Re: dm: add support for DM_TARGET_NOWAIT for various targets

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On 11/12/20 2:05 PM, JeffleXu wrote:

dm-table.c:dm_table_set_restrictions() has:

         if (dm_table_supports_nowait(t))
                 blk_queue_flag_set(QUEUE_FLAG_NOWAIT, q);
         else
                 blk_queue_flag_clear(QUEUE_FLAG_NOWAIT, q);

This patch adds support for DM_TARGET_NOWAIT for those dm targets, the
.map() algorithm of which just involves sector recalculation.
So you're looking to constrain which targets will properly support
REQ_NOWAIT, based on whether they do a simple remapping?

To be honest, I'm a little confused about the semantics of REQ_NOWAIT. Jens may had ever

explained it in block or io_uring mailing list, but I can't find the specific mail.

I find it here https://lore.kernel.org/linux-block/f1a6ae88-1436-e947-1124-41e10b3ea9bc@xxxxxxxxx/


So if the IO is offloaded to workqueue and the current process context will not get blocked,

then is this device capable of handling REQ_NOWAIT or not?

--
Thanks,
Jeffle

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