Resize caches in all cases when cutting areas

* Adds VMCache::MovePageRange() and VMCache::Rebase() to facilitate
  this.

Applied on top of hrev45098 and rebased with the hrev45564 page_num_t to
off_t change included.

Change-Id: Ie61bf43696783e3376fb4144ddced3781aa092ba
Reviewed-on: https://review.haiku-os.org/c/haiku/+/2581
Reviewed-by: waddlesplash <waddlesplash@gmail.com>

headers/private/kernel/vm/VMCache.h

@@ -110,8 +110,11 @@ public:
 			vm_page*			LookupPage(off_t offset);
 			void				InsertPage(vm_page* page, off_t offset);
 			void				RemovePage(vm_page* page);
+			void				MovePage(vm_page* page, off_t offset);
 			void				MovePage(vm_page* page);
 			void				MoveAllPages(VMCache* fromCache);
+			void				MovePageRange(VMCache* source, off_t offset,
+									off_t size, off_t newOffset);
 
 	inline	page_num_t			WiredPagesCount() const;
 	inline	void				IncrementWiredPagesCount();
@@ -130,6 +133,7 @@ public:
 			status_t			SetMinimalCommitment(off_t commitment,
 									int priority);
 	virtual	status_t			Resize(off_t newSize, int priority);
+	virtual	status_t			Rebase(off_t newBase, int priority);
 
 			status_t			FlushAndRemoveAllPages();
 

src/system/kernel/vm/VMAnonymousCache.cpp

@@ -545,6 +545,65 @@ VMAnonymousCache::Resize(off_t newSize, int priority)
 }
 
 
+status_t
+VMAnonymousCache::Rebase(off_t newBase, int priority)
+{
+	// If the cache size shrinks, drop all swap pages beyond the new size.
+	if (fAllocatedSwapSize > 0) {
+		off_t basePage = newBase >> PAGE_SHIFT;
+		swap_block* swapBlock = NULL;
+
+		for (off_t pageIndex = 0;
+				pageIndex < basePage && fAllocatedSwapSize > 0;
+				pageIndex++) {
+			WriteLocker locker(sSwapHashLock);
+
+			// Get the swap slot index for the page.
+			swap_addr_t blockIndex = pageIndex & SWAP_BLOCK_MASK;
+			if (swapBlock == NULL || blockIndex == 0) {
+				swap_hash_key key = { this, pageIndex };
+				swapBlock = sSwapHashTable.Lookup(key);
+
+				if (swapBlock == NULL) {
+					pageIndex = ROUNDUP(pageIndex + 1, SWAP_BLOCK_PAGES);
+					continue;
+				}
+			}
+
+			swap_addr_t slotIndex = swapBlock->swap_slots[blockIndex];
+			vm_page* page;
+			if (slotIndex != SWAP_SLOT_NONE
+				&& ((page = LookupPage(pageIndex * B_PAGE_SIZE)) == NULL
+					|| !page->busy)) {
+					// TODO: We skip (i.e. leak) swap space of busy pages, since
+					// there could be I/O going on (paging in/out). Waiting is
+					// not an option as 1. unlocking the cache means that new
+					// swap pages could be added in a range we've already
+					// cleared (since the cache still has the old size) and 2.
+					// we'd risk a deadlock in case we come from the file cache
+					// and the FS holds the node's write-lock. We should mark
+					// the page invalid and let the one responsible clean up.
+					// There's just no such mechanism yet.
+				swap_slot_dealloc(slotIndex, 1);
+				fAllocatedSwapSize -= B_PAGE_SIZE;
+
+				swapBlock->swap_slots[blockIndex] = SWAP_SLOT_NONE;
+				if (--swapBlock->used == 0) {
+					// All swap pages have been freed -- we can discard the swap
+					// block.
+					sSwapHashTable.RemoveUnchecked(swapBlock);
+					object_cache_free(sSwapBlockCache, swapBlock,
+						CACHE_DONT_WAIT_FOR_MEMORY
+							| CACHE_DONT_LOCK_KERNEL_SPACE);
+				}
+			}
+		}
+	}
+
+	return VMCache::Rebase(newBase, priority);
+}
+
+
 status_t
 VMAnonymousCache::Commit(off_t size, int priority)
 {

src/system/kernel/vm/VMAnonymousCache.h

@@ -40,12 +40,15 @@ public:
 									uint32 allocationFlags);
 
 	virtual	status_t			Resize(off_t newSize, int priority);
+	virtual	status_t			Rebase(off_t newBase, int priority);
 
 	virtual	status_t			Commit(off_t size, int priority);
 	virtual	bool				HasPage(off_t offset);
 	virtual	bool				DebugHasPage(off_t offset);
 
 	virtual	int32				GuardSize()	{ return fGuardedSize; }
+	virtual	void				SetGuardSize(int32 guardSize)
+									{ fGuardedSize = guardSize; }
 
 	virtual	status_t			Read(off_t offset, const generic_io_vec* vecs,
 									size_t count, uint32 flags,

src/system/kernel/vm/VMAnonymousNoSwapCache.h

@@ -26,6 +26,8 @@ public:
 	virtual	bool				HasPage(off_t offset);
 
 	virtual	int32				GuardSize()	{ return fGuardedSize; }
+	virtual	void				SetGuardSize(int32 guardSize)
+									{ fGuardedSize = guardSize; }
 
 	virtual	status_t			Read(off_t offset, const generic_io_vec *vecs,
 									 size_t count,uint32 flags,

src/system/kernel/vm/VMCache.cpp

@@ -187,6 +187,29 @@ class Resize : public VMCacheTraceEntry {
 };
 
 
+class Rebase : public VMCacheTraceEntry {
+	public:
+		Rebase(VMCache* cache, off_t base)
+			:
+			VMCacheTraceEntry(cache),
+			fOldBase(cache->virtual_base),
+			fBase(base)
+		{
+			Initialized();
+		}
+
+		virtual void AddDump(TraceOutput& out)
+		{
+			out.Print("vm cache rebase: cache: %p, base: %lld -> %lld", fCache,
+				fOldBase, fBase);
+		}
+
+	private:
+		off_t	fOldBase;
+		off_t	fBase;
+};
+
+
 class AddConsumer : public VMCacheTraceEntry {
 	public:
 		AddConsumer(VMCache* cache, VMCache* consumer)
@@ -825,11 +848,12 @@ VMCache::RemovePage(vm_page* page)
 }
 
 
-/*!	Moves the given page from its current cache inserts it into this cache.
+/*!	Moves the given page from its current cache inserts it into this cache
+	at the given offset.
 	Both caches must be locked.
 */
 void
-VMCache::MovePage(vm_page* page)
+VMCache::MovePage(vm_page* page, off_t offset)
 {
 	VMCache* oldCache = page->Cache();
 
@@ -841,6 +865,9 @@ VMCache::MovePage(vm_page* page)
 	oldCache->page_count--;
 	T2(RemovePage(oldCache, page));
 
+	// change the offset
+	page->cache_offset = offset >> PAGE_SHIFT;
+
 	// insert here
 	pages.Insert(page);
 	page_count++;
@@ -854,6 +881,15 @@ VMCache::MovePage(vm_page* page)
 	T2(InsertPage(this, page, page->cache_offset << PAGE_SHIFT));
 }
 
+/*!	Moves the given page from its current cache inserts it into this cache.
+	Both caches must be locked.
+*/
+void
+VMCache::MovePage(vm_page* page)
+{
+	MovePage(page, page->cache_offset << PAGE_SHIFT);
+}
+
 
 /*!	Moves all pages from the given cache to this one.
 	Both caches must be locked. This cache must be empty.
@@ -888,6 +924,27 @@ VMCache::MoveAllPages(VMCache* fromCache)
 }
 
 
+/*!	Moves the given pages from their current cache and inserts them into this
+	cache. Both caches must be locked.
+*/
+void
+VMCache::MovePageRange(VMCache* source, off_t offset, off_t size,
+		off_t newOffset)
+{
+	page_num_t startPage = offset >> PAGE_SHIFT;
+	page_num_t endPage = (offset + size + B_PAGE_SIZE - 1) >> PAGE_SHIFT;
+	int32 offsetChange = (int32)(newOffset - offset);
+
+	VMCachePagesTree::Iterator it = source->pages.GetIterator(startPage, true,
+		true);
+	for (vm_page* page = it.Next();
+				page != NULL && page->cache_offset < endPage;
+				page = it.Next()) {
+		MovePage(page, (page->cache_offset << PAGE_SHIFT) + offsetChange);
+	}
+}
+
+
 /*!	Waits until one or more events happened for a given page which belongs to
 	this cache.
 	The cache must be locked. It will be unlocked by the method. \a relock
@@ -1141,6 +1198,71 @@ VMCache::Resize(off_t newSize, int priority)
 	return B_OK;
 }
 
+/*!	This function updates the virtual_base field of the cache.
+	If needed, it will free up all pages that don't belong to the cache anymore.
+	The cache lock must be held when you call it.
+	Since removed pages don't belong to the cache any longer, they are not
+	written back before they will be removed.
+
+	Note, this function may temporarily release the cache lock in case it
+	has to wait for busy pages.
+*/
+status_t
+VMCache::Rebase(off_t newBase, int priority)
+{
+	TRACE(("VMCache::Rebase(cache %p, newBase %Ld) old base %Ld\n",
+		this, newBase, this->virtual_base));
+	this->AssertLocked();
+
+	T(Rebase(this, newBase));
+
+	status_t status = Commit(virtual_end - newBase, priority);
+	if (status != B_OK)
+		return status;
+
+	uint32 basePage = (uint32)(newBase >> PAGE_SHIFT);
+
+	if (newBase > virtual_base) {
+		// we need to remove all pages in the cache outside of the new virtual
+		// size
+		VMCachePagesTree::Iterator it = pages.GetIterator();
+		for (vm_page* page = it.Next();
+				page != NULL && page->cache_offset < basePage;
+				page = it.Next()) {
+			if (page->busy) {
+				if (page->busy_writing) {
+					// We cannot wait for the page to become available
+					// as we might cause a deadlock this way
+					page->busy_writing = false;
+						// this will notify the writer to free the page
+				} else {
+					// wait for page to become unbusy
+					WaitForPageEvents(page, PAGE_EVENT_NOT_BUSY, true);
+
+					// restart from the start of the list
+					it = pages.GetIterator();
+				}
+				continue;
+			}
+
+			// remove the page and put it into the free queue
+			DEBUG_PAGE_ACCESS_START(page);
+			vm_remove_all_page_mappings(page);
+			ASSERT(page->WiredCount() == 0);
+				// TODO: Find a real solution! If the page is wired
+				// temporarily (e.g. by lock_memory()), we actually must not
+				// unmap it!
+			RemovePage(page);
+			vm_page_free(this, page);
+				// Note: When iterating through a IteratableSplayTree
+				// removing the current node is safe.
+		}
+	}
+
+	virtual_base = newBase;
+	return B_OK;
+}
+
 
 /*!	You have to call this function with the VMCache lock held. */
 status_t

src/system/kernel/vm/vm.cpp

@@ -676,9 +676,10 @@ cut_area(VMAddressSpace* addressSpace, VMArea* area, addr_t address,
 		addr_t oldBase = area->Base();
 		addr_t newBase = lastAddress + 1;
 		size_t newSize = areaLast - lastAddress;
+		size_t newOffset = newBase - oldBase;
 
 		// unmap pages
-		unmap_pages(area, oldBase, newBase - oldBase);
+		unmap_pages(area, oldBase, newOffset);
 
 		// resize the area
 		status_t error = addressSpace->ShrinkAreaHead(area, newSize,
@@ -686,9 +687,17 @@ cut_area(VMAddressSpace* addressSpace, VMArea* area, addr_t address,
 		if (error != B_OK)
 			return error;
 
-		// TODO: If no one else uses the area's cache, we should resize it, too!
-
-		area->cache_offset += newBase - oldBase;
+		// If no one else uses the area's cache, we can resize it, too.
+		if (cache->areas == area && area->cache_next == NULL
+			&& cache->consumers.IsEmpty()
+			&& cache->type == CACHE_TYPE_RAM) {
+			// Since VMCache::Rebase() can temporarily drop the lock, we must
+			// unlock all lower caches to prevent locking order inversion.
+			cacheChainLocker.Unlock(cache);
+			cache->Rebase(cache->virtual_base + newOffset, priority);
+			cache->ReleaseRefAndUnlock();
+		}
+		area->cache_offset += newOffset;
 
 		return B_OK;
 	}
@@ -696,7 +705,6 @@ cut_area(VMAddressSpace* addressSpace, VMArea* area, addr_t address,
 	// The tough part -- cut a piece out of the middle of the area.
 	// We do that by shrinking the area to the begin section and creating a
 	// new area for the end section.
-
 	addr_t firstNewSize = address - area->Base();
 	addr_t secondBase = lastAddress + 1;
 	addr_t secondSize = areaLast - lastAddress;
@@ -711,26 +719,74 @@ cut_area(VMAddressSpace* addressSpace, VMArea* area, addr_t address,
 	if (error != B_OK)
 		return error;
 
-	// TODO: If no one else uses the area's cache, we might want to create a
-	// new cache for the second area, transfer the concerned pages from the
-	// first cache to it and resize the first cache.
-
-	// map the second area
 	virtual_address_restrictions addressRestrictions = {};
 	addressRestrictions.address = (void*)secondBase;
 	addressRestrictions.address_specification = B_EXACT_ADDRESS;
 	VMArea* secondArea;
-	error = map_backing_store(addressSpace, cache,
-		area->cache_offset + (secondBase - area->Base()), area->name,
-		secondSize, area->wiring, area->protection, REGION_NO_PRIVATE_MAP, 0,
-		&addressRestrictions, kernel, &secondArea, NULL);
-	if (error != B_OK) {
-		addressSpace->ShrinkAreaTail(area, oldSize, allocationFlags);
-		return error;
-	}
 
-	// We need a cache reference for the new area.
-	cache->AcquireRefLocked();
+	// If no one else uses the area's cache and it's an anonymous cache, we
+	// can split it.
+	if (cache->areas == area && area->cache_next == NULL
+		&& cache->consumers.IsEmpty()
+		&& cache->type == CACHE_TYPE_RAM) {
+		// Create a new cache for the second area.
+		VMCache* secondCache;
+		error = VMCacheFactory::CreateAnonymousCache(secondCache, false, 0, 0,
+			dynamic_cast<VMAnonymousNoSwapCache*>(cache) == NULL,
+			VM_PRIORITY_USER);
+		if (error != B_OK) {
+			addressSpace->ShrinkAreaTail(area, oldSize, allocationFlags);
+			return error;
+		}
+
+		secondCache->Lock();
+
+		// Transfer the concerned pages from the first cache.
+		secondCache->MovePageRange(cache, secondBase - area->Base()
+			+ area->cache_offset, secondSize, area->cache_offset);
+		secondCache->virtual_base = area->cache_offset;
+		secondCache->virtual_end = area->cache_offset + secondSize;
+
+		// Since VMCache::Resize() can temporarily drop the lock, we must
+		// unlock all lower caches to prevent locking order inversion.
+		cacheChainLocker.Unlock(cache);
+		cache->Resize(cache->virtual_base + firstNewSize, priority);
+		// Don't unlock the cache yet because we might have to resize it
+		// back.
+
+		// Map the second area.
+		error = map_backing_store(addressSpace, secondCache, area->cache_offset,
+			area->name, secondSize, area->wiring, area->protection,
+			REGION_NO_PRIVATE_MAP, 0, &addressRestrictions, kernel, &secondArea,
+			NULL);
+		if (error != B_OK) {
+			// Restore the original cache.
+			cache->Resize(cache->virtual_base + oldSize, priority);
+			// Move the pages back.
+			cache->MovePageRange(secondCache, area->cache_offset, secondSize,
+				secondBase - area->Base() + area->cache_offset);
+			cache->ReleaseRefAndUnlock();
+			secondCache->ReleaseRefAndUnlock();
+			addressSpace->ShrinkAreaTail(area, oldSize, allocationFlags);
+			return error;
+		}
+
+		// Now we can unlock it.
+		cache->ReleaseRefAndUnlock();
+		secondCache->Unlock();
+	} else {
+		error = map_backing_store(addressSpace, cache, area->cache_offset
+			+ (secondBase - area->Base()),
+			area->name, secondSize, area->wiring, area->protection,
+			REGION_NO_PRIVATE_MAP, 0, &addressRestrictions, kernel, &secondArea,
+			NULL);
+		if (error != B_OK) {
+			addressSpace->ShrinkAreaTail(area, oldSize, allocationFlags);
+			return error;
+		}
+		// We need a cache reference for the new area.
+		cache->AcquireRefLocked();
+	}
 
 	if (_secondArea != NULL)
 		*_secondArea = secondArea;