From: David Gibson <david@gibson.dropbear.id.au>
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, bharata@linux.ibm.com
Subject: Re: [PATCH v3 0/4] powerpc/mm/radix: Memory unplug fixes
Date: Sat, 25 Jul 2020 17:37:13 +1000 [thread overview]
Message-ID: <20200725073713.GB84173@umbus.fritz.box> (raw)
In-Reply-To: <87mu3pp1u9.fsf@mpe.ellerman.id.au>
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On Fri, Jul 24, 2020 at 09:52:14PM +1000, Michael Ellerman wrote:
> Bharata B Rao <bharata@linux.ibm.com> writes:
> > On Tue, Jul 21, 2020 at 10:25:58PM +1000, Michael Ellerman wrote:
> >> Bharata B Rao <bharata@linux.ibm.com> writes:
> >> > 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.
> >>
> >> Yeah, duh. You'd think the function name would have been a sufficient
> >> clue for me :)
> >>
> >> >> 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.
> >>
> >> OK.
> >>
> >> That's probably fine as it is then. Or maybe just a comment in
> >> resize_hpt_for_hotplug() pointing out that resize_hpt will be NULL if
> >> we're using radix.
> >
> > Or we could move these calls to hpt-only routines like below?
>
> That looks like it would be equivalent, and would nicely isolate those
> calls in hash specific code. So yeah I think that's worth sending as a
> proper patch, even better if you can test it.
>
> > David - Do you remember if there was any particular reason to have
> > these two hpt-resize calls within powerpc-generic memory hotplug code?
>
> I think the HPT resizing was developed before or concurrently with the
> radix support, so I would guess it was just not something we thought
> about at the time.
Sounds about right; I don't remember for certain.
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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next prev parent reply other threads:[~2020-07-25 7:39 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
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 [this message]
2020-07-21 4:42 ` Aneesh Kumar K.V
2020-07-24 13:24 ` Michael Ellerman
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