Re: [PATCH] fbdev: fix incorrect address computation in deferred IO

[Nam Cao]

On Tue, Apr 23, 2024 at 01:27:09PM +0200, Thomas Zimmermann wrote:
> Am 23.04.24 um 11:55 schrieb Nam Cao:
..
> > > The page-fault handler at [1] use vm_fault.pgoff to retrieve the page
> > > structure. Can we do the same here and avoid that computation?
> > Yes, thanks for the suggestion.
> > 
> > It will change things a bit: offset will not be the exact value anymore,
> > but will be rounded down to multiple of PAGE_SIZE. But that doesn't matter,
> > because it will only be used to calculate the page offset later on.
> > 
> > We can clean this up and rename this "offset" to "pg_offset". But that's
> > for another day.
> 
> But can't we use struct vm_fault.pgoff directly? The page-fault handler has
> used it since forever. The look-up code for the pageref should probably do
> the same, because there's a 1:1 connection between the page and the pageref.
> The pageref structure only exists because we cannot store its data in struct
> page directly.
> 
> AFAICT pgoff is exactly the value want to compute. See [1] and  the
> calculation at [2].

Completely agree. I just wanted to point out that the value inside the
variable "offset" won't be the same as before, but it's still correct.

I just tested the patch on real hardware, will send it shortly.

Best regards,
Nam