Revert "fs: do not prefault sys_write() user buffer pages"
This reverts commit 998ef75d . The commit itself does not appear to be buggy per se, but it is exposing a bug in ext4 (and Ted thinks ext3 too, but we solved that by getting rid of it). It's too late in the release cycle to really worry about this, even if Dave Hansen has a patch that may actually fix the underlying ext4 problem. We can (and should) revisit this for the next release. The problem is that moving the prefaulting later now exposes a special case with partially successful writes that isn't handled correctly. And the prefaulting likely isn't normally even that much of a performance issue - it looks like at least one reason Dave saw this in his performance tests is that he also ran them on Skylake that now supports the new SMAP code, which makes the normally very cheap user space prefaulting noticeably more expensive. Bisected-and-acked-by: Ted Ts'o <firstname.lastname@example.org> Analyzed-and-acked-by: Dave Hansen <email@example.com> Cc: Andrew Morton <firstname.lastname@example.org> Signed-off-by: Linus Torvalds <email@example.com>
Showing with 16 additions and 18 deletions