On Thu, Jan 27, 2022 at 10:56:05AM +0200, Mike Rapoport wrote: > From: Mike Rapoport <rppt@xxxxxxxxxxxxx> > > Hi, > > This is a second attempt to make page allocator aware of the direct map > layout and allow grouping of the pages that must be mapped at PTE level in > the direct map. > Hello mike, It may be a silly question... Looking at implementation of set_memory*(), they only split PMD/PUD-sized entries. But why not _merge_ them when all entries have same permissions after changing permission of an entry? I think grouping __GFP_UNMAPPED allocations would help reducing direct map fragmentation, but IMHO merging split entries seems better to be done in those helpers than in page allocator. For example: 1) set_memory_ro() splits 1 RW PMD entry into 511 RW PTE entries and 1 RO PTE entry. 2) before freeing the pages, we call set_memory_rw() and we have 512 RW PTE entries. Then we can merge it to 1 RW PMD entry. 3) after 2) we can do same thing about PMD-sized entries and merge them into 1 PUD entry if 512 PMD entries have same permissions. [...] > Mike Rapoport (3): > mm/page_alloc: introduce __GFP_UNMAPPED and MIGRATE_UNMAPPED > mm/secretmem: use __GFP_UNMAPPED to allocate pages > EXPERIMENTAL: x86/module: use __GFP_UNMAPPED in module_alloc > > arch/Kconfig | 7 ++ > arch/x86/Kconfig | 1 + > arch/x86/kernel/module.c | 2 +- > include/linux/gfp.h | 13 +++- > include/linux/mmzone.h | 11 +++ > include/trace/events/mmflags.h | 3 +- > mm/internal.h | 2 +- > mm/page_alloc.c | 129 ++++++++++++++++++++++++++++++++- > mm/secretmem.c | 8 +- > 9 files changed, 162 insertions(+), 14 deletions(-) > > > base-commit: e783362eb54cd99b2cac8b3a9aeac942e6f6ac07 > -- > 2.34.1 > -- Thanks, Hyeonggon
