Hi Dev, On 04/09/2024 11:09, Dev Jain wrote: > It was observed at [1] and [2] that the current kernel behaviour of > shattering a hugezeropage is inconsistent and suboptimal. For a VMA with > a THP allowable order, when we write-fault on it, the kernel installs a > PMD-mapped THP. On the other hand, if we first get a read fault, we get > a PMD pointing to the hugezeropage; subsequent write will trigger a > write-protection fault, shattering the hugezeropage into one writable > page, and all the other PTEs write-protected. The conclusion being, as > compared to the case of a single write-fault, applications have to suffer > 512 extra page faults if they were to use the VMA as such, plus we get > the overhead of khugepaged trying to replace that area with a THP anyway. > > Instead, replace the hugezeropage with a THP on wp-fault. > > v1->v2: > - Wrap do_huge_zero_wp_pmd_locked() around lock and unlock > - Call thp_fault_alloc() before do_huge_zero_wp_pmd_locked() to avoid > - calling sleeping function from spinlock context > > [1]: https://lore.kernel.org/all/3743d7e1-0b79-4eaf-82d5-d1ca29fe347d@xxxxxxx/ > [2]: https://lore.kernel.org/all/1cfae0c0-96a2-4308-9c62-f7a640520242@xxxxxxx/ > > Dev Jain (2): > mm: Abstract THP allocation > mm: Allocate THP on hugezeropage wp-fault > > include/linux/huge_mm.h | 6 ++ > mm/huge_memory.c | 171 +++++++++++++++++++++++++++++----------- > mm/memory.c | 5 +- > 3 files changed, 136 insertions(+), 46 deletions(-) > What is the base for this? It doesn't apply on top of mm-unstable. Thanks, Ryan
