From: Bharata B Rao <bharata@linux.ibm.com>
To: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nathan Lynch <nathanl@linux.ibm.com>,
"Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH v3 0/4] powerpc/mm/radix: Memory unplug fixes
Date: Tue, 21 Jul 2020 08:59:59 +0530 [thread overview]
Message-ID: <20200721032959.GN7902@in.ibm.com> (raw)
In-Reply-To: <87tuy1sksv.fsf@mpe.ellerman.id.au>
On Tue, Jul 21, 2020 at 11:45:20AM +1000, Michael Ellerman wrote:
> Nathan Lynch <nathanl@linux.ibm.com> writes:
> > "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com> writes:
> >> This is the next version of the fixes for memory unplug on radix.
> >> The issues and the fix are described in the actual patches.
> >
> > I guess this isn't actually causing problems at runtime right now, but I
> > notice calls to resize_hpt_for_hotplug() from arch_add_memory() and
> > arch_remove_memory(), which ought to be mmu-agnostic:
> >
> > int __ref arch_add_memory(int nid, u64 start, u64 size,
> > struct mhp_params *params)
> > {
> > unsigned long start_pfn = start >> PAGE_SHIFT;
> > unsigned long nr_pages = size >> PAGE_SHIFT;
> > int rc;
> >
> > resize_hpt_for_hotplug(memblock_phys_mem_size());
> >
> > start = (unsigned long)__va(start);
> > rc = create_section_mapping(start, start + size, nid,
> > params->pgprot);
> > ...
>
> Hmm well spotted.
>
> That does return early if the ops are not setup:
>
> int resize_hpt_for_hotplug(unsigned long new_mem_size)
> {
> unsigned target_hpt_shift;
>
> if (!mmu_hash_ops.resize_hpt)
> return 0;
>
>
> And:
>
> void __init hpte_init_pseries(void)
> {
> ...
> if (firmware_has_feature(FW_FEATURE_HPT_RESIZE))
> mmu_hash_ops.resize_hpt = pseries_lpar_resize_hpt;
>
> And that comes in via ibm,hypertas-functions:
>
> {FW_FEATURE_HPT_RESIZE, "hcall-hpt-resize"},
>
>
> But firmware is not necessarily going to add/remove that call based on
> whether we're using hash/radix.
Correct but hpte_init_pseries() will not be called for radix guests.
>
> So I think a follow-up patch is needed to make this more robust.
>
> Aneesh/Bharata what platform did you test this series on? I'm curious
> how this didn't break.
I have tested memory hotplug/unplug for radix guest on zz platform and
sanity-tested this for hash guest on P8.
As noted above, mmu_hash_ops.resize_hpt will not be set for radix
guest and hence we won't see any breakage.
However a separate patch to fix this will be good.
Regards,
Bharata.
next prev parent reply other threads:[~2020-07-21 3:32 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-09 13:19 [PATCH v3 0/4] powerpc/mm/radix: Memory unplug fixes Aneesh Kumar K.V
2020-07-09 13:19 ` [PATCH v3 1/4] powerpc/mm/radix: Fix PTE/PMD fragment count for early page table mappings Aneesh Kumar K.V
2020-07-09 13:19 ` [PATCH v3 2/4] powerpc/mm/radix: Free PUD table when freeing pagetable Aneesh Kumar K.V
2020-07-09 13:19 ` [PATCH v3 3/4] powerpc/mm/radix: Remove split_kernel_mapping() Aneesh Kumar K.V
2020-07-09 13:19 ` [PATCH v3 4/4] powerpc/mm/radix: Create separate mappings for hot-plugged memory Aneesh Kumar K.V
2020-07-16 14:00 ` [PATCH v3 0/4] powerpc/mm/radix: Memory unplug fixes Nathan Lynch
2020-07-21 1:45 ` Michael Ellerman
2020-07-21 3:29 ` Bharata B Rao [this message]
2020-07-21 12:25 ` Michael Ellerman
2020-07-22 6:05 ` Bharata B Rao
2020-07-22 7:51 ` David Gibson
2020-07-24 11:52 ` Michael Ellerman
2020-07-24 12:17 ` Bharata B Rao
2020-07-25 7:37 ` David Gibson
2020-07-21 4:42 ` Aneesh Kumar K.V
2020-07-24 13:24 ` Michael Ellerman
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