So, I forward this to memory management maintainers.
What do you think? - We have a problem that if dm-crypt allocates pages with order > 3 (PAGE_ALLOC_COSTLY_ORDER), the system occasionally freezes waiting in writeback.
dm-crypt allocates the pages with GFP_NOWAIT | __GFP_HIGHMEM | __GFP_NOMEMALLOC | __GFP_NORETRY | __GFP_NOWARN | __GFP_COMP, so it shouldn't put any pressure on the system. If the allocations fails, it falls back to smaller order allocation or to mempool as a last resort.
When the freeze happens, there is "349264kB" free memory - so the system is not short on memory.
Should we restrict the dm-crypt allocation size to PAGE_ALLOC_COSTLY_ORDER? Or is it a bug somewhere in memory management system that needs to be fixes there?
Mikulas
On Wed, 25 Oct 2023, Marek Marczykowski-Górecki wrote:
On Wed, Oct 25, 2023 at 05:10:56AM +0200, Marek Marczykowski-Górecki wrote:
On Mon, Oct 23, 2023 at 10:59:40PM +0200, Mikulas Patocka wrote:
Hi
It's hard to say what causes this. Perhaps dm-crypt exhausts all the higher-order pages and some subsystem stalls because of it.
In drivers/md/dm-crypt.c in function crypt_alloc_buffer there is "unsigned int order = MAX_ORDER - 1"
What happens if you set the "order" variable to some small value, like 1, 2 or 3. Does the problem go away? Could you find a threshold value (something between 0 and MAX_ORDER-1) where the bug starts to appear?
With 3 and lower it seems to work, with 4 it freezes. My test is not 100% reproducible, but I've repeated it a few times and got rather consistent results on this system (i3-1315U, NVMe).
BTW, when trying on a much older system (Thinkpad P52 with i7-8750H) I couldn't reproduce the issue at all. But OTOH, I hit it once on a system with i7-7600U and otherwise similar specs but much different workload (several more VMs accessing the data). I'm not sure if that info helps at all...
What happens if you replace "pages = alloc_pages(gfp_mask" with "pages = alloc_pages((gfp_mask & ~__GFP_KSWAPD_RECLAIM)" ? Does the bug go away?
In a limited test, with order restored to MAX_ORDER - 1, no, still got the issue, and got this via sysrq (just one task listed):
[ 516.375254] sysrq: Show Blocked State [ 516.375461] task:dd state:D stack:13072 pid:4385 ppid:4371 flags:0x00004002 [ 516.375496] Call Trace: [ 516.375507] <TASK> [ 516.375518] __schedule+0x30e/0x8b0 [ 516.375549] schedule+0x59/0xb0 [ 516.375566] io_schedule+0x41/0x70 [ 516.375582] folio_wait_bit_common+0x12c/0x300 [ 516.375603] ? __pfx_wake_page_function+0x10/0x10 [ 516.375623] folio_wait_writeback+0x27/0x80 [ 516.375639] __filemap_fdatawait_range+0x7b/0xe0 [ 516.375656] file_write_and_wait_range+0x86/0xb0 [ 516.375672] blkdev_fsync+0x33/0x60 [ 516.375693] __x64_sys_fdatasync+0x4a/0x90 [ 516.375713] do_syscall_64+0x3c/0x90 [ 516.375729] entry_SYSCALL_64_after_hwframe+0x6e/0xd8 [ 516.375751] RIP: 0033:0x7fd718562da4 [ 516.375764] RSP: 002b:00007ffea3815278 EFLAGS: 00000202 ORIG_RAX: 000000000000004b [ 516.375784] RAX: ffffffffffffffda RBX: 0000000000015200 RCX: 00007fd718562da4 [ 516.375801] RDX: 0000000000028000 RSI: 0000000000000000 RDI: 0000000000000001 [ 516.375817] RBP: 00007fd71845e6c0 R08: 00000000ffffffff R09: 0000000000000000 [ 516.375833] R10: 0000000000000022 R11: 0000000000000202 R12: 0000000000000000 [ 516.375848] R13: 0000000000000000 R14: 0000000000028000 R15: 0000000000000000 [ 516.375865] </TASK>
(it is dd writing to LVM thin volume, where PV is on dm-crypt)
In this bad state, I extracted some more info on memory:
/proc/meminfo:
MemTotal: 3983088 kB MemFree: 349264 kB MemAvailable: 3474744 kB Buffers: 1511732 kB Cached: 1608132 kB SwapCached: 12 kB Active: 203136 kB Inactive: 3147696 kB Active(anon): 1288 kB Inactive(anon): 252128 kB Active(file): 201848 kB Inactive(file): 2895568 kB Unevictable: 46064 kB Mlocked: 39920 kB SwapTotal: 4112380 kB SwapFree: 4112124 kB Dirty: 0 kB Writeback: 8556 kB AnonPages: 277020 kB Mapped: 137424 kB Shmem: 13792 kB KReclaimable: 91728 kB Slab: 182428 kB SReclaimable: 91728 kB SUnreclaim: 90700 kB KernelStack: 5776 kB PageTables: 7480 kB SecPageTables: 0 kB NFS_Unstable: 0 kB Bounce: 0 kB WritebackTmp: 0 kB CommitLimit: 6103924 kB Committed_AS: 990924 kB VmallocTotal: 34359738367 kB VmallocUsed: 11560 kB VmallocChunk: 0 kB Percpu: 2528 kB DirectMap4k: 4325764 kB DirectMap2M: 0 kB
and also: [ 1168.537096] sysrq: Show Memory [ 1168.537192] Mem-Info: [ 1168.537206] active_anon:322 inactive_anon:63032 isolated_anon:0 [ 1168.537206] active_file:50462 inactive_file:723892 isolated_file:0 [ 1168.537206] unevictable:11516 dirty:1 writeback:2139 [ 1168.537206] slab_reclaimable:22932 slab_unreclaimable:22675 [ 1168.537206] mapped:34357 shmem:3448 pagetables:1870 [ 1168.537206] sec_pagetables:0 bounce:0 [ 1168.537206] kernel_misc_reclaimable:0 [ 1168.537206] free:87499 free_pcp:1642 free_cma:0 [ 1168.537279] Node 0 active_anon:1288kB inactive_anon:252128kB active_file:201848kB inactive_file:2895568kB unevictable:46064kB isolated(anon):0kB isolated(file):0kB mapped:137428kB dirty:4kB writeback:8556kB shmem:13792kB writeback_tmp:0kB kernel_stack:5776kB pagetables:7480kB sec_pagetables:0kB all_unreclaimable? no [ 1168.537332] Node 0 DMA free:15488kB boost:0kB min:32kB low:44kB high:56kB reserved_highatomic:0KB active_anon:0kB inactive_anon:0kB active_file:84kB inactive_file:352kB unevictable:0kB writepending:84kB present:15996kB managed:15936kB mlocked:0kB bounce:0kB free_pcp:12kB local_pcp:0kB free_cma:0kB [ 1168.537387] lowmem_reserve[]: 0 1728 3857 3857 [ 1168.537409] Node 0 DMA32 free:155300kB boost:0kB min:3552kB low:5320kB high:7088kB reserved_highatomic:0KB active_anon:16kB inactive_anon:3368kB active_file:5660kB inactive_file:1585120kB unevictable:0kB writepending:7576kB present:1924360kB managed:1803376kB mlocked:0kB bounce:0kB free_pcp:3184kB local_pcp:864kB free_cma:0kB [ 1168.537464] lowmem_reserve[]: 0 0 2129 2129 [ 1168.537483] Node 0 Normal free:179208kB boost:0kB min:4376kB low:6556kB high:8736kB reserved_highatomic:2048KB active_anon:1272kB inactive_anon:248760kB active_file:196104kB inactive_file:1310096kB unevictable:46064kB writepending:900kB present:2253948kB managed:2163776kB mlocked:39920kB bounce:0kB free_pcp:3372kB local_pcp:632kB free_cma:0kB [ 1168.537540] lowmem_reserve[]: 0 0 0 0 [ 1168.537557] Node 0 DMA: 4*4kB (UM) 4*8kB (UM) 3*16kB (UM) 3*32kB (U) 3*64kB (U) 2*128kB (UM) 0*256kB 1*512kB (M) 2*1024kB (UM) 0*2048kB 3*4096kB (M) = 15488kB [ 1168.537624] Node 0 DMA32: 1945*4kB (UME) 1446*8kB (UME) 953*16kB (UME) 1410*32kB (UM) 297*64kB (UM) 162*128kB (UM) 60*256kB (UM) 22*512kB (UM) 7*1024kB (UM) 1*2048kB (U) 0*4096kB = 155300kB [ 1168.537695] Node 0 Normal: 3146*4kB (UMEH) 2412*8kB (UMEH) 1444*16kB (UMEH) 1138*32kB (UMEH) 486*64kB (UME) 97*128kB (UM) 13*256kB (UM) 8*512kB (M) 2*1024kB (M) 5*2048kB (M) 6*4096kB (UM) = 179208kB [ 1168.537767] 779973 total pagecache pages [ 1168.537778] 3 pages in swap cache [ 1168.537788] Free swap = 4112124kB [ 1168.537798] Total swap = 4112380kB [ 1168.537807] 1048576 pages RAM [ 1168.537817] 0 pages HighMem/MovableOnly [ 1168.537827] 52804 pages reserved
Mikulas
On Sat, 21 Oct 2023, Marek Marczykowski-Górecki wrote:
Hi,
Since updating from 6.4.13 to 6.5.5 occasionally I hit a storage subsystem freeze - any I/O ends up frozen. I'm not sure what exactly triggers the issue, but often it happens when doing some LVM operations (lvremove, lvrename etc) on a dm-thin volume together with bulk data copy to/from another LVM thin volume with ext4 fs.
The storage stack I use is: nvme -> dm-crypt (LUKS) -> dm-thin (LVM thin pool) -> ext4
And this whole thing running in a (PV) dom0 under Xen, on Qubes OS 4.2 to be specific.
I can reproduce the issue on at least 3 different machines. I did tried also 6.5.6 and the issue is still there. I haven't checked newer versions, but briefly reviewed git log and haven't found anything suggesting a fix to similar issue.
I managed to bisect it down to this commit:
commit 5054e778fcd9cd29ddaa8109077cd235527e4f94 Author: Mikulas Patocka <mpatocka@redhat.com> Date: Mon May 1 09:19:17 2023 -0400 dm crypt: allocate compound pages if possibleIt was reported that allocating pages for the write buffer in dm-crypt causes measurable overhead [1]. Change dm-crypt to allocate compound pages if they are available. If not, fall back to the mempool. [1] https://listman.redhat.com/archives/dm-devel/2023-February/053284.html Suggested-by: Matthew Wilcox willy@infradead.org Signed-off-by: Mikulas Patocka mpatocka@redhat.com Signed-off-by: Mike Snitzer snitzer@kernel.org
TBH, I'm not sure if the bug is in this commit, or maybe in some functions it uses (I don't see dm-crypt functions directly involved in the stack traces I collected). But reverting this commit on top of 6.5.6 seems to fix the issue.
I tried also CONFIG_PROVE_LOCKING, but it didn't show any issue.
I managed to collect "blocked tasks" dump via sysrq below. Few more can be found at https://github.com/QubesOS/qubes-issues/issues/8575
[ 4246.558313] sysrq: Show Blocked State [ 4246.558388] task:journal-offline state:D stack:0 pid:8098 ppid:1 flags:0x00000002 [ 4246.558407] Call Trace: [ 4246.558414] <TASK> [ 4246.558422] __schedule+0x23d/0x670 [ 4246.558440] schedule+0x5e/0xd0 [ 4246.558450] io_schedule+0x46/0x70 [ 4246.558461] folio_wait_bit_common+0x13d/0x350 [ 4246.558475] ? __pfx_wake_page_function+0x10/0x10 [ 4246.558488] folio_wait_writeback+0x2c/0x90 [ 4246.558498] mpage_prepare_extent_to_map+0x15c/0x4d0 [ 4246.558512] ext4_do_writepages+0x25f/0x770 [ 4246.558523] ext4_writepages+0xad/0x180 [ 4246.558533] do_writepages+0xcf/0x1e0 [ 4246.558543] ? __seccomp_filter+0x32a/0x4f0 [ 4246.558554] filemap_fdatawrite_wbc+0x63/0x90 [ 4246.558567] __filemap_fdatawrite_range+0x5c/0x80 [ 4246.558578] file_write_and_wait_range+0x4a/0xb0 [ 4246.558588] ext4_sync_file+0x88/0x380 [ 4246.558598] __x64_sys_fsync+0x3b/0x70 [ 4246.558609] do_syscall_64+0x5c/0x90 [ 4246.558621] ? exit_to_user_mode_prepare+0xb2/0xd0 [ 4246.558632] entry_SYSCALL_64_after_hwframe+0x6e/0xd8 [ 4246.558644] RIP: 0033:0x7710cf124d0a [ 4246.558654] RSP: 002b:00007710ccdfda40 EFLAGS: 00000293 ORIG_RAX: 000000000000004a [ 4246.558668] RAX: ffffffffffffffda RBX: 000064bb92f67e60 RCX: 00007710cf124d0a [ 4246.558679] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000028 [ 4246.558691] RBP: 000064bb92f72670 R08: 0000000000000000 R09: 00007710ccdfe6c0 [ 4246.558702] R10: 00007710cf0adfee R11: 0000000000000293 R12: 000064bb92505940 [ 4246.558713] R13: 0000000000000002 R14: 00007ffc05649500 R15: 00007710cc5fe000 [ 4246.558728] </TASK> [ 4246.558836] task:lvm state:D stack:0 pid:7835 ppid:5665 flags:0x00004006 [ 4246.558852] Call Trace: [ 4246.558857] <TASK> [ 4246.558863] __schedule+0x23d/0x670 [ 4246.558874] schedule+0x5e/0xd0 [ 4246.558884] io_schedule+0x46/0x70 [ 4246.558894] dm_wait_for_bios_completion+0xfc/0x110 [ 4246.558909] ? __pfx_autoremove_wake_function+0x10/0x10 [ 4246.558922] __dm_suspend+0x7e/0x1b0 [ 4246.558932] dm_internal_suspend_noflush+0x5c/0x80 [ 4246.558946] pool_presuspend+0xcc/0x130 [dm_thin_pool] [ 4246.558968] dm_table_presuspend_targets+0x3f/0x60 [ 4246.558980] __dm_suspend+0x41/0x1b0 [ 4246.558991] dm_suspend+0xc0/0xe0 [ 4246.559001] dev_suspend+0xa5/0xd0 [ 4246.559011] ctl_ioctl+0x26e/0x350 [ 4246.559020] ? __pfx_dev_suspend+0x10/0x10 [ 4246.559032] dm_ctl_ioctl+0xe/0x20 [ 4246.559041] __x64_sys_ioctl+0x94/0xd0 [ 4246.559052] do_syscall_64+0x5c/0x90 [ 4246.559062] ? do_syscall_64+0x6b/0x90 [ 4246.559072] ? do_syscall_64+0x6b/0x90 [ 4246.559081] ? xen_pv_evtchn_do_upcall+0x54/0xb0 [ 4246.559093] entry_SYSCALL_64_after_hwframe+0x6e/0xd8 [ 4246.559104] RIP: 0033:0x7f1cb77cfe0f [ 4246.559112] RSP: 002b:00007fff870f2560 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 [ 4246.559141] RAX: ffffffffffffffda RBX: 00005b8d13c16580 RCX: 00007f1cb77cfe0f [ 4246.559152] RDX: 00005b8d144a2180 RSI: 00000000c138fd06 RDI: 0000000000000003 [ 4246.559164] RBP: 00005b8d144a2180 R08: 00005b8d132b1190 R09: 00007fff870f2420 [ 4246.559175] R10: 0000000000000000 R11: 0000000000000246 R12: 000000000000000c [ 4246.559186] R13: 00005b8d132aacf0 R14: 00005b8d1324414d R15: 00005b8d144a21b0 [ 4246.559199] </TASK> [ 4246.559207] task:kworker/u8:3 state:D stack:0 pid:8033 ppid:2 flags:0x00004000 [ 4246.559222] Workqueue: writeback wb_workfn (flush-253:4) [ 4246.559238] Call Trace: [ 4246.559244] <TASK> [ 4246.559249] __schedule+0x23d/0x670 [ 4246.559260] schedule+0x5e/0xd0 [ 4246.559270] io_schedule+0x46/0x70 [ 4246.559280] folio_wait_bit_common+0x13d/0x350 [ 4246.559290] ? __pfx_wake_page_function+0x10/0x10 [ 4246.559302] mpage_prepare_extent_to_map+0x309/0x4d0 [ 4246.559314] ext4_do_writepages+0x25f/0x770 [ 4246.559324] ext4_writepages+0xad/0x180 [ 4246.559334] do_writepages+0xcf/0x1e0 [ 4246.559344] ? find_busiest_group+0x42/0x1a0 [ 4246.559354] __writeback_single_inode+0x3d/0x280 [ 4246.559368] writeback_sb_inodes+0x1ed/0x4a0 [ 4246.559381] __writeback_inodes_wb+0x4c/0xf0 [ 4246.559393] wb_writeback+0x298/0x310 [ 4246.559403] wb_do_writeback+0x230/0x2b0 [ 4246.559414] wb_workfn+0x5f/0x260 [ 4246.559424] ? _raw_spin_unlock+0xe/0x30 [ 4246.559434] ? finish_task_switch.isra.0+0x95/0x2b0 [ 4246.559447] ? __schedule+0x245/0x670 [ 4246.559457] process_one_work+0x1df/0x3e0 [ 4246.559466] worker_thread+0x51/0x390 [ 4246.559475] ? __pfx_worker_thread+0x10/0x10 [ 4246.559484] kthread+0xe5/0x120 [ 4246.559495] ? __pfx_kthread+0x10/0x10 [ 4246.559504] ret_from_fork+0x31/0x50 [ 4246.559514] ? __pfx_kthread+0x10/0x10 [ 4246.559523] ret_from_fork_asm+0x1b/0x30 [ 4246.559536] </TASK>-- Best Regards, Marek Marczykowski-Górecki Invisible Things Lab
-- Best Regards, Marek Marczykowski-Górecki Invisible Things Lab
-- Best Regards, Marek Marczykowski-Górecki Invisible Things Lab