Re: [RFC] block: Make MMC respect REQ_NOUNMAP?

[Christoph Hellwig]

On Wed, May 07, 2025 at 06:24:34PM +0200, Ahmad Fatoum wrote:
>     blk_ioctl_zeroout
>         blkdev_issue_zeroout(..., BLKDEV_ZERO_NOUNMAP)
>             __blkdev_issue_write_zeroes(..., BLKDEV_ZERO_NOUNMAP)
> 	    submit_bio_wait(bio->bi_opf = REQ_NOUNMAP)
> 
> __REQ_NOUNMAP has comment saying 'do not free blocks when zeroing',
> but as shown above, TRIM allows the card to unmap the indicated region.

__REQ_NOUNMAP is a hint.  All the storage specs are a mess in this
area as they usually get the polarity wrong and/or just have very
vague semantics.  Also actually writing zeroes and not unmapping is
totally pointless on flash storage as it just increases PE cycles
for no good reason.