On Mon 11-09-23 14:12:26, Michal Hocko wrote: > On Mon 11-09-23 18:49:06, zhaoyang.huang wrote: > > From: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx> > > > > There will be redundant clear page within vma_alloc_zeroed_movable_folio > > when CONFIG_INIT_ON_ALLOC_DEFAULT_ON is on. Remove it by judging related > > configs. > > Thanks for spotting this. I suspect this is a fix based on a code review > rather than a real performance issue, right? It is always good to > mention that. From a very quick look it seems that many architectures > just definte vma_alloc_zeroed_movable_folio to use __GFP_ZERO so they > are not affected by this. This means that only a subset of architectures > are really affected. This is an important information as well. > Finally I think it would be more appropriate to mention that the double > initialization is done when init_on_alloc is enabled rather than > referring to the above config option which only controls whether the > functionality is enabled by default. > > I would rephrase as follows: > Many architectures (alpha, arm64, ia64, m68k s390, x86) define their own > vma_alloc_zeroed_movable_folio implementations which use __GFP_ZERO for > the page allocation. > > Those which rely on the default implementation, however, would currently > go through the initialization twice (oce in the page allocator and > second in vma_alloc_zeroed_movable_folio) if init_on_alloc is enabled > though. Fix this by checking want_init_on_alloc before calling > clear_user_highpage. Btw. have you checked other places which could have a similar problem? >From a very quick look __do_huge_pmd_anonymous_page, hugetlb_no_page, hugetlbfs_fallocate and shmem_mfill_atomic_pte all follow the same pattern. They do allocate memory so they go through the initialization in the allocator and then reinitialized. -- Michal Hocko SUSE Labs
