added option to lock disk cache in physical memory

docs/manual.rst

@@ -3253,6 +3253,8 @@ that will be sent to the tracker. The user-agent is a good way to identify your
 		int seeding_piece_quota;
 
 		int max_sparse_regions;
+
+		bool lock_disk_cache;
 	};
 
 ``user_agent`` this is the client identification to the tracker.
@@ -3584,6 +3586,10 @@ that will maintain or decrease the number of sparse regions are
 prioritized. To disable this functionality, set this to 0. It defaults
 to 0 on all platforms except windows.
 
+``lock_disk_cache`` if lock disk cache is set to true the disk cache
+that's in use, will be locked in physical memory, preventing it from
+being swapped out.
+
 pe_settings
 ===========
 

include/libtorrent/disk_io_thread.hpp

@@ -181,10 +181,14 @@ namespace libtorrent
 
 		void release_memory();
 
+	protected:
+
 		// number of bytes per block. The BitTorrent
 		// protocol defines the block size to 16 KiB.
 		const int m_block_size;
 
+		session_settings m_settings;
+
 	private:
 
 		// this only protects the pool allocator
@@ -307,8 +311,6 @@ namespace libtorrent
 		cache_status m_cache_stats;
 		int m_num_cached_blocks;
 
-		session_settings m_settings;
-
 #ifdef TORRENT_DISK_STATS
 		std::ofstream m_log;
 #endif

include/libtorrent/session_settings.hpp

@@ -155,6 +155,9 @@ namespace libtorrent
 			, max_sparse_regions(30000)
 #else
 			, max_sparse_regions(0)
+#endif
+#ifndef TORRENT_DISABLE_MLOCK
+			, lock_disk_cache(true)
 #endif
 		{}
 
@@ -513,6 +516,13 @@ namespace libtorrent
 		// don't use unless you have to, it screws with rarest-first
 		// piece selection, and reduces swarm performance
 		int max_sparse_regions;
+
+#ifndef TORRENT_DISABLE_MLOCK
+		// if this is set to true, the memory allocated for the
+		// disk cache will be locked in physical RAM, never to
+		// be swapped out
+		bool lock_disk_cache;
+#endif
 	};
 
 #ifndef TORRENT_DISABLE_DHT

src/disk_io_thread.cpp

@@ -43,6 +43,10 @@ POSSIBILITY OF SUCH DAMAGE.
 #include "libtorrent/time.hpp"
 #endif
 
+#ifndef TORRENT_DISABLE_MLOCK
+#include <sys/mman.h>
+#endif
+
 namespace libtorrent
 {
 	disk_buffer_pool::disk_buffer_pool(int block_size)
@@ -79,6 +83,17 @@ namespace libtorrent
 #else
 		char* ret = (char*)m_pool.ordered_malloc();
 #endif
+#ifndef TORRENT_DISABLE_MLOCK
+		if (m_settings.lock_disk_cache)
+		{
+#ifdef TORRENT_WINDOWS
+			VirtualLock(ret, m_block_size);
+#else
+			mlock(ret, m_block_size);
+#endif		
+		}
+#endif
+
 #ifdef TORRENT_STATS
 		++m_allocations;
 		++m_categories[category];
@@ -101,6 +116,16 @@ namespace libtorrent
 		m_log << log_time() << " " << category << ": " << m_categories[category] << "\n";
 		m_buf_to_category.erase(buf);
 #endif
+#ifndef TORRENT_DISABLE_MLOCK
+		if (m_settings.lock_disk_cache)
+		{
+#ifdef TORRENT_WINDOWS
+			VirtualUnlock(buf, m_block_size);
+#else
+			munlock(buf, m_block_size);
+#endif		
+		}
+#endif
 #ifdef TORRENT_DISABLE_POOL_ALLOCATOR
 		page_aligned_allocator::free(buf);
 #else
@@ -116,6 +141,16 @@ namespace libtorrent
 #else
 		char* ret = (char*)m_pool.ordered_malloc(num_blocks);
 #endif
+#ifndef TORRENT_DISABLE_MLOCK
+		if (m_settings.lock_disk_cache)
+		{
+#ifdef TORRENT_WINDOWS
+			VirtualLock(ret, m_block_size * num_blocks);
+#else
+			mlock(ret, m_block_size * num_blocks);
+#endif		
+		}
+#endif
 #ifdef TORRENT_STATS
 		m_allocations += num_blocks;
 		m_categories[category] += num_blocks;
@@ -139,6 +174,16 @@ namespace libtorrent
 		m_log << log_time() << " " << category << ": " << m_categories[category] << "\n";
 		m_buf_to_category.erase(buf);
 #endif
+#ifndef TORRENT_DISABLE_MLOCK
+		if (m_settings.lock_disk_cache)
+		{
+#ifdef TORRENT_WINDOWS
+			VirtualUnlock(buf, m_block_size * num_blocks);
+#else
+			munlock(buf, m_block_size * num_blocks);
+#endif		
+		}
+#endif
 #ifdef TORRENT_DISABLE_POOL_ALLOCATOR
 		page_aligned_allocator::free(buf);
 #else

src/session_impl.cpp

@@ -589,6 +589,9 @@ namespace aux {
 		bool update_disk_io_thread = false;
 		if (m_settings.cache_size != s.cache_size
 			|| m_settings.cache_expiry != s.cache_expiry
+#ifndef TORRENT_DISABLE_MLOCK
+			|| m_settings.lock_disk_cache != s.lock_disk_cache
+#endif
 			|| m_settings.use_read_cache != s.use_read_cache)
 			update_disk_io_thread = true;