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b=aEyfOAJ0gD3wAl9oC0a8NTWIbaNvFiVVSppPD+t2m6hrhSKnzBmAIBcBWFxEJhM24 moMFkwtxtrLzGEFreyfwnwjsGROFT2hMMf1wFHHKybyhXCJqTMz9Ox+RPVBkeUoxHc 8ArQ8tN+CorcLAQVvwhsY2QQ3Wy+bk0kKfnEiK2L88LlOJmKHN253HUYT2HdtuVlB8 DO5WoBc+LKdxkwHVV2JEyyZsvozErLyWDK49Vd7JGTqHJziEhrw+cora0uBHW3jgO6 biWyUQ5XO9gsCKE8iMnRuQsxsdEbO9dzBOj1etJGvui47LAz/qkRaLXa5mpJZupysK qU2G9oVXQ6l2g== Message-ID: Date: Tue, 28 Apr 2026 09:06:14 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3] mm/page_alloc: replace kernel_init_pages() with batch page clearing To: "Salunke, Hrushikesh" , Andrew Morton Cc: ljs@kernel.org, Liam.Howlett@oracle.com, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, jackmanb@google.com, hannes@cmpxchg.org, ziy@nvidia.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, rkodsara@amd.com, bharata@amd.com, ankur.a.arora@oracle.com, shivankg@amd.com References: <20260422102729.166599-1-hsalunke@amd.com> <20260423041249.156eb95889696ccfaf23dca1@linux-foundation.org> <1253ca14-69de-418f-8f94-b08e8105e924@kernel.org> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: C59838000B X-Rspam-User: X-Stat-Signature: 9wphfa74kqzyfpcwgfon4bk81r99uqzk X-HE-Tag: 1777359982-66909 X-HE-Meta: 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 zJ/wRhio 1J0HVnMmycL8gRTEfwPXbvxZYP2GpQ9eFJ06rqyul3FBXfjBCA5vYouX90dle0NWzB5jgzBnJ2xXQFsEI5UZRkgy1YdaJDk7k9oHX0Q8C5JVAeqNE85GdZrqkS8qWrddRfJwJv0gADmudS6ESTLWcwXg06YRL5hjbb1dHwDAlUcD1+SoZ8PbkNIDgNS0YdJm/vC5xcfCQmjvz1y2Mj/uth0NfeUgeD7CNTtBqHX3JXt/c1lerJiehL2oJz8+deLFuaYnhnDcrMmha2YwgtRDWwOHjgguomidO+DQxPGbng4T0O73paSmmQ0Hkjg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 4/28/26 05:55, Salunke, Hrushikesh wrote: > > On 24-04-2026 14:22, David Hildenbrand (Arm) wrote: >> Caution: This message originated from an External Source. Use proper caution when opening attachments, clicking links, or responding. >> >> >> On 4/24/26 10:42, Salunke, Hrushikesh wrote: >>> Hi Andrew, >>> >>> The idea was to keep it alongside clear_highpage_kasan_tagged() as its >>> batch counterpart, but currently it is only used by page_alloc.c. >> Right. >> >> Looking at init_vmalloc_pages(), I wonder if it could also benefit from batching >> if we find that pages are actually contiguous. >> >> That would require looking up multiple pages at once. vmalloc_to_pages() or sth >> like that. Surely, doing such an optimized page table walk could be beneficial >> by itself. > > Interesting idea. For the general case where we only have struct page > pointers, we'd need physical contiguity detection and a batched page > table walk as you described. But looking at init_vmalloc_pages() > specifically, it already has the vmalloc virtual address which is > contiguous, so can we just do following and potentially skip the > vmalloc_to_page() walk entirely: > > clear_pages(kasan_reset_tag((void *)start), size >> PAGE_SHIFT); > > What do you think? would this simpler approach work > , or am I missing something? Good question. :) That way you'd be operating on the vmalloc address range, not on the direct map. Is the vmalloc address range guaranteed to be writable at that point? -- Cheers, David