kernel/vm: Track fault and copy counts in VMCache.

This solves a TODO for reporting CoW counts in area_info, and paves
the way for adaptive handling of pre-faulting based on how many
faults a cache has handled.

Change-Id: I4ecd7cf46b794c51acac87184fef49ea5ce76743
Reviewed-on: https://review.haiku-os.org/c/haiku/+/8873
Haiku-Format: Haiku-format Bot <[email protected]>
Reviewed-by: waddlesplash <[email protected]>

headers/private/kernel/vm/VMCache.h

@@ -174,6 +174,16 @@ public:
 	virtual	status_t			Fault(struct VMAddressSpace *aspace,
 									off_t offset);
 
+	inline	uint64				FaultCount() const
+									{ return fFaultCount; }
+	inline	void				IncrementFaultCount()
+									{ fFaultCount++; }
+
+	inline	uint64				CopiedPagesCount() const
+									{ return fCopiedPagesCount; }
+	inline	void				IncrementCopiedPagesCount()
+									{ fCopiedPagesCount++; }
+
 	virtual	void				Merge(VMCache* source);
 
 	virtual	status_t			AcquireUnreferencedStoreRef();
@@ -228,7 +238,10 @@ private:
 			PageEventWaiter*	fPageEventWaiters;
 			void*				fUserData;
 			VMCacheRef*			fCacheRef;
+
 			page_num_t			fWiredPagesCount;
+			uint64				fFaultCount;
+			uint64				fCopiedPagesCount;
 };
 
 

src/system/kernel/vm/VMCache.cpp

@@ -642,6 +642,8 @@ VMCache::Init(uint32 cacheType, uint32 allocationFlags)
 	temporary = 0;
 	page_count = 0;
 	fWiredPagesCount = 0;
+	fFaultCount = 0;
+	fCopiedPagesCount = 0;
 	type = cacheType;
 	fPageEventWaiters = NULL;
 

src/system/kernel/vm/vm.cpp

@@ -4405,6 +4405,7 @@ fault_get_page(PageFaultContext& context)
 
 		context.cacheChainLocker.RelockCaches(true);
 		sourcePage->Cache()->MarkPageUnbusy(sourcePage);
+		sourcePage->Cache()->IncrementCopiedPagesCount();
 
 		// insert the new page into our cache
 		context.topCache->InsertPage(page, context.cacheOffset);
@@ -4666,8 +4667,9 @@ vm_soft_fault(VMAddressSpace* addressSpace, addr_t originalAddress,
 			*wirePage = context.page;
 		}
 
-		DEBUG_PAGE_ACCESS_END(context.page);
+		context.page->Cache()->IncrementFaultCount();
 
+		DEBUG_PAGE_ACCESS_END(context.page);
 		break;
 	}
 
@@ -4920,16 +4922,18 @@ fill_area_info(struct VMArea* area, area_info* info, size_t size)
 	info->protection = area->protection;
 	info->lock = area->wiring;
 	info->team = area->address_space->ID();
-	info->copy_count = 0;
-	info->in_count = 0;
-	info->out_count = 0;
-		// TODO: retrieve real values here!
 
 	VMCache* cache = vm_area_get_locked_cache(area);
 
 	// Note, this is a simplification; the cache could be larger than this area
 	info->ram_size = cache->page_count * B_PAGE_SIZE;
 
+	info->copy_count = cache->CopiedPagesCount();
+
+	info->in_count = 0;
+	info->out_count = 0;
+		// TODO: retrieve real values here!
+
 	vm_area_put_locked_cache(cache);
 }