Proposing this as a LSF/MM TOPIC, but it may turn out to be me just not understanding the semantics here. As I was looking into -ENOSPC handling in cephfs, I noticed that PG_error is only ever tested in one place [1] __filemap_fdatawait_range, which does this: if (TestClearPageError(page)) ret = -EIO; This error code will override any AS_* error that was set in the mapping. Which makes me wonder...why don't we just set this error in the mapping and not bother with a per-page flag? Could we potentially free up a page flag by eliminating this? The main argument I could see for keeping it is that removing it might subtly change the behavior of sync_file_range if you have tasks syncing different ranges in a file concurrently. I'm not sure if that would break any guarantees though. Even if we do need it, I think we might need some cleanup here anyway. A lot of readpage operations end up setting that flag when they hit an error. Isn't it wrong to return an error on fsync, just because we had a read error somewhere in the file in a range that was never dirtied? -- [1]: there is another place in f2fs, but it's more or less equivalent to the call site in __filemap_fdatawait_range. -- Jeff Layton <jlayton@xxxxxxxxxx>
