Re: Linux MD RAID5/6 bitmap patches

[Paul Clements <paul.clements@steeleye.com>]

Yogesh Pahilwan wrote:

> Thanks for your reply. As far as what I understood that when we apply the
> bitmap patch, for every write it will do 2 sync writes that is setting the
> dirty bit, writing intent log and one async write for clearing the dirty
> bit. Is it correct?

The bits are in the intent log, so the "setting dirty bit" and "writing 
intent log" are the same thing. Just one write.

> If that is the case are there any patches available which can do collection
> of sync write in a queue and write a collection in single write request.
> For Eg:
> For 10 writes , we will have 10 + 1 sync writes + 10 async write.

The bitmap code already does this by default. The bitmap writes are 
queued up so that all writes to a given page (within a short time 
period) are reduced to a single write. The performance is actually quite 
good. There's very little performance difference between having a bitmap 
versus not having one.

> I mean to say , 10 sync writes for setting the dirty bits + 1 sync write for
> write intent log for all queued request in one write operation + 10 async
> write for clearing the dirty bit.

The async writes for clearing the bitmap are also combined.

--
Paul