr + sizeof (size_t);
+               }
+       }
+
 #ifdef MAP_32BIT
        flags |= MAP_32BIT;
 #else
@@ -52,6 +75,25 @@ lpeg_allocate_mem_low (size_t sz)
        assert (cp != NULL);
        memcpy (cp, &sz, sizeof (sz));
 
+       for (unsigned i = 0; i < MAX_PIECES; i ++) {
+               if (slabs.pieces[i].sz == 0) {
+                       /* Store piece */
+                       slabs.pieces[i].sz = sz;
+                       slabs.pieces[i].ptr = cp;
+                       slabs.pieces[i].occupied = 1;
+
+                       return cp + sizeof (sz);
+               }
+       }
+
+       /* Not enough free pieces, pop some */
+       unsigned sel = ((uintptr_t)cp) & ((MAX_PIECES * 2) - 1);
+       /* Here we free memory in fact */
+       munmap (slabs.pieces[sel].ptr, slabs.pieces[sel].sz);
+       slabs.pieces[sel].sz = sz;
+       slabs.pieces[sel].ptr = cp;
+       slabs.pieces[sel].occupied = 1;
+
        return cp + sizeof (sz);
 }
 
@@ -61,8 +103,20 @@ lpeg_free_mem_low(void *p)
        unsigned char *cp = (unsigned char *)p;
        size_t sz;
 
-       memcpy (&sz, cp - sizeof (sz), sizeof (sz));
-       munmap (cp - sizeof (sz), sz + sizeof (sz));
+       /* Base address */
+       cp -= sizeof (sz);
+       memcpy (&sz, cp, sizeof (sz));
+
+       for (unsigned i = 0; i < MAX_PIECES; i ++) {
+               if (slabs.pieces[i].occupied && slabs.pieces[i].ptr == cp) {
+                       /* Return back */
+                       slabs.pieces[i].occupied = 0;
+
+                       return;
+               }
+       }
+
+       /* No match, unmapped by allocation */
 }
 
 /* initial size for call/backtrack stack */