0fbb4d93b3
Where possible, switch from early bio-based IO accounting (at the time DM clones each incoming bio) to late IO accounting just before each remapped bio is issued to underlying device via submit_bio_noacct(). Allows more precise bio-based IO accounting for DM targets that use their own workqueues to perform additional processing of each bio in conjunction with their DM_MAPIO_SUBMITTED return from their map function. When a target is updated to use dm_submit_bio_remap() they must also set ti->accounts_remapped_io to true. Use xchg() in start_io_acct(), as suggested by Mikulas, to ensure each IO is only started once. The xchg race only happens if __send_duplicate_bios() sends multiple bios -- that case is reflected via tio->is_duplicate_bio. Given the niche nature of this race, it is best to avoid any xchg performance penalty for normal IO. For IO that was never submitted with dm_bio_submit_remap(), but the target completes the clone with bio_endio, accounting is started then ended and pending_io counter decremented. Reviewed-by: Mikulas Patocka <mpatocka@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> |
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