On 4/28/2026 7:21 AM, Benjamin Marzinski wrote:
> On Mon, Apr 27, 2026 at 01:23:27AM -0400, Benjamin Marzinski wrote:
>> On Fri, Apr 10, 2026 at 06:40:30AM -0700, Linlin Zhang wrote:
>>> From: Eric Biggers <[email protected]>
>>> + /*
>>> + * Since we've added an encryption context to the bio and
>>> + * blk-crypto-fallback may be needed to process it, it's necessary to
>>> + * use the fallback-aware bio submission code rather than
>>> + * unconditionally returning DM_MAPIO_REMAPPED.
>>> + *
>>> + * To get the correct accounting for a dm target in the case where
>>> + * __blk_crypto_submit_bio() doesn't take ownership of the bio (returns
>>> + * true), call __blk_crypto_submit_bio() directly and return
>>> + * DM_MAPIO_REMAPPED in that case, rather than relying on
>>> + * blk_crypto_submit_bio() which calls submit_bio() in that case.
>>> + */
>>> + if (__blk_crypto_submit_bio(bio))
>>
>> This will still double account for fallback writes (which call
>> submit_bio() on the encrypted bios, and return DM_MAPIO_SUBMITTED here).
>
> Just to clarify, I'm talking about the vmstats accounting. The IO
> originally gets accounted by submit_bio() when the bio is submitted to
> the dm device. For actual inline encryption and fallback reads, dm will
> submit the bio to the underlying device using submit_bio_noacct() to
> avoid double-counting the IO.
>
> For fallback writes, __blk_crypto_submit_bio() will submit the encrypted
> bios to the underlying device with submit_bio(). This adds the IO
> sectors again, even though it's the same IO, only encrypted now.
Right, thanks for calling this out.
For fallback writes, the IO is still double-counted. Given that this only
affects IO accounting in the blk-crypto fallback write slow-path and not
correctness, I think this is an acceptable tradeoff, and we can leave a
TODO to revisit the accounting once a better solution exists.
Add the bellow to the annotate.
/*
* TODO: blk-crypto fallback write slow-path currently double-accounts
* IO in vmstat, as encrypted bios are submitted via submit_bio().
* This does not affect data correctness. Consider fixing this if
* a cleaner accounting model for derived bios is introduced.
*/
Do you agree?
>
> -Ben
>
>>
>> -Ben
>>
>>> + return DM_MAPIO_REMAPPED;
>>> + return DM_MAPIO_SUBMITTED;
>>> +}
>>
>
