On Tue, 24 Apr 2018, Michal Hocko wrote:
> On Mon 23-04-18 20:25:15, Mikulas Patocka wrote: > > > Fixing __vmalloc code > > is easy and it doesn't require cooperation with maintainers. > > But it is a hack against the intention of the scope api. It is not! You can fix __vmalloc now and you can convert the kernel to the scope API in 4 years. It's not one way or the other. > It also alows maintainers to not care about their broken code. Most maintainers don't even know that it's broken. Out of 14 subsystems using __vmalloc with GFP_NOIO/NOFS, only 2 realized that its implementation is broken and implemented a workaround (me and the XFS developers). Misimplementing a function in a subtle and hard-to-notice way won't drive developers away from using it. > > > > He refuses 15-line patch to fix GFP_NOIO bug because he believes that > > > > in 4 > > > > years, the kernel will be refactored and GFP_NOIO will be eliminated. > > > > Why > > > > does he have veto over this part of the code? I'd much rather argue > > > > with > > > > people who have constructive comments about fixing bugs than with him. > > > > > > I didn't NACK the patch AFAIR. I've said it is not a good idea longterm. > > > I would be much more willing to change my mind if you would back your > > > patch by a real bug report. Hacks are acceptable when we have a real > > > issue in hands. But if we want to fix potential issue then better make > > > it properly. > > > > Developers should fix bugs in advance, not to wait until a crash hapens, > > is analyzed and reported. > > I agree. But are those existing users broken in the first place? I have > seen so many GFP_NOFS abuses that I would dare to guess that most of > those vmalloc NOFS abusers can be simply turned into GFP_KERNEL. Maybe > that is the reason we haven't heard any complains in years. alloc_pages reclaims clean pages and most hard work is done by kswapd, so GFP_KERNEL doesn't cause much issues with writeback. But cheating isn't justified if you can get away with it. Incorrect GFP flags cause real problems with shrinkers - because shrinkers are called from alloc_pages and they do respond to GFP flags. I had reported deadlock due to GFP issues (9d28eb12447). And the worst thing about these bug reports is that they are totally unreproducible and I get nothing, but a stacktrace in bugzilla. I had to guess what happened and I couldn't even test if the patch fixed the bug. I'm not really happy that you are deliberately leaving these issues behind and making excuses. Mikulas
