Re: [PATCH v5 3/3] mm: don't account memmap per-node

[Yi Zhang]

Thanks for the fix.
Tested-by: Yi Zhang <yi.zhang@xxxxxxxxxx>

On Mon, Aug 12, 2024 at 4:26 AM David Rientjes <rientjes@xxxxxxxxxx> wrote:
>
> On Fri, 9 Aug 2024, Pasha Tatashin wrote:
>
> > Fix invalid access to pgdat during hot-remove operation:
> > ndctl users reported a GPF when trying to destroy a namespace:
> > $ ndctl destroy-namespace all -r all -f
> >  Segmentation fault
> >  dmesg:
> >  Oops: general protection fault, probably for
> >  non-canonical address 0xdffffc0000005650: 0000 [#1] PREEMPT SMP KASAN
> >  PTI
> >  KASAN: probably user-memory-access in range
> >  [0x000000000002b280-0x000000000002b287]
> >  CPU: 26 UID: 0 PID: 1868 Comm: ndctl Not tainted 6.11.0-rc1 #1
> >  Hardware name: Dell Inc. PowerEdge R640/08HT8T, BIOS
> >  2.20.1 09/13/2023
> >  RIP: 0010:mod_node_page_state+0x2a/0x110
> >
> > cxl-test users report a GPF when trying to unload the test module:
> > $ modrpobe -r cxl-test
> >  dmesg
> >  BUG: unable to handle page fault for address: 0000000000004200
> >  #PF: supervisor read access in kernel mode
> >  #PF: error_code(0x0000) - not-present page
> >  PGD 0 P4D 0
> >  Oops: Oops: 0000 [#1] PREEMPT SMP PTI
> >  CPU: 0 UID: 0 PID: 1076 Comm: modprobe Tainted: G O N 6.11.0-rc1 #197
> >  Tainted: [O]=OOT_MODULE, [N]=TEST
> >  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/15
> >  RIP: 0010:mod_node_page_state+0x6/0x90
> >
> > Currently, when memory is hot-plugged or hot-removed the accounting is
> > done based on the assumption that memmap is allocated from the same node
> > as the hot-plugged/hot-removed memory, which is not always the case.
> >
> > In addition, there are challenges with keeping the node id of the memory
> > that is being remove to the time when memmap accounting is actually
> > performed: since this is done after remove_pfn_range_from_zone(), and
> > also after remove_memory_block_devices(). Meaning that we cannot use
> > pgdat nor walking though memblocks to get the nid.
> >
> > Given all of that, account the memmap overhead system wide instead.
> >
> > For this we are going to be using global atomic counters, but given that
> > memmap size is rarely modified, and normally is only modified either
> > during early boot when there is only one CPU, or under a hotplug global
> > mutex lock, therefore there is no need for per-cpu optimizations.
> >
> > Also, while we are here rename nr_memmap to nr_memmap_pages, and
> > nr_memmap_boot to nr_memmap_boot_pages to be self explanatory that the
> > units are in page count.
> >
> > Reported-by: Yi Zhang <yi.zhang@xxxxxxxxxx>
> > Closes: https://lore.kernel.org/linux-cxl/CAHj4cs9Ax1=CoJkgBGP_+sNu6-6=6v=_L-ZBZY0bVLD3wUWZQg@xxxxxxxxxxxxxx
> > Reported-by: Alison Schofield <alison.schofield@xxxxxxxxx>
> > Closes: https://lore.kernel.org/linux-mm/Zq0tPd2h6alFz8XF@aschofie-mobl2/#t
> >
> > Fixes: 15995a352474 ("mm: report per-page metadata information")
> > Signed-off-by: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx>
> > Tested-by: Dan Williams <dan.j.williams@xxxxxxxxx>
> > Tested-by: Alison Schofield <alison.schofield@xxxxxxxxx>
> > Acked-by: David Hildenbrand <david@xxxxxxxxxx>
>
> Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
>


-- 
Best Regards,
  Yi Zhang