Re: [dm-devel] New -udm?

[Mike Christie <mikenc us ibm com>]

Lars Marowsky-Bree wrote:
> On 2005-04-11T02:27:11, Mike Christie <mikenc us ibm com> wrote:
>
>
> > what is wrong with what you have now where you utilize the queue/path's 
> > mempool by doing a blk_get_request with GFP_WAIT? 
>
>
> ... what if it's trying to free memory by going to swap on multipath,
> and can't, because we're blocked on getting the request with
> GFP_WAIT...?

GFP_WAIT does not casue IOs though. That is the difference between 
waiing on GFP_KERNEL and GFP_WAIT I thought. GFP_KERNEL can cause a page 
write out which you wait on and then there is a problem since it could 
be to the same disk you are trying to recover. But if you are just 
waiting for something to be returned to the mempool like with GFP_WAIT + 
blk_get_request you should be ok as long as the code below you 
eventually give up their resources and frees the requests you are 
waiting on?

> Your patch helps, because it means we need less memory.
>
> But, ultimately, we ought to preallocate the requests already when the
> hw-handler is initialized for a map (because presumably at that time
> we'll have enough memory, or can just fail the table setup). From that
> point on, our memory useage should not grow.
>
>
> Sincerely,
>     Lars Marowsky-Brée <lmb suse de>