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. > 2. PG_private. This tells us whether we have anything stored at > page->private. We can just check if page->private is NULL or not. > No need to have this extra bit. Again, there may be some filesystems > that are a bit wonky here, but I'm sure they're fixable. > At least for Btrfs we serialize the page->private with the private_lock, so we could probably just drop PG_private, but it's kind of nice to check first before we have to take the spin lock. I suppose we can just do if (page->private) // do lock and check thingy Thanks, Josef
