vm_phys_enqueue_contig: handle zero pages

[dougm]

Summary

By letting vm_phys_enqueue_contig handle the case when npages == 0, the callers can stop checking it, and the compiler can stop zero-checking with every call to ffs(). Letting vm_phys_enqueue_contig call vm_phys_enqueue_contig for part of its work also saves a few bytes.

The amd64 object code shrinks by 80 bytes.

Test Plan

Peter, can you test this please?

[dougm]

Take care in vm_phys_enqueue_contig to handle npages==0 and npages==1 properly.

[dougm]

Using objdump outputs to compare start addresses of vm_phys functions before and after this change

Before                                                          After
0000000000000090 <vm_phys_mem_affinity>:                        0000000000000090 <vm_phys_mem_affinity>:
00000000000000c0 <vm_phys_add_seg>:                             00000000000000c0 <vm_phys_add_seg>:
0000000000000130 <vm_phys_create_seg>:                          0000000000000130 <vm_phys_create_seg>:
0000000000000350 <vm_phys_init>:                                0000000000000350 <vm_phys_init>:
0000000000000870 <vm_phys_register_domains>:                    0000000000000870 <vm_phys_register_domains>:
0000000000000930 <vm_phys_alloc_npages>:                        0000000000000930 <vm_phys_alloc_npages>:
0000000000000f00 <vm_phys_alloc_pages>:                       | 0000000000000ec0 <vm_phys_alloc_pages>:
0000000000000f70 <vm_phys_alloc_freelist_pages>:              | 0000000000000f30 <vm_phys_alloc_freelist_pages>:
00000000000011d0 <vm_phys_paddr_to_vm_page>:                  | 0000000000001190 <vm_phys_paddr_to_vm_page>:
0000000000001250 <vm_phys_fictitious_to_vm_page>:             | 0000000000001210 <vm_phys_fictitious_to_vm_page>:
00000000000012c0 <vm_phys_fictitious_reg_range>:              | 0000000000001280 <vm_phys_fictitious_reg_range>:
0000000000001790 <vm_phys_fictitious_unreg_range>:            | 0000000000001750 <vm_phys_fictitious_unreg_range>:
0000000000001b50 <vm_phys_free_pages>:                        | 0000000000001b10 <vm_phys_free_pages>:
0000000000001cf0 <vm_phys_enqueue_contig>:                    | 0000000000001cb0 <vm_phys_enqueue_contig>:
0000000000001e90 <vm_phys_free_contig>:                       | 0000000000001e40 <vm_phys_free_contig>:
0000000000001f80 <vm_phys_find_range>:                        | 0000000000001f30 <vm_phys_find_range>:
0000000000002060 <vm_phys_unfree_page>:                       | 0000000000002010 <vm_phys_unfree_page>:
00000000000021f0 <vm_phys_alloc_contig>:                      | 00000000000021a0 <vm_phys_alloc_contig>:
0000000000002730 <vm_phys_avail_largest>:                     | 00000000000026e0 <vm_phys_avail_largest>:
0000000000002790 <vm_phys_avail_size>:                        | 0000000000002740 <vm_phys_avail_size>:
00000000000027b0 <vm_phys_is_dumpable>:                       | 0000000000002760 <vm_phys_is_dumpable>:
0000000000002890 <vm_phys_early_add_seg>:                     | 0000000000002840 <vm_phys_early_add_seg>:
00000000000028f0 <vm_phys_early_alloc>:                       | 00000000000028a0 <vm_phys_early_alloc>:
0000000000002b30 <vm_phys_avail_split>:                       | 0000000000002ae0 <vm_phys_avail_split>:
0000000000002ce0 <vm_phys_early_startup>:                     | 0000000000002c90 <vm_phys_early_startup>:
0000000000002f30 <sysctl_vm_phys_free>:                       | 0000000000002ee0 <sysctl_vm_phys_free>:
0000000000003120 <sysctl_vm_phys_segs>:                       | 00000000000030d0 <sysctl_vm_phys_segs>:
0000000000003220 <sysctl_vm_phys_locality>:                   | 00000000000031d0 <sysctl_vm_phys_locality>:

[dougm]

Make sure the right find-{first,last}-bit is invoked on addresses.

[dougm]

Fix, hopefully, the length parameter in the last call to vm_phys_enq_range.

[pho]

With D41154.125484.patch I now see:

igb0: <Intel(R) I350 (Copper)> port 0xd020-0xd03f mem 0xfb320000-0xfb33ffff,0xfb344000-0xfb347fff irq 16 at device 0.0 on pci8
igb0: EEPROM V1.63-0 eTrack 0x800009fa
igb0: Using 1024 TX descriptors and 1024 RX descriptors
igb0: queue equality override not set, capping rx_queues at 6 and tx_queues at 6
igb0: Usin
db> show panic
panic: vm_phys_enq_range: page 0xfffffe0002fd4c18 and npages 0 are misaligned
db> x/s version
version:        FreeBSD 14.0-CURRENT #0 main-n264491-8a5c836b51ce2-dirty: Thu Aug  3 06:23:37 CEST 2023\012    [e-mail]:/usr/sr
db> bt
Tracing pid 37 tid 100210 td 0xfffffe010e620900  
kdb_enter() at kdb_enter+0x32/frame 0xfffffe010db821f0
vpanic() at vpanic+0x17a/frame 0xfffffe010db82240
panic() at panic+0x43/frame 0xfffffe010db822a0
vm_phys_enq_range() at vm_phys_enq_range+0x11d/frame 0xfffffe010db822b0
vm_phys_alloc_npages() at vm_phys_alloc_npages+0x5a6/frame 0xfffffe010db82320
vm_page_zone_import() at vm_page_zone_import+0xa7/frame 0xfffffe010db82370
zone_alloc_item() at zone_alloc_item+0x78/frame 0xfffffe010db823c0
vm_page_alloc_domain_after() at vm_page_alloc_domain_after+0x151/frame 0xfffffe010db82450
vm_page_alloc() at vm_page_alloc+0x64/frame 0xfffffe010db824b0
vm_fault_allocate() at vm_fault_allocate+0x1a5/frame 0xfffffe010db82520
vm_fault() at vm_fault+0x448/frame 0xfffffe010db82650
vm_fault_trap() at vm_fault_trap+0x6f/frame 0xfffffe010db82690
trap_pfault() at trap_pfault+0x24a/frame 0xfffffe010db82700
calltrap() at calltrap+0x8/frame 0xfffffe010db82700
--- trap 0xc, rip = 0xffffffff8104db36, rsp = 0xfffffe010db827d0, rbp = 0xfffffe010db827d0 ---
copyout_nosmap_erms() at copyout_nosmap_erms+0x156/frame 0xfffffe010db827d0
elf64_load_sections() at elf64_load_sections+0x283/frame 0xfffffe010db82860
elf64_load_file() at elf64_load_file+0x280/frame 0xfffffe010db828c0
elf64_load_interp() at elf64_load_interp+0x67/frame 0xfffffe010db82900
exec_elf64_imgact() at exec_elf64_imgact+0xe01/frame 0xfffffe010db829f0
kern_execve() at kern_execve+0x772/frame 0xfffffe010db82d80
sys_execve() at sys_execve+0x58/frame 0xfffffe010db82e00
amd64_syscall() at amd64_syscall+0x14f/frame 0xfffffe010db82f30
fast_syscall_common() at fast_syscall_common+0xf8/frame 0xfffffe010db82f30
--- syscall (59, FreeBSD ELF64, execve), rip = 0x254589a5b30a, rsp = 0x2545874dfdf8, rbp = 0x2545874dff40 ---
db> 
db> show proc
Process 37 (sh) at 0xfffffe010e96b000:
 state: NORMAL
 uid: 0  gids: 0
 parent: pid 20 at 0xfffffe003ce595c0
 ABI: FreeBSD ELF64
 flag: 0x14000002  flag2: 0
 arguments: /bin/sh -o verify /etc/rc autoboot
 reaper: 0xfffffe00e4c65040 reapsubtree: 1
 sigparent: 20
 vmspace: 0xfffffe010e95a860
   (map 0xfffffe010e95a860)
   (map.pmap 0xfffffe010e95a920)
   (pmap 0xfffffe010e95a990)
 threads: 1
100210                   Run     CPU 0                       sh
db> 
``

[dougm]

Rewrite the KASSERT at the start of vm_phys_enq_range to handle npages==0.

[pho]

I ran a buildkernel and a few other test with D41154.125493.patch.
I did not observe any issues.