Alistair Popple wrote: > FS DAX pages have always maintained their own page reference counts > without following the normal rules for page reference counting. In > particular pages are considered free when the refcount hits one rather > than zero and refcounts are not added when mapping the page. > > Tracking this requires special PTE bits (PTE_DEVMAP) and a secondary > mechanism for allowing GUP to hold references on the page (see > get_dev_pagemap). However there doesn't seem to be any reason why FS > DAX pages need their own reference counting scheme. > > By treating the refcounts on these pages the same way as normal pages > we can remove a lot of special checks. In particular pXd_trans_huge() > becomes the same as pXd_leaf(), although I haven't made that change > here. It also frees up a valuable SW define PTE bit on architectures > that have devmap PTE bits defined. > > It also almost certainly allows further clean-up of the devmap managed > functions, but I have left that as a future improvment. > > This is an update to the original RFC rebased onto v6.10-rc5. Unlike > the original RFC it passes the same number of ndctl test suite > (https://github.com/pmem/ndctl) tests as my current development > environment does without these patches. Are you seeing the 'mmap.sh' test fail even without these patches? I see this with the patches, will try without in the morning. EXT4-fs (pmem0): unmounting filesystem 26ea1463-343a-464f-9f16-91cb176dbdc7. XFS (pmem0): Mounting V5 Filesystem 554953fd-c9f4-460f-bc37-f43979986b68 XFS (pmem0): Ending clean mount Oops: general protection fault, probably for non-canonical address 0xdead000000000518: 00 T SMP PTI CPU: 15 PID: 1295 Comm: mmap Tainted: G OE N 6.10.0-rc5+ #261 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS edk2-20240524-3.fc40 05/24/2024 RIP: 0010:folio_mark_dirty+0x25/0x60 Code: 90 90 90 90 90 0f 1f 44 00 00 53 48 89 fb e8 22 18 02 00 48 85 c0 74 26 48 89 c7 48 0 02 00 74 05 f0 80 63 02 fd <48> 8b 87 18 01 00 00 48 89 de 5b 48 8b 40 18 e9 77 90 c0 00 RSP: 0018:ffffb073022f7b08 EFLAGS: 00010246 RAX: 004ffff800002000 RBX: ffffd0d005000300 RCX: 0400000000000040 RDX: 0000000000000000 RSI: 00007f4006200000 RDI: dead000000000400 RBP: 0000000000000000 R08: ffff9a4b04504a30 R09: 000fffffffffffff R10: ffffd0d005000300 R11: 0000000000000000 R12: 00007f4006200000 R13: ffff9a4b7c96c000 R14: ffff9a4b7daba440 R15: ffffb073022f7cb0 FS: 00007f4046351740(0000) GS:ffff9a4d77780000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f40461ff000 CR3: 000000027aea6000 CR4: 00000000000006f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: <TASK> ? __die_body.cold+0x19/0x26 ? die_addr+0x38/0x60 ? exc_general_protection+0x143/0x420 ? asm_exc_general_protection+0x22/0x30 ? folio_mark_dirty+0x25/0x60 ? folio_mark_dirty+0xe/0x60 unmap_page_range+0xea5/0x1550 unmap_vmas+0xf8/0x1e0 unmap_region.constprop.0+0xd7/0x150 ? lock_is_held_type+0xd5/0x130 do_vmi_align_munmap.isra.0+0x3f4/0x580 ? mas_walk+0x101/0x1b0 __vm_munmap+0xa6/0x170 __x64_sys_munmap+0x17/0x20 do_syscall_64+0x75/0x190 entry_SYSCALL_64_after_hwframe+0x76/0x7e $ faddr2line vmlinux folio_mark_dirty+0x25 folio_mark_dirty+0x25/0x58: folio_mark_dirty at mm/page-writeback.c:2860
