On Tue, Dec 7, 2021 at 4:51 PM Michal Hocko <mhocko@xxxxxxxx> wrote: > > On Fri 03-12-21 22:27:10, Alexey Avramov wrote: > > >I'd also like to know where that malfunction happens in this case. > > > > User-space processes need to always access shared libraries to work. > > It can be tens or hundreds of megabytes, depending on the type of workload. > > This is a hot cache, which is pushed out and then read leads to thrashing. > > There is no way in the kernel to forbid evicting the minimum file cache. > > This is the problem that the patch solves. And the malfunction is exactly > > that - the inability of the kernel to hold the minimum amount of the > > hottest cache in memory. > > Executable pages are a protected resource already page_check_references. > Shared libraries have more page tables pointing to them so they are more > likely to be referenced and thus kept around. What is the other memory > demand to push those away and cause a trashing? I've heard a lot of complaints that shared libraries can be swapped out and thrashing. it seems page_check_references won't be able to relieve the thrashing for them. on the other hand, exec pages could have a very big mapcount, that means reverse mapping of them will take a lot of time while they are reclaimed, so this makes the user experience even much worse while memory is under high pressure. Are we actually able to make mapcount a factor for memory reclaim in some way? The difficulty might be that a big mapcount doesn't necessarily mean the page is active. for For example, all processes mapping the page might be inactive. but reclaiming pages with a big mapcount has been a big pain as far as i know. Thanks Barry
