On Wed, Apr 27, 2022 at 1:59 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: > > On Mon, Apr 04, 2022 at 05:48:49PM -0700, Yang Shi wrote: > > When khugepaged collapses file THPs, its behavior is not consistent. > > It is kind of "random luck" for khugepaged to see the file vmas (see > > report: https://lore.kernel.org/linux-mm/00f195d4-d039-3cf2-d3a1-a2c88de397a0@xxxxxxx/) > > since currently the vmas are registered to khugepaged when: > > - Anon huge pmd page fault > > - VMA merge > > - MADV_HUGEPAGE > > - Shmem mmap > > > > If the above conditions are not met, even though khugepaged is enabled > > it won't see any file vma at all. MADV_HUGEPAGE could be specified > > explicitly to tell khugepaged to collapse this area, but when > > khugepaged mode is "always" it should scan suitable vmas as long as > > VM_NOHUGEPAGE is not set. > > I don't see that as being true at all. The point of this hack was that > applications which really knew what they were doing could enable it. > It makes no sense to me that setting "always" by the sysadmin for shmem > also force-enables ROTHP, even for applications which aren't aware of it. > > Most telling, I think, is that Song Liu hasn't weighed in on this at > all. It's clearly not important to the original author. Song Liu already acked the series, please see https://lore.kernel.org/linux-mm/96F2D93B-2043-44C3-8062-C639372A0212@xxxxxx/
