Re: Freeing page flags

[Josef Bacik <josef@toxicpanda.com>]

On Fri, May 13, 2022 at 04:39:28AM +0100, Matthew Wilcox wrote:
> On Thu, May 12, 2022 at 10:41:41PM -0400, Josef Bacik wrote:
> > On Thu, May 12, 2022 at 09:54:59PM +0100, Matthew Wilcox wrote:
> > > The LWN writeup [1] on merging the MGLRU reminded me that I need to send
> > > out a plan for removing page flags that we can do without.
> > > 
> > > 1. PG_error.  It's basically useless.  If the page was read successfully,
> > > PG_uptodate is set.  If not, PG_uptodate is clear.  The page cache
> > > doesn't use PG_error.  Some filesystems do, and we need to transition
> > > them away from using it.
> > >
> > 
> > What about writes?  A cursory look shows we don't clear Uptodate if we fail to
> > write, which is correct I think.  The only way to indicate we had a write error
> > to check later is the page error.
> 
> On encountering a write error, we're supposed to call mapping_set_error(),
> not SetPageError().
> 

Yup I can't read, the places I was looking did mapping_set_error() in a
different area from SetPageError() so I got confused, so this can be ripped out
of btrfs with no problems.  Thanks,

Josef