From ae8488fb91905fec0291d3edbec6ec1bbdb1a6c9 Mon Sep 17 00:00:00 2001
From: Arvid Norberg <arvid@libtorrent.org>
Date: Sat, 23 May 2009 19:27:27 +0000
Subject: [PATCH] improved read cache memory efficiency

---
 ChangeLog                               | 1 +
 docs/manual.rst                         | 6 ++++++
 include/libtorrent/session_settings.hpp | 5 +++++
 src/disk_io_thread.cpp                  | 3 +++
 src/session_impl.cpp                    | 1 +
 5 files changed, 16 insertions(+)

diff --git a/ChangeLog b/ChangeLog
index 79bb48a0b..536988313 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,4 @@
+	* improved read cache memory efficiency
 	* added another cache flush algorithm to write the largest
 	  contiguous blocks instead of the least recently used
 	* introduced a mechanism to be lighter on the disk when checking torrents
diff --git a/docs/manual.rst b/docs/manual.rst
index 84561b90d..af5e26ecb 100644
--- a/docs/manual.rst
+++ b/docs/manual.rst
@@ -3448,6 +3448,8 @@ session_settings
 		{ lru, largest_contiguous };
 
 		disk_cache_algo_t disk_cache_algorithm;
+
+		int read_cache_line_size;
 	};
 
 ``user_agent`` this is the client identification to the tracker.
@@ -3839,6 +3841,10 @@ value. ``session_settings::largest_contiguous`` will flush the largest
 sequences of contiguous blocks from the write cache, regarless of the
 piece's last use time.
 
+``read_cache_line_size`` is the number of blocks to read into the read
+cache when a read cache miss occurs. Setting this to 0 is essentially
+the same thing as disabling read cache. The number of blocks read
+into the read cache is always capped by the piece boundry.
 
 pe_settings
 ===========
diff --git a/include/libtorrent/session_settings.hpp b/include/libtorrent/session_settings.hpp
index 15c797be3..8e43e2fa8 100644
--- a/include/libtorrent/session_settings.hpp
+++ b/include/libtorrent/session_settings.hpp
@@ -168,6 +168,7 @@ namespace libtorrent
 			, optimize_hashing_for_speed(true)
 			, file_checks_delay_per_block(0)
 			, disk_cache_algorithm(lru)
+			, read_cache_line_size(16)
 		{}
 
 		// this is the user agent that will be sent to the tracker
@@ -576,6 +577,10 @@ namespace libtorrent
 		{ lru, largest_contiguous };
 
 		disk_cache_algo_t disk_cache_algorithm;
+
+		// the number of blocks that will be read ahead
+		// when reading a block into the read cache
+		int read_cache_line_size;
 	};
 
 #ifndef TORRENT_DISABLE_DHT
diff --git a/src/disk_io_thread.cpp b/src/disk_io_thread.cpp
index 6faf84386..89e0b06c6 100644
--- a/src/disk_io_thread.cpp
+++ b/src/disk_io_thread.cpp
@@ -720,6 +720,7 @@ namespace libtorrent
 		int blocks_in_piece = (piece_size + m_block_size - 1) / m_block_size;
 
 		int end_block = start_block;
+		int num_read = 0;
 		for (int i = start_block; i < blocks_in_piece
 			&& (in_use() < m_settings.cache_size
 				|| (options & ignore_cache_size)); ++i)
@@ -736,6 +737,8 @@ namespace libtorrent
 			++m_cache_stats.cache_size;
 			++m_cache_stats.read_cache_size;
 			++end_block;
+			++num_read;
+			if (num_read >= m_settings.read_cache_line_size) break;
 		}
 
 		if (end_block == start_block) return -2;
diff --git a/src/session_impl.cpp b/src/session_impl.cpp
index bb5ba0271..8a37702b0 100644
--- a/src/session_impl.cpp
+++ b/src/session_impl.cpp
@@ -641,6 +641,7 @@ namespace aux {
 			|| m_settings.optimize_hashing_for_speed != s.optimize_hashing_for_speed
 			|| m_settings.file_checks_delay_per_block != s.file_checks_delay_per_block
 			|| m_settings.disk_cache_algorithm != s.disk_cache_algorithm
+			|| m_settings.read_cache_line_size != s.read_cache_line_size
 #ifndef TORRENT_DISABLE_MLOCK
 			|| m_settings.lock_disk_cache != s.lock_disk_cache
 #endif