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From: Muchun Song In-Reply-To: <35B81EA5-D719-4FC4-93C5-674DD5BFDA4F@linux.dev> Date: Thu, 22 Jan 2026 19:42:47 +0800 Cc: Andrew Morton , David Hildenbrand , Matthew Wilcox , Usama Arif , Frank van der Linden , Oscar Salvador , Mike Rapoport , Vlastimil Babka , Lorenzo Stoakes , Zi Yan , Baoquan He , Michal Hocko , Johannes Weiner , Jonathan Corbet , kernel-team@meta.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org Content-Transfer-Encoding: quoted-printable Message-Id: <45434FC3-455E-4CE8-9F43-F398D5EC73A9@linux.dev> References: <20260121162253.2216580-1-kas@kernel.org> <20260121162253.2216580-8-kas@kernel.org> <71F051F2-5F3B-40A5-9347-BA2D93F2FF3F@linux.dev> <35B81EA5-D719-4FC4-93C5-674DD5BFDA4F@linux.dev> To: Kiryl Shutsemau X-Migadu-Flow: FLOW_OUT > On Jan 22, 2026, at 19:33, Muchun Song wrote: >=20 >=20 >=20 >> On Jan 22, 2026, at 19:28, Kiryl Shutsemau wrote: >>=20 >> On Thu, Jan 22, 2026 at 11:10:26AM +0800, Muchun Song wrote: >>>=20 >>>=20 >>>> On Jan 22, 2026, at 00:22, Kiryl Shutsemau wrote: >>>>=20 >>>> If page->compound_info encodes a mask, it is expected that memmap = to be >>>> naturally aligned to the maximum folio size. >>>>=20 >>>> Add a warning if it is not. >>>>=20 >>>> A warning is sufficient as MAX_FOLIO_ORDER is very rarely used, so = the >>>> kernel is still likely to be functional if this strict check fails. >>>>=20 >>>> Signed-off-by: Kiryl Shutsemau >>>> --- >>>> include/linux/mmzone.h | 1 + >>>> mm/sparse.c | 5 +++++ >>>> 2 files changed, 6 insertions(+) >>>>=20 >>>> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h >>>> index 390ce11b3765..7e4f69b9d760 100644 >>>> --- a/include/linux/mmzone.h >>>> +++ b/include/linux/mmzone.h >>>> @@ -91,6 +91,7 @@ >>>> #endif >>>>=20 >>>> #define MAX_FOLIO_NR_PAGES (1UL << MAX_FOLIO_ORDER) >>>> +#define MAX_FOLIO_SIZE (PAGE_SIZE << MAX_FOLIO_ORDER) >>>>=20 >>>> enum migratetype { >>>> MIGRATE_UNMOVABLE, >>>> diff --git a/mm/sparse.c b/mm/sparse.c >>>> index 17c50a6415c2..5f41a3edcc24 100644 >>>> --- a/mm/sparse.c >>>> +++ b/mm/sparse.c >>>> @@ -600,6 +600,11 @@ void __init sparse_init(void) >>>> BUILD_BUG_ON(!is_power_of_2(sizeof(struct mem_section))); >>>> memblocks_present(); >>>>=20 >>>> + if (compound_info_has_mask()) { >>>> + WARN_ON(!IS_ALIGNED((unsigned long)pfn_to_page(0), >>>> + MAX_FOLIO_SIZE / sizeof(struct page))); >>>=20 >>> I still have concerns about this. If certain architectures or = configurations, >>> especially when KASLR is enabled, do not meet the requirements = during the >>> boot stage, only specific folios larger than a certain size might = end up with >>> incorrect struct page entries as the system runs. How can we detect = issues >>> arising from either updating the struct page or making incorrect = logical >>> judgments based on information retrieved from the struct page? >>>=20 >>> After all, when we see this warning, we don't know when or if a = problem will >>> occur in the future. It's like a time bomb in the system, isn't it? = Therefore, >>> I would like to add a warning check to the memory allocation place, = for >>> example:=20 >>>=20 >>> WARN_ON(!IS_ALIGNED((unsigned long)&folio->page, folio_size / = sizeof(struct page))); >>=20 >> I don't think it is needed. Any compound page usage would trigger the >> problem. It should happen pretty early. >=20 > Why would you think it would be discovered early? If the alignment of = struct page > can only meet the needs of 4M pages (i.e., the largest pages that = buddy can > allocate), how can you be sure that there will be a similar path using = CMA > early on if the system allocates through CMA in the future (after all, = CMA > is used much less than buddy)? Suppose we are more aggressive. If the alignment requirement of struct = page cannot meet the needs of 2GB pages (which is an uncommon memory = allocation requirement), then users might not care about such a warning message = after the system boots. And if there is no allocation of pages greater than or equal to 2GB for a period of time in the future, the system will have no problems. But once some path allocates pages greater than or equal to = 2GB, the system will go into chaos. And by that time, the system log may no longer have this warning message. Is that not the case? >=20 >>=20 >> --=20 >> Kiryl Shutsemau / Kirill A. Shutemov