[lkml]   [2005]   [Jul]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: why is jiffies 128 in jffs2_find_gc_block() in gc.c of jffs2
On Fri, 2005-07-22 at 10:14 +0530, krishna wrote:
> I am not clear why the hardcoded values are 50, 110 and 126
> and why is jiffies moded with 128, why not any other value.

It's just a way to achieve 'randomness' which doesn't actually consume
entropy and which is quick to obtain. It only needs to be relatively
evenly distributed.

We use it for selecting the next eraseblock to be garbage-collected.
50/128 of the time we pick a block from the eraseable_list, 60/128 of
the time we pick a block from the very_dirty_list, 16/128 of the time we
pick a block from the dirty_list, and the remaining 2/128 of the time we
pick a block from the clean_list for garbage collection.

The precise numbers don't have a huge amount of science behind them;
they are mostly guesses about what would achieve evenly-distributed wear
levelling over time without garbage-collecting clean blocks more often
than is necessary.

If you want to conduct tests with various workloads in order to refine
the fairly primitive algorithm described above, that could be useful.


To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

 \ /
  Last update: 2005-07-22 17:59    [W:0.021 / U:4.760 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site