On Tue 24-05-22 08:52:02, CGEL wrote: > On Thu, May 19, 2022 at 09:39:57AM +0200, Michal Hocko wrote: > > On Thu 19-05-22 06:35:03, CGEL wrote: > > > On Wed, May 18, 2022 at 02:14:28PM +0200, Michal Hocko wrote: > > > > On Wed 18-05-22 07:40:30, CGEL wrote: > > > > [...] > > > > > 2. process_madvise is still a kind of madvise. processs_madvise from > > > > > another process overrides the intention of origin app code ifself that > > > > > also calls madvise, which is unrecoverable. For example, if a process "A" > > > > > which madvises just one part of VMAs (not all) as MERGEABLE run on the OS > > > > > already, meanwhile, if another process which doesn't know the information > > > > > of "A" 's MERGEABLE areas, then call process_madvise to advise all VMAs of > > > > > "A" as MERGEABLE, the original MERGEABLE information of "A" calling madivse > > > > > is erasured permanently. > > > > > > > > I do not really follow. How is this any different from an external > > > > process modifying the process wide policy via the proc or any other > > > > interface? > > > > > > In this patch, you can see that we didn't modify the flag of any VMA of > > > the target process, which is different from process_madvise. So it is > > > easy to keep the original MERGEABLE information of the target process > > > when we turn back to the default state from the state "always". > > > > This means that /proc/<pid>/smaps doesn't show the real state, right? > > Maybe we can add extra information of KSM forcible state in /proc/<pid>/smaps > like THPeligible. That information is already printed and I do not think that adding another flag or whatever would make the situation much more clear. > Really, Michal, I think it again, 'process_ madvise' is really not good. In > addition to some shortcomings I said before, If new vmas of the target process > are created after the external process calls process_madvise(), then we have to > call `process_madvise()` on them again, over and over again, regularly, just like > Oleksandr said [1]. I can see that this is not the most convenient way but so far I haven't really heard any arguments that this would be impossible. Look, I am not claiming that process_madvise is the only way to achieve the goal. I really do not like the proc based interface because it is rather adhoc and limited. We have other means to set a process wide property and I do not see any strong arguments agaist prctl. But more importantly I haven't really seen any serious analysis whether per-process (resp. per MM) property is even a desirable interface. Especially in the current form when opting out for certain VMAs is not possible. > [1]: https://lore.kernel.org/lkml/1817008.tdWV9SEqCh@xxxxxxxxxxxxxx/ -- Michal Hocko SUSE Labs
