Re: [PATCH 00/13] convert block layer to bioset_init()/mempool_init()

[Kent Overstreet <kent.overstreet@gmail.com>]

On Mon, May 21, 2018 at 02:24:32PM -0400, Mike Snitzer wrote:
> Every single data structure change in this series should be reviewed for
> unforeseen alignment consequences.  Jens seemed to say that is
> worthwhile.  Not sure if he'll do it or we divide it up.  If we divide
> it up a temp topic branch should be published for others to inspect.
> 
> Could be alignment hasn't been a historic concern for a bunch of the
> data structures changed in this series.. if so then all we can do is fix
> up any obvious potential for false sharing.

Honestly, I almost never worry about alignment... the very few times I do care,
I use __cacheline_aligned_in_smp.

If alignment is a concern in any of those structs, there really ought to be a
comment indicating it. I very much doubt anything I touched was performance
sensitive enough for it to be an issue, though. And if there is a performance
impact, it should be oughtweighed by the reduced pointer chasing.

If you disagree, I don't mind leaving the device mapper patch out, it really
makes no difference to me. I could glance over for alignment issues but I feel
like my analysis would not be terribly valuable to you considering I've already
said my position on alignment is "meh, don't care" :)