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FreeBSD's boot times have decreased to the point where vm_page array initialization represents a significant fraction of the total boot time. For example, when booting FreeBSD in Firecracker (a VMM designed to support lightweight VMs) with 128MB and 1GB of RAM, vm_page initialization consumes 9% (3ms) and 37% (21.5ms) of the kernel boot time, respectively. This is generally relevant in cloud environments, where one wants to be able to spin up VMs as quickly as possible. This patch implements lazy initialization of (most) page structures, following a suggestion from cperciva@. The idea is to introduce a new free pool, VM_FREEPOOL_LAZYINIT, into which all vm_page structures are initially placed. For this to work, we need only initialize the first free page of each chunk placed into the buddy allocator. Then, early page allocations draw from the lazy init pool and initialize vm_page chunks (up to 16MB, 4096 pages) on demand. Once APs are started, an idle-priority thread drains the lazy init pool in the background to avoid introducing extra latency in the allocator. With this scheme, almost all of the initialization work is moved out of the critical path. A couple of vm_phys operations require the pool to be drained before they can run: vm_phys_find_range() and vm_phys_unfree_page(). However, these are rare operations. I believe that vm_phys_find_freelist_contig() does not require any special treatment, as it only ever accesses the first page in a power-of-2-sized free page chunk, which is always initialized. For now the new pool is only used on amd64 and arm64, since that's where I can easily test and those platforms would get the most benefit. Reviewed by: alc, kib Differential Revision: https://reviews.freebsd.org/D40403 |
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| .. | ||
| _vm_phys.h | ||
| _vm_radix.h | ||
| device_pager.c | ||
| memguard.c | ||
| memguard.h | ||
| phys_pager.c | ||
| pmap.h | ||
| redzone.c | ||
| redzone.h | ||
| sg_pager.c | ||
| swap_pager.c | ||
| swap_pager.h | ||
| uma.h | ||
| uma_align_mask.h | ||
| uma_core.c | ||
| uma_dbg.c | ||
| uma_dbg.h | ||
| uma_int.h | ||
| vm.h | ||
| vm_domainset.c | ||
| vm_domainset.h | ||
| vm_dumpset.h | ||
| vm_extern.h | ||
| vm_fault.c | ||
| vm_glue.c | ||
| vm_init.c | ||
| vm_kern.c | ||
| vm_kern.h | ||
| vm_map.c | ||
| vm_map.h | ||
| vm_meter.c | ||
| vm_mmap.c | ||
| vm_object.c | ||
| vm_object.h | ||
| vm_page.c | ||
| vm_page.h | ||
| vm_pageout.c | ||
| vm_pageout.h | ||
| vm_pagequeue.h | ||
| vm_pager.c | ||
| vm_pager.h | ||
| vm_param.h | ||
| vm_phys.c | ||
| vm_phys.h | ||
| vm_radix.c | ||
| vm_radix.h | ||
| vm_reserv.c | ||
| vm_reserv.h | ||
| vm_swapout.c | ||
| vm_swapout_dummy.c | ||
| vm_unix.c | ||
| vnode_pager.c | ||
| vnode_pager.h | ||