I am confused about "echo # >/proc/sys/vm/drop_caches" and blockdev --flushbufs. According to OSStep book written by Remzi,If the target inodes are not cached in memory, disk IO should be occur to readthe inode, which will make a dentry data structure on memory. To my knowledge, echo 3 >/proc/sys/vm/drop_caches is to drop(clear) page cahche, inodes and dentry. I have experimented with blktrace to figure out whether disk io is really occurring to read the inode. 1. echo 3 > /proc/sys/vm/drop_caches However, there is no disk io to read inode. I can only see the disk io to read 16KB data block. 2. echo 3 > /proc/sys/vm/drop_caches` and `blockdev --flushbufs /dev/nvme0n1I found block access (+8(512*8=4KB)) to read inode. A quick look at how blockdev --flushbufs works in the kernel code shows that it clears the superblock. Why doesn't disk io occur to read inodes with drop_cache alone? The kernel book called ULK says that inodes and superblocks are cached in buffer-cache.Is this the reason for this? I infer as follows:Is the buffer_head data structure not flushed to disk by drop_cache alone because the storage device is still mapped in memory? Thank you
