On 17/06/2024 10:40, Barry Song wrote: > On Mon, Jun 17, 2024 at 8:03 PM Ryan Roberts <ryan.roberts@xxxxxxx> wrote: >> >> On 16/06/2024 11:23, Barry Song wrote: >>> On Sun, Jun 16, 2024 at 4:54 PM Christoph Hellwig <hch@xxxxxx> wrote: >>>> >>>> On Sun, Jun 16, 2024 at 12:16:10PM +1200, Barry Song wrote: >>>>> As I understand it, this isn't happening because we don't support >>>>> mTHP swapping out to a swapfile, whether it's on NFS or any >>>>> other filesystem. >>>> >>>> It does happen. The reason why I sent this patch is becaue I observed >>>> the BUG_ON trigger on a trivial swap generation workload (usemem.c from >>>> xfstests). >>> >>> This is quite unusual. Could you share your setup and backtrace? I'd >>> like to reproduce the issue, as the mm code only supports mTHP >>> swapout on block devices. What is your swap device or swap file? >>> Additionally, on what kind of filesystem is the executable file built >>> from usemem.c located? >> >> Yes, I'm also confused by this, since as Barry says, the swap-out changes to >> support mTHP are only intended to be activated when the swap device is a >> non-rotating block device - swap files on file systems are explicitly not >> supported and all swapping should be done page-by-page in that case. This >> constraint is exactly the same as for the pre-existing PMD-size THP swap-out >> support. So if you are seeing large folios being written after the mTHP swap-out >> change, you should also be seeing large folios before this change. >> >> Hopefully the stack trace will tell us what's going on here. > > Hi Ryan, Christoph, > > I am able to reproduce the issue now. I am debugging and will update > the root cause > with you this week. Ahh great; for some reason I'm not receiving Chrostoph's mails so didn't see the stack trace and instructions until you replied to it. I had a go are repro'ing too but am failing to even get the systemd nfs service to start. I'll leave it to you. > > Initial investigation shows the issue might *not* be related to THP_SWPOUT. > > I am even able to reproduce it after disabling thp and mthp, entirely by > small folios: > > [ 215.925069] folio_alloc_swap folio nr:1 anon:1 swapbacked:1 > [ 215.926383] vmscan: shrink_folio_list folio nr:1 anon:1 swapbacked:1 > [ 215.927008] folio_alloc_swap folio nr:1 anon:1 swapbacked:1 > [ 215.929368] ------------[ cut here ]------------ > [ 215.929824] kernel BUG at fs/nfs/direct.c:144! > [ 215.930403] Internal error: Oops - BUG: 00000000f2000800 [#1] PREEMPT SMP > [ 215.931264] Modules linked in: > [ 215.932328] CPU: 3 PID: 214 Comm: mthp_swpout_tes Not tainted > 6.10.0-rc3-ga12328d9fb85-dirty #292 > [ 215.932953] Hardware name: linux,dummy-virt (DT) > [ 215.933461] pstate: 21400005 (nzCv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--) > [ 215.934030] pc : nfs_swap_rw+0x60/0x70 > [ 215.935079] lr : swap_write_unplug+0x64/0xb0 > [ 215.935559] sp : ffff800087363280 > [ 215.935958] x29: ffff800087363280 x28: ffff0000c3241800 x27: fffffdffc323a4c0 > [ 215.937012] x26: fffffdffc323a4c8 x25: ffff0001b4a51500 x24: ffff80008250f670 > [ 215.937893] x23: 0000000000000001 x22: ffff0000c0b2da00 x21: 0000000000020000 > [ 215.938734] x20: ffff0000c46a8bd8 x19: ffff0000c154f800 x18: ffffffffffffffff > [ 215.939594] x17: 0000000000000000 x16: 0000000000000000 x15: ffff800107363097 > [ 215.940591] x14: 0000000000000000 x13: 313a64656b636162 x12: 7061777320313a6e > [ 215.941621] x11: 6f6e6120313a726e x10: ffff800083e86318 x9 : ffff8000803e9ad4 > [ 215.942673] x8 : ffff800087363168 x7 : 0000000000000000 x6 : ffff0001adbfa4c6 > [ 215.943674] x5 : 0000000000000002 x4 : 0000000000020000 x3 : 0000000000020000 > [ 215.944673] x2 : ffff8000806015e8 x1 : ffff8000873632a0 x0 : ffff0000c154f800 > [ 215.945568] Call trace: > [ 215.945906] nfs_swap_rw+0x60/0x70 > [ 215.946351] __swap_writepage+0x2e8/0x328 > [ 215.946775] swap_writepage+0x68/0xd0 > [ 215.947184] pageout+0xe4/0x430 > [ 215.947587] shrink_folio_list+0x9bc/0xf60 > [ 215.947992] reclaim_folio_list+0x8c/0x168 > [ 215.948454] reclaim_pages+0xfc/0x178 > [ 215.948843] madvise_cold_or_pageout_pte_range+0x8d8/0xf28 > [ 215.949285] walk_pgd_range+0x390/0x808 > [ 215.949660] __walk_page_range+0x1e0/0x1f0 > [ 215.950040] walk_page_range+0x1f0/0x2c8 > [ 215.950458] madvise_pageout+0xf8/0x280 > [ 215.950905] madvise_vma_behavior+0x314/0xa20 > [ 215.951361] madvise_walk_vmas+0xc0/0x128 > [ 215.951807] do_madvise.part.0+0x110/0x558 > [ 215.952298] __arm64_sys_madvise+0x68/0x88 > [ 215.952723] invoke_syscall+0x50/0x128 > [ 215.953148] el0_svc_common.constprop.0+0x48/0xf8 > [ 215.953592] do_el0_svc+0x28/0x40 > [ 215.954036] el0_svc+0x50/0x150 > [ 215.954610] el0t_64_sync_handler+0x13c/0x158 > [ 215.955070] el0t_64_sync+0x1a4/0x1a8 > [ 215.955685] Code: a8c17bfd d50323bf 9a9fd000 d65f03c0 (d4210000) > [ 215.956510] ---[ end trace 0000000000000000 ]--- > > >> >> (Sorry for my slow responses/lack of engagement over the last month; its been a >> combination of paternity leave/lack of sleep/working on other things. I'm hoping >> to get properly back into this stuff within the next couple of weeks). >> >> Thanks, >> Ryan >>
