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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 21 Jan 2026 08:16:51.0756 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 2bfeabcb-9744-432a-922a-08de58c56e12 X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[4.158.2.129];Helo=[outbound-uk1.az.dlp.m.darktrace.com] X-MS-Exchange-CrossTenant-AuthSource: AM1PEPF000252DA.eurprd07.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: PR3PR08MB5787 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260121_001700_667642_1D2C2C1D X-CRM114-Status: GOOD ( 12.96 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Yang, > > > On 1/20/26 3:01 PM, Yeoreum Yun wrote: > > Hi Yang, > > > > > > On 1/20/26 1:29 AM, Yeoreum Yun wrote: > > > > Hi Ryan > > > > > On 19/01/2026 21:24, Yeoreum Yun wrote: > > > > > > Hi Will, > > > > > > > > > > > > > On Mon, Jan 05, 2026 at 08:23:27PM +0000, Yeoreum Yun wrote: > > > > > > > > +static int __init linear_map_prealloc_split_pgtables(void) > > > > > > > > +{ > > > > > > > > + int ret, i; > > > > > > > > + unsigned long lstart = _PAGE_OFFSET(vabits_actual); > > > > > > > > + unsigned long lend = PAGE_END; > > > > > > > > + unsigned long kstart = (unsigned long)lm_alias(_stext); > > > > > > > > + unsigned long kend = (unsigned long)lm_alias(__init_begin); > > > > > > > > + > > > > > > > > + const struct mm_walk_ops collect_to_split_ops = { > > > > > > > > + .pud_entry = collect_to_split_pud_entry, > > > > > > > > + .pmd_entry = collect_to_split_pmd_entry > > > > > > > > + }; > > > > > > > Why do we need to rewalk the page-table here instead of collating the > > > > > > > number of block mappings we put down when creating the linear map in > > > > > > > the first place? > > > > > That's a good point; perhaps we can reuse the counters that this series introduces? > > > > > > > > > > https://lore.kernel.org/all/20260107002944.2940963-1-yang@os.amperecomputing.com/ > > > Yeah, good point. It seems feasible to me. The patch can count how many > > > PUD/CONT_PMD/PMD mappings, we can calculate how many page table pages need > > > to be allocated based on those counters. > > > > > > > > > First, linear alias of the [_text, __init_begin) is not a target for > > > > > > the split and it also seems strange to me to add code inside alloc_init_XXX() > > > > > > that both checks an address range and counts to get the number of block mappings. > > > IIUC, it should be not that hard to exclude kernel mappings. We know > > > kernel_start and kernel_end, so you should be able to maintain a set of > > > counters for kernel, then minus them when you do the calculation for how > > > many page table pages need to be allocated. > > As you said, this is not difficult. However, what I meant was that > > this collection would be done in alloc_init_XXX(), and in that case, > > collecting the number of block mappings for the range > > [kernel_start, kernel_end) and adding conditional logic in > > alloc_init_XXX() seems a bit odd. > > That said, for potential future use cases involving splitting specific ranges, > > I don’t think having this kind of collection is necessarily a bad idea. > > I'm not sure whether we are on the same page or not. IIUC the point is > collecting the counts of PUD/CONT_PMD/PMD by re-walking page table is sub > optimal and unnecessary for this usecase (repainting linear mapping). We can > simply know the counts at linear mapping creation time. What I meant was that the counts collected via dm_meminfo already include kernel aliases, so adding separate code to count kernel aliases again seems odd to me. That said, I do not disagree with the efficiency of using the already collected counts. Thanks! [...] -- Sincerely, Yeoreum Yun