lkml.org 
[lkml]   [2018]   [Oct]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    Date
    SubjectRe: [PATCH v5 4/4] mm: Defer ZONE_DEVICE page initialization to the point where we init pgmap
    On Mon, Oct 8, 2018 at 2:48 PM Alexander Duyck
    <alexander.h.duyck@linux.intel.com> wrote:
    >
    > On 10/8/2018 2:01 PM, Dan Williams wrote:
    > > On Tue, Sep 25, 2018 at 1:29 PM Alexander Duyck
    > > <alexander.h.duyck@linux.intel.com> wrote:
    > >>
    > >> The ZONE_DEVICE pages were being initialized in two locations. One was with
    > >> the memory_hotplug lock held and another was outside of that lock. The
    > >> problem with this is that it was nearly doubling the memory initialization
    > >> time. Instead of doing this twice, once while holding a global lock and
    > >> once without, I am opting to defer the initialization to the one outside of
    > >> the lock. This allows us to avoid serializing the overhead for memory init
    > >> and we can instead focus on per-node init times.
    > >>
    > >> One issue I encountered is that devm_memremap_pages and
    > >> hmm_devmmem_pages_create were initializing only the pgmap field the same
    > >> way. One wasn't initializing hmm_data, and the other was initializing it to
    > >> a poison value. Since this is something that is exposed to the driver in
    > >> the case of hmm I am opting for a third option and just initializing
    > >> hmm_data to 0 since this is going to be exposed to unknown third party
    > >> drivers.
    > >>
    > >> Reviewed-by: Pavel Tatashin <pavel.tatashin@microsoft.com>
    > >> Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
    > >> ---
    > >>
    > >> v4: Moved moved memmap_init_zone_device to below memmmap_init_zone to avoid
    > >> merge conflicts with other changes in the kernel.
    > >> v5: No change
    > >
    > > This patch appears to cause a regression in the "create.sh" unit test
    > > in the ndctl test suite.
    >
    > So all you had to do is run the create.sh script to see the issue? I
    > just want to confirm there isn't any additional information needed
    > before I try chasing this down.

    From the ndctl source tree run:

    make -j TESTS="create.sh" check

    ...the readme has some more setup instructions:
    https://github.com/pmem/ndctl/blob/master/README.md

    0day has sometimes run this test suite automatically, but we need to
    get that more robust because setting up this environment is a bit of a
    hoop to jump through with the need to setup the nfit_test module.

    > > I tried to reproduce on -next with:
    > >
    > > 2302f5ee215e mm: defer ZONE_DEVICE page initialization to the point
    > > where we init pgmap
    > >
    > > ...but -next does not even boot for me at that commit.
    >
    > What version of -next? There are a couple of patches probably needed
    > depending on which version you are trying to boot.

    Today's -next, but backed up to that above commit. I was also seeing
    CONFIG_DEBUG_LIST spamming the logs, and a crash in the crypto layer.

    > > Here is a warning signature that proceeds a hang with this patch
    > > applied against v4.19-rc6:
    > >
    > > percpu ref (blk_queue_usage_counter_release) <= 0 (-1530626) after
    > > switching to atomic
    > > WARNING: CPU: 24 PID: 7346 at lib/percpu-refcount.c:155
    > > percpu_ref_switch_to_atomic_rcu+0x1f7/0x200
    > > CPU: 24 PID: 7346 Comm: modprobe Tainted: G OE 4.19.0-rc6+ #2458
    > > [..]
    > > RIP: 0010:percpu_ref_switch_to_atomic_rcu+0x1f7/0x200
    > > [..]
    > > Call Trace:
    > > <IRQ>
    > > ? percpu_ref_reinit+0x140/0x140
    > > rcu_process_callbacks+0x273/0x880
    > > __do_softirq+0xd2/0x428
    > > irq_exit+0xf6/0x100
    > > smp_apic_timer_interrupt+0xa2/0x220
    > > apic_timer_interrupt+0xf/0x20
    > > </IRQ>
    > > RIP: 0010:lock_acquire+0xb8/0x1a0
    > > [..]
    > > ? __put_page+0x55/0x150
    > > ? __put_page+0x55/0x150
    > > __put_page+0x83/0x150
    > > ? __put_page+0x55/0x150
    > > devm_memremap_pages_release+0x194/0x250
    > > release_nodes+0x17c/0x2c0
    > > device_release_driver_internal+0x1a2/0x250
    > > driver_detach+0x3a/0x70
    > > bus_remove_driver+0x58/0xd0
    > > __x64_sys_delete_module+0x13f/0x200
    > > ? trace_hardirqs_off_thunk+0x1a/0x1c
    > > do_syscall_64+0x60/0x210
    > > entry_SYSCALL_64_after_hwframe+0x49/0xbe
    > >
    >
    > So it looks like we are tearing down memory when this is triggered. Do
    > we know if this is at the end of the test or if this is running in
    > parallel with anything?

    Should not be running in parallel with anything this test is
    performing a series of namespace setup and teardown events.

    Wait, where did the call to "percpu_ref_get()" go? I think that's the bug.

    \
     
     \ /
      Last update: 2018-10-09 00:02    [W:4.023 / U:0.712 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site