[lkml]   [2001]   [Jan]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [RFC] ext2_new_block() behaviour
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?" -- Dogbert
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
Please read the FAQ at

 \ /
  Last update: 2005-03-22 12:52    [W:0.221 / U:0.008 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site