I've wanted to write a post about working with virtual memory for quite some time now . And when @jimsagevid in reply to my tweet wrote about it, I realized that the time had come.
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objecto *objects[MAXOBJECTS]
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#define MAXOBJECTS 1000000000ULL
objecto **objects = virtualalloc(MAXOBJECTS * sizeof(objecto ));
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— virtualalloc()
, . Windows VirtualAlloc(), Linux mmap().
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uint32_t num_tanks;
tank_t tanks[MAX_TANKS];
uint32_t num_bullets;
bullet_t bullets[MAX_BULLETS];
...
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MAX¨C13C 1 :
#define GB 1000000000
uint32_t num_tanks;
tank_t *tanks = virtual_alloc(GB);
uint32_t num_bullets;
bullet_t *bullets = virtual_alloc(GB);
ID
(ID) . :
uint64_t allocate_id(system_t *sys)
{
return sys->next_free_id++;
}
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:
system_id_t *allocate_id(system_t *sys)
{
if (!sys->id_block || sys->id_block_used == PAGE_SIZE) {
sys->id_block = virtual_alloc(PAGE_SIZE);
sys->id_block_used = 0;
}
return (system_id_t *)(sys->id_block + sys->id_block_used++);
}
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void *eop_malloc(uint64_t size)
{
uint64_t pages = (size + PAGE_SIZE - 1) / PAGE_SIZE;
char *base = virtual_alloc(pages * PAGE_SIZE);
uint64_t offset = pages * PAGE_SIZE - size;
return base + offset;
}
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enum {BUFFER_SIZE = 8*1024};
struct ring_buffer_t {
uint8_t data[BUFFER_SIZE];
uint64_t read;
uint64_t written;
};
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void write(ring_buffer_t *rb, uint8_t *p, uint64_t n)
{
uint64_t offset = rb->written % BUFFER_SIZE;
uint64_t space = BUFFER_SIZE - offset;
uint64_t first_write = n < space ? n : space;
memcpy(rb->data + offset, p, first_write);
memcpy(rb->data, p + first_write, n - first_write);
rb->written += n;
}
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void write(ring_buffer_t *rb, uint8_t *p, uint64_t n)
{
memcpy(rb->data + (rb->written % BUFFER_SIZE), p, n);
rb->written += n;
}
uint8_t *read(ring_buffer_t *rb, uint64_t n)
{
uint8_t *p = rb->data + (rb->read % BUFFER_SIZE);
rb->read += n;
return p;
}
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Linux
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) (vm.overcommit_memory = 2
). . https://www.kernel.org/doc/Documentation/vm/overcommit-accounting
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.
mmap()
, Linux mmap()
PROT_NONE
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.
— MAP_NORESERVE
PROT_NONE
, overcommit_memory = 2
, MAP_NORESERVE
. . https://lwn.net/Articles/627557/
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