Messages in this thread |  | | From | Andreas Dilger <> | Subject | Re: [RFC] ext2_new_block() behaviour | Date | Tue, 2 Jan 2001 18:47:25 -0700 (MST) |
| |
Al, you write: > Folks, there is a pretty strange detail of the allocation policy - > if cylinder group has no free blocks past the goal ext2 tries very hard to > avoid allocation in the beginning of the group. I.e. order looks so: > > * goal > * goal .. (goal+63) & ~63 > * goal .. end of cylinder group > * cylinder groups past one that contains goal > * cylinder groups before one that contains goal > * beginning of cylinder group..goal-1 > > It looks somewhat fishy. What's the reason for such policy?
This predates me by a while, but I suspect that it is done this way on the assumption it is easier to seek forward on the disk while reading a file rather than seeking backwards. Also, since with new inodes the goal is initially the first block of the group where the inode lives, the blocks at the start of a group will generally be allocated already, so it is usually a waste of time checking the start of the group for free blocks.
Cheers, Andreas -- Andreas Dilger \ "If a man ate a pound of pasta and a pound of antipasto, \ would they cancel out, leaving him still hungry?" http://www-mddsp.enel.ucalgary.ca/People/adilger/ -- Dogbert - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org Please read the FAQ at http://www.tux.org/lkml/
|  |