Re: [PATCH v6 00/23] migration: File based migration with multifd and mapped-ram

[Peter Xu]

Fabiano,

On Thu, Feb 29, 2024 at 12:29:54PM -0300, Fabiano Rosas wrote:
> => guest: 128 GB RAM - 120 GB dirty - 1 vcpu in tight loop dirtying memory

I'm curious normally how much time does it take to do the final fdatasync()
for you when you did this test.

I finally got a relatively large system today and gave it a quick shot over
128G (100G busy dirty) mapped-ram snapshot with 8 multifd channels.  The
migration save/load does all fine, so I don't think there's anything wrong
with the patchset, however when save completes (I'll need to stop the
workload as my disk isn't fast enough I guess..) I'll always hit a super
long hang of QEMU on fdatasync() on XFS during which the main thread is in
UNINTERRUPTIBLE state.

[<0>] rq_qos_wait+0xbb/0x130
[<0>] wbt_wait+0x9c/0x100
[<0>] __rq_qos_throttle+0x23/0x40
[<0>] blk_mq_submit_bio+0x183/0x580
[<0>] __submit_bio_noacct+0x7e/0x1e0
[<0>] iomap_submit_ioend+0x4e/0x80
[<0>] iomap_writepage_map+0x22a/0x400
[<0>] write_cache_pages+0x17c/0x4c0
[<0>] iomap_writepages+0x1c/0x40
[<0>] xfs_vm_writepages+0x7a/0xb0 [xfs]
[<0>] do_writepages+0xcf/0x1d0
[<0>] filemap_fdatawrite_wbc+0x66/0x90
[<0>] __filemap_fdatawrite_range+0x54/0x80
[<0>] file_write_and_wait_range+0x48/0xb0
[<0>] xfs_file_fsync+0x5a/0x240 [xfs]
[<0>] __x64_sys_fdatasync+0x46/0x80
[<0>] do_syscall_64+0x5c/0x90
[<0>] entry_SYSCALL_64_after_hwframe+0x72/0xdc

Do you also have it, or it's just my host kernel / other config that is
different?

-- 
Peter Xu