On Tue, 11 Feb 2025 16:43:09 +0530 Dev Jain <dev.jain@xxxxxxx> wrote: > This patchset extends khugepaged from collapsing only PMD-sized THPs to > collapsing anonymous mTHPs. > > mTHPs were introduced in the kernel to improve memory management by allocating > chunks of larger memory, so as to reduce number of page faults, TLB misses (due > to TLB coalescing), reduce length of LRU lists, etc. However, the mTHP property > is often lost due to CoW, swap-in/out, and when the kernel just cannot find > enough physically contiguous memory to allocate on fault. Henceforth, there is a > need to regain mTHPs in the system asynchronously. This work is an attempt in > this direction, starting with anonymous folios. > > In the fault handler, we select the THP order in a greedy manner; the same has > been used here, along with the same sysfs interface to control the order of > collapse. In contrast to PMD-collapse, we (hopefully) get rid of the mmap_write_lock(). > > --------------------------------------------------------- > Testing > --------------------------------------------------------- > > The set has been build tested on x86_64. > For Aarch64, > 1. mm-selftests: No regressions. > 2. Analyzing with tools/mm/thpmaps on different userspace programs mapping > aligned VMAs of a large size, faulting in basepages/mTHPs (according to sysfs), > and then madvise()'ing the VMA, khugepaged is able to 100% collapse the VMAs. It would be nice to provide some evidence that this patchset actually makes Linux better for our users, and by how much. Thanks, I think I'll skip v2 and shall await reviewer input.
