Kernel+SystemMonitor: Add fault counters

This patch adds three separate per-process fault counters:

- Inode faults

    An inode fault happens when we've memory-mapped a file from disk
    and we end up having to load 1 page (4KB) of the file into memory.

- Zero faults

    Memory returned by mmap() is lazily zeroed out. Every time we have
    to zero out 1 page, we count a zero fault.

- CoW faults

    VM objects can be shared by multiple mappings that make their own
    unique copy iff they want to modify it. The typical reason here is
    memory shared between a parent and child process.

Kernel/VM/MemoryManager.cpp

@@ -296,6 +296,7 @@ bool MemoryManager::zero_page(Region& region, unsigned page_index_in_region)
     sti();
     LOCKER(vmo.m_paging_lock);
     cli();
+
     if (!vmo_page.is_null()) {
 #ifdef PAGE_FAULT_DEBUG
         dbgprintf("MM: zero_page() but page already present. Fine with me!\n");
@@ -303,6 +304,10 @@ bool MemoryManager::zero_page(Region& region, unsigned page_index_in_region)
         remap_region_page(region, page_index_in_region);
         return true;
     }
+
+    if (current)
+        current->process().did_zero_fault();
+
     auto physical_page = allocate_user_physical_page(ShouldZeroFill::Yes);
 #ifdef PAGE_FAULT_DEBUG
     dbgprintf("      >> ZERO P%p\n", physical_page->paddr().get());
@@ -325,6 +330,9 @@ bool MemoryManager::copy_on_write(Region& region, unsigned page_index_in_region)
         return true;
     }
 
+    if (current)
+        current->process().did_cow_fault();
+
 #ifdef PAGE_FAULT_DEBUG
     dbgprintf("    >> It's a COW page and it's time to COW!\n");
 #endif
@@ -367,6 +375,9 @@ bool MemoryManager::page_in_from_inode(Region& region, unsigned page_index_in_re
         return true;
     }
 
+    if (current)
+        current->process().did_inode_fault();
+
 #ifdef MM_DEBUG
     dbgprintf("MM: page_in_from_inode ready to read from inode\n");
 #endif