delay initializing queue for request-based dm

Hi

Currently for device-mapper devices, we initialize the mempool for requests and elevator at device creation time. But only request-based devices use the elevator and mempool. These patches change it to allocate the mempool and initialize the elevator only for request-based devices. This is done by allocating a queue at device creation time, but delaying the initialization of elevator and allocation of mempool till the first table load time, when the type of device would be known.

[PATCH 1/2] Allow delaying initialization of queue after allocation

[PATCH 2/2] Initialize mempool and elevator only for request-based dm devices

Another approach would be to free the mempool and detach elevator, if it would be a bio-based device. But it is better to avoid initialization itself.

Quoted 15 lines · On Saturday 08 August 2009 10:25:53 Nikanth Karthikesan wrote:

Hi

Currently for device-mapper devices, we initialize the mempool for requests and elevator at device creation time. But only request-based devices use the elevator and mempool. These patches change it to allocate the mempool and initialize the elevator only for request-based devices. This is done by allocating a queue at device creation time, but delaying the initialization of elevator and allocation of mempool till the first table load time, when the type of device would be known.

[PATCH 1/2] Allow delaying initialization of queue after allocation

[PATCH 2/2] Initialize mempool and elevator only for request-based dm devices

Quoted 3 lines

Another approach would be to free the mempool and detach elevator, if it would be a bio-based device. But it is better to avoid initialization itself.

Changes since v1:
1. Refreshed on top of a4e7d46407d73f35d217013b363b79a8f8eafcaa
2. Added comments suggested by Mike Snitzer.
3. Cleaned up the second patch as suggested by Mike Snitzer.