Re: [PATCH 2/2] blk-mq-dma: bring back p2p request flags

[Christoph Hellwig <hch@lst.de>]

On Tue, Sep 02, 2025 at 08:36:51AM -0600, Keith Busch wrote:
> > We are actually about to run out of REQ_* bits with the current
> > encoding.  We could shrink the space for REQ_OP_ a bit to create
> > more, or try to move some flags out into BIO_ flags (like
> > REQ_ALLOC_CACHE) or kill them by looking at pointers instead
> > (REQ_INTEGRITY), or by overlaying flags that can't be used with
> > the same of (REQ_FUA vs REQ_RAHEAD vs REQ_UNMAP for example).
> > And maybe we can come up with a more coherent scheme for
> > REQ_PRIO / REQ_BACKGROUND / REQ_SWAP and maybe REQ_IDLE that create
> > another priority scheme in addition to the I/O priorities.
>  
> Sure, but can we do that effort separately from this? I'm mainly trying
> to align with Leon's DMA series that adds REQ_MMIO so that we won't have
> flag conflicts.

I was just thinking out aloud how we could reclaim them, not trying
to take that on for this series.