On Mon, Jun 10, 2024 at 06:50:11AM +0930, Qu Wenruo wrote: > Hi, > > There is a recent (well a year ago) change in btrfs to remove the usage > of page/folio error, which gets me wondering what would happen if we got > a lot of write errors and high memory pressure? > > Yes, all file systems calls mapping_set_error() so that fsync call would > return error, but I'm wondering what would happen to those folios that > failed to be written? > > Those folios has their DIRTY flag cleared before submission, and and > their endio functions, the WRITEBACK flags is also cleared. > > Meaning after such write failure, the page/folio has UPTODATE flag, and > no DIRTY/ERROR/WRITEBACK flags (at least for btrfs and ext4, meanwhile > iomap still set the ERROR flag). > > Would any memory pressure just reclaim those pages/folios without them > really reaching the disk? Yes. Core code doesn't (and hasn't in some time) checked the page/folio error flag. That's why it's being removed. Also, btrfs was using it incorrectly to indicate a write error. It was supposed to be used for read errors, not write errors. Another good reason to remove it.
