fs: Add subsection on ext4 fast commits.

diff --git a/Filesystems.m4 b/Filesystems.m4
index 40dedd1aca314193f2748c886aad706533223604..7750dab91c6fdbd2ef701e0d355fbd51b731ebfd 100644 (file)
--- a/Filesystems.m4
+++ b/Filesystems.m4
@@ -829,6 +829,27 @@ it's best to make the LV slightly larger than necessary and then
 enlarge the filesystem to the maximal possible size by running
 <code>resize2fs(8)</code> without specifying the new size. </p>
 
+SUBSECTION(«Fast Commits»)
+
+<p>
+
+Optimization introduced in 2020 (Linux-5.10).
+
+activated at mkfs time
+
+light-weight journaling method
+
+Idea: parts of the metadata written to the log can instead be derived
+from the inode. Leads to more compact format.
+
+Implementation: additional journal for fast commits, i.e., for those
+operations that can be optimized. Contains changes at the *file* level
+
+<li> Check <code>/proc/fs/ext4/dev/fc_info</code> to see whether fast
+commits are supported in the runing kernel. </li>
+
+</p>
+
 EXERCISES()
 
 <ul>