[lkml]   [2006]   [Nov]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: [dm-devel] [RFC][PATCH] dm-cache: block level disk cache target for device mapper
On Thursday 30 November 2006 17:24, Eric Van Hensbergen wrote:
> On 11/30/06, Jens Wilke <> wrote:
> > On Monday 27 November 2006 19:26, Eric Van Hensbergen wrote:
> >
> > If this is intended to speed up remote disks, is it possible that the cache content
> > can be paged out on local disks in low-mem situations?
> >
> The main intent was to use local disks as cache to offload centralized
> remote disks. The logic was that most systems have local disks, if
> only for swap -- so why not use them as a cache to help offload
> centralized storage. While the in-memory page cache works perfectly
> fine in certain situations -- we were dealing with workloads in which
> the in-memory page-cache wasn't sufficient to hold all the data.

I derived from the code that the cache is actually another block device
and not memory. Maybe you should give a little more description and
a sample 'dmsetup create' statement.

> There are also some additional possibilities we've thought through and
> have been playing with including allowing the local disk cache to be
> persistent across reboots (with varying validation schemes).

Yes, I like the idea. It would be also possible to use NV-Ram
as write back cache, for example in notebooks, to avoid
disk spin-ups or to improve transaction performance in
enterprise applications.

Maybe it would also make sense to prefill the cache contents
on startup with a bulk I/O request?

Comments on the code:

- The data of the write back cache should be flushed on suspend and not
in the destructor.
- You don't keep track of I/O on the fly to the cache that is mapped
directly in cache_hit(). How do you make sure that this I/O is completed
before you replace a cache block?
- The cache block index is hashed, this means the cache data blocks are not
clustered. I don't think you can solve this problem with a proper hash function.
Perhaps you should consider a (B-)Tree structure for that.


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: 2006-11-30 21:11    [W:0.095 / U:1.508 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site