On Fri, Aug 26, 2022 at 10:53:46AM -0700, Minchan Kim wrote: > Long term, that's better idea(For stable backport, I'd like to go with > simple PageLRU check). > > I wonder it's possible to mix LRU pages and non-struct pages together > in a VMA. Otherwise, could we reuse(abuse) VM_MIXEDMAP? On a bit of a tangent, I'm not sure that we should be allowing this for file pages at all. I see that we only allow it if mapcount is 1, but page cache is also used by applications that don't mmap it. So if some other application is using /tmp/bigfile with read() and write(), I can force that memory out of the page cache by mmaping it and calling MADV_PAGEOUT. That could be used as an exfiltration side-channel, for example.
