Re: [PATCH 1/2] zram: remove BD_CAP_SYNCHRONOUS_IO with writeback feature

Sergey Senozhatsky
2018-08-03T02:52:37Z

On (08/03/18 11:39), Sergey Senozhatsky wrote:
> [..]
>
> > A reader looking at this would wonder "why the heck are we doing that".
> > Adding a code comment would help them.
>
> The interesting thing here is that include/linux/backing-dev.h
> BDI_CAP_SYNCHRONOUS_IO comment says
>
> "Device is so fast that asynchronous IO would be inefficient."
>
> Which is not the reason why BDI_CAP_SYNCHRONOUS_IO is used by ZRAM.
> Probably, the comment needs to be updated as well.
>
> Both SWP_SYNCHRONOUS_IO and BDI_CAP_SYNCHRONOUS_IO tend to pivot
> "efficiency" [looking at the comments], but in ZRAM's case the whole
> reason to use SYNC IO is a race condition and user-after-free that
^ASYNC IO

-ss