Walking the Superblocks
When mappings are written back inode-by-inode, the initial path taken is via all system superblock instances that represent the mounted filesystems. sync_sb_inodes is invoked for each instance in order to write back the superblock inode data, as shown in the code flow diagram in Figure 17-6. Walking the superblock list can be terminated by two different conditions:
1. All superblock instances have been scanned sequentially. The kernel has reached the end of the list, and its work is therefore done.
2. The maximum number of writeback pages specified by the writeback_control instance has been reached. Since writeback requires obtaining various important locks, the system should not be disturbed for too long to make the inodes available for other parts of the kernel again.
Continue reading here: Examining Superblock Inodes
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