On Tue, Nov 22 2016, Shaohua Li wrote: > On Mon, Nov 21, 2016 at 12:19:43PM +1100, Neil Brown wrote: >> There are 2 problems with using bi_phys_segments as a counter >> 1/ we only use 16bits, which limits bios to 256M >> 2/ it is poor form to reuse a field like this. It interferes >> with other changes to bios. >> >> We need to clean up a few things before we can change the use the >> counter which is now available inside a bio. >> >> I have only tested this lightly. More review and testing would be >> appreciated. > > So without the accounting, we: > - don't do bio completion trace Yes, but hopefully that will be added back to bio_endio() soon. > - call md_write_start/md_write_end excessively, which involves atomic operation. raid5_inc_bio_active_stripes() did an atomic operation. I don't think there is a net increase in the number of atomic operations. > > Not big problems. But we are actually reusing __bi_remaining, I'm wondering why > we not explicitly reuse it. Eg, adds bio_dec_remaining_return() and uses it > like raid5_dec_bi_active_stripes. Because using it exactly the same way that other places use it leads to fewer surprises, now or later. And I think that the effort to rearrange the code so that we could just call bio_endio() brought real improvements in code clarity and simplicity. Thanks, NeilBrown
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