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Tue, 21 Jul 2020 03:30:01 +0000 (GMT) Date: Tue, 21 Jul 2020 08:59:59 +0530 From: Bharata B Rao To: Michael Ellerman Subject: Re: [PATCH v3 0/4] powerpc/mm/radix: Memory unplug fixes Message-ID: <20200721032959.GN7902@in.ibm.com> References: <20200709131925.922266-1-aneesh.kumar@linux.ibm.com> <87r1tb1rw2.fsf@linux.ibm.com> <87tuy1sksv.fsf@mpe.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87tuy1sksv.fsf@mpe.ellerman.id.au> X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.235, 18.0.687 definitions=2020-07-20_09:2020-07-20, 2020-07-20 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 clxscore=1015 phishscore=0 impostorscore=0 mlxscore=0 spamscore=0 lowpriorityscore=0 priorityscore=1501 bulkscore=0 mlxlogscore=999 adultscore=0 suspectscore=1 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2007210016 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: bharata@linux.ibm.com Cc: Nathan Lynch , "Aneesh Kumar K.V" , linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Tue, Jul 21, 2020 at 11:45:20AM +1000, Michael Ellerman wrote: > Nathan Lynch writes: > > "Aneesh Kumar K.V" 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.