The size of the in-memory Imap should be (n + 255) / 256 * 4 bytes to store the mapping for all inodes.
Based on the total number of segments s of the disk,
The size of the in-memory SegTable should be (s + 7) / 8 bytes to store the mapping for all segments.
The problem is, n or s are not known at compile time, and hence, the size of the in-memory Imap or SegTable are also not known at compile time. Note that the Ufs also had a similar problem and solved this by limiting the max number of inodes to 200 for all disks.
To solve this, we should
Allocate the Imap and SegTable at a page instead of placing it on the Kernel. (At booting or every time we mount a disk)
Make the Imap or SegTable big enough so that any n or s should work.
We should have a reasonable limit for n or s.
This could be a small waste of memory if n or b is actually small for the disk.
In Lfs,
n,Imapshould be(n + 255) / 256 * 4bytes to store the mapping for all inodes.sof the disk,SegTableshould be(s + 7) / 8bytes to store the mapping for all segments.The problem is,
norsare not known at compile time, and hence, the size of the in-memoryImaporSegTableare also not known at compile time. Note that the Ufs also had a similar problem and solved this by limiting the max number of inodes to 200 for all disks.To solve this, we should
ImapandSegTableat a page instead of placing it on theKernel. (At booting or every time we mount a disk)ImaporSegTablebig enough so that anynorsshould work.nors.norbis actually small for the disk.