Merge tag 'pull-request-2023-06-29' of https://gitlab.com/thuth/qemu into staging

[mirror_qemu.git] / docs / qcow2-cache.txt

diff --git a/docs/qcow2-cache.txt b/docs/qcow2-cache.txt
index d57f40986139ba167e2372cb90c3381606daf0c7..5f763aa6bbfe3700ba1324d04064589c7a2a447b 100644 (file)
--- a/docs/qcow2-cache.txt
+++ b/docs/qcow2-cache.txt
@@ -1,6 +1,6 @@
 qcow2 L2/refcount cache configuration
 =====================================
-Copyright (C) 2015, 2018 Igalia, S.L.
+Copyright (C) 2015, 2018-2020 Igalia, S.L.
 Author: Alberto Garcia <berto@igalia.com>
 
 This work is licensed under the terms of the GNU GPL, version 2 or
@@ -222,3 +222,20 @@ support this functionality, and is 0 (disabled) on other platforms.
 This functionality currently relies on the MADV_DONTNEED argument for
 madvise() to actually free the memory. This is a Linux-specific feature,
 so cache-clean-interval is not supported on other systems.
+
+
+Extended L2 Entries
+-------------------
+All numbers shown in this document are valid for qcow2 images with normal
+64-bit L2 entries.
+
+Images with extended L2 entries need twice as much L2 metadata, so the L2
+cache size must be twice as large for the same disk space.
+
+   disk_size = l2_cache_size * cluster_size / 16
+
+i.e.
+
+   l2_cache_size = disk_size * 16 / cluster_size
+
+Refcount blocks are not affected by this.