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Date:   Thu, 10 Sep 2020 14:03:48 +0200
From:   Oscar Salvador <osalvador@suse.de>
To:     Laurent Dufour <ldufour@linux.ibm.com>
Cc:     Michal Hocko <mhocko@suse.com>, akpm@linux-foundation.org,
        David Hildenbrand <david@redhat.com>, rafael@kernel.org,
        nathanl@linux.ibm.com, cheloha@linux.ibm.com,
        stable@vger.kernel.org,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-mm@kvack.org, LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] mm: don't rely on system state to detect hot-plug
 operations
Message-ID: <20200910120343.GA6635@linux>
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On Thu, Sep 10, 2020 at 01:35:32PM +0200, Laurent Dufour wrote:
 
> That points has been raised by David, quoting him here:
> 
> > IIRC, ACPI can hotadd memory while SCHEDULING, this patch would break that.
> > 
> > Ccing Oscar, I think he mentioned recently that this is the case with ACPI.
> 
> Oscar told that he need to investigate further on that.

I think my reply got lost.

We can see acpi hotplugs during SYSTEM_SCHEDULING:

$QEMU -enable-kvm -machine pc -smp 4,sockets=4,cores=1,threads=1 -cpu host -monitor pty \
        -m size=$MEM,slots=255,maxmem=4294967296k  \
        -numa node,nodeid=0,cpus=0-3,mem=512 -numa node,nodeid=1,mem=512 \
        -object memory-backend-ram,id=memdimm0,size=134217728 -device pc-dimm,node=0,memdev=memdimm0,id=dimm0,slot=0 \
        -object memory-backend-ram,id=memdimm1,size=134217728 -device pc-dimm,node=0,memdev=memdimm1,id=dimm1,slot=1 \
        -object memory-backend-ram,id=memdimm2,size=134217728 -device pc-dimm,node=0,memdev=memdimm2,id=dimm2,slot=2 \
        -object memory-backend-ram,id=memdimm3,size=134217728 -device pc-dimm,node=0,memdev=memdimm3,id=dimm3,slot=3 \
        -object memory-backend-ram,id=memdimm4,size=134217728 -device pc-dimm,node=1,memdev=memdimm4,id=dimm4,slot=4 \
        -object memory-backend-ram,id=memdimm5,size=134217728 -device pc-dimm,node=1,memdev=memdimm5,id=dimm5,slot=5 \
        -object memory-backend-ram,id=memdimm6,size=134217728 -device pc-dimm,node=1,memdev=memdimm6,id=dimm6,slot=6 \

kernel: [    0.753643] __add_memory: nid: 0 start: 0100000000 - 0108000000 (size: 134217728)
kernel: [    0.756950] register_mem_sect_under_node: system_state= 1

kernel: [    0.760811]  register_mem_sect_under_node+0x4f/0x230
kernel: [    0.760811]  walk_memory_blocks+0x80/0xc0
kernel: [    0.760811]  link_mem_sections+0x32/0x40
kernel: [    0.760811]  add_memory_resource+0x148/0x250
kernel: [    0.760811]  __add_memory+0x5b/0x90
kernel: [    0.760811]  acpi_memory_device_add+0x130/0x300
kernel: [    0.760811]  acpi_bus_attach+0x13c/0x1c0
kernel: [    0.760811]  acpi_bus_attach+0x60/0x1c0
kernel: [    0.760811]  acpi_bus_scan+0x33/0x70
kernel: [    0.760811]  acpi_scan_init+0xea/0x21b
kernel: [    0.760811]  acpi_init+0x2f1/0x33c
kernel: [    0.760811]  do_one_initcall+0x46/0x1f4


-- 
Oscar Salvador
SUSE L3