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t=1776939213; bh=XDlDi3Pv1jl/HlvTUqd6zWFMsv9KVgXtFB4DW2Jg2p4=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=Kq14zpXLceZVZqU9nU01Lo7qXH5inYqlAF3bJhOl3xuP1u8kkE0xxjQ2u4xtHpv+J rI1FC6UyvO60E9RjcU8gBwhEYizuiSL+uc4Mi6i3aoirCReDGNQtpP//9XcVTZ4Rld Slp06FxpF2ai4pE8rZe34mIA4YMmQOrC3cty1YhUSRCQkCYTPfJdjhLcwjkZJioLuZ 6I2WTIek9RQpjr0bXswQYNF+FbyKjCnR/KpjwLPWnYnyS6pkPVJEu78jRz/R4MR+Je Owu7i7SjhRI9eshL9ZsT5c8C75Lz5ZYcX9tNSAxoW1e0lAQI9RZJlvSc6gqqQoGIqw KjdIX3rkucbGw== Message-ID: <6704f990-6c52-4c83-9fac-ede4c7af37b0@kernel.org> Date: Thu, 23 Apr 2026 12:13:26 +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" , akpm@linux-foundation.org, 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 Cc: 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> <5eb58895-b9c2-4124-aec7-e55074c372d5@amd.com> 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-Queue-Id: A6496180004 X-Stat-Signature: 6ni3hzqyfy577u74x3xh7bwnm93fwrj4 X-Rspam-User: X-Rspamd-Server: rspam09 X-HE-Tag: 1776939214-865501 X-HE-Meta: U2FsdGVkX1+38cZHRvRaHb7NcsrDtl8EkBXcEv4y+P7F9JejtOPpNz2oHSTubyppgH4ThTgIlPXG7UmvVKGvl8UQWk16CBrJrwrB5wRurT4m7QVqiMEHns8cW6CCBxkBjM9X7UDEleZ0KBqAtmlHZ1dhVI38awpilQepXZ7dUNec/44FUobzCzgKY3CDahMLKDr3YwvoVWhZXNgvk6hBGe4yk6kJq2IpfDre4PhjH1B8Hy+mzVHPlWVRefXY3j8P6IMzFnhCKcq81+qrNN3rIkAWxz/PxIULSNwQXZ+Cxi6Q2qdHUQjlyeNTdMgeWzLPMcKojVQCacs4Vw8dPFhJQMpYCdi5PXFuLkKkzmJc9qYv6nVhMRrTAZuNm7r/cQGwoCMBoUQKHJld7EUcd4IyjH+DvPJ06Mm/NAygoxEBRQ6R7dxC5kytchUyOu5+AhL9dcylrAMpAh/SWo37WtAcK67ETDguKosiGcmfbVeiG+iV8JSyG1zfLJO2q4tihIgW2W6t3uQX1yCLuHpIwl1LmeIHN04V20s1iXhU3KbJH1jxfzyGgbd5zZ3xZsCX9w3qY7m0UaIB6vjg+zeHozJzQfISaTWd9k3WC6fTlSnhGnG+/V9/b3fLAEGGo+n27UlOfQv3DOE7MzcNVRwZzuy+PXs0LQ3AavqVHNyBm8EuxC9+WnWaetvvJaEjMTnjTkAhViU400ZR2zpzH4VcXqJDmaR2suh0K79yXzL6xd7VRYKF442Y2P6rc46h2ipeaTNRlCvNpExPBkkK60M9MIut9RD3Tmdbefm4ejKRVuX+UVi8V6rKbe0mqWl6TCazcepzxpiPk/QObhMEBIW1AetM4pZkhi/gXIrA7zguvzENH10JS4Z55fkhJYV4cuXF123L6JAuZZtv6EelANHsPxIZnW6ydECWwusdXZL1iROCGjUU7ZscgBPnpN99s3+/3IybzMjbvH1H4LJDrs1MvbW z9S3uQa0 VcDT2o+mBXBIJHxjbZS1pc/u7drulclpVxoF+hb+cWw3yoKu3YdMPbj7SWfS866hDSg1fN6HZ9jeHJnymv7BhC25omgkde6LiwcMmHw/g8BIXLDRwVXTrp0PdyQQKxFP4xXPczK7Orbxn4jWsF4F9ZhlriAdiuHNKDPr/3g3wkfQHGL2bu0NhCmnxqybOXuIqogUUTpyNlW464jHxKdsflwO+SXVcWwc6b8sAjJRv5nhqCByF8E56uuXcjza0DyrMfxwrfNRrRVgv/HGSWl6BPuwfydwUJ3vcCUjiqPxoiejZK+OQ/EX2vDCJI5g1k2Cda91nhTn4WYi2bUg= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 4/23/26 07:09, Salunke, Hrushikesh wrote: > > On 22-04-2026 23:55, David Hildenbrand (Arm) wrote: >> Caution: This message originated from an External Source. Use proper caution when opening attachments, clicking links, or responding. >> >> >> On 4/22/26 12:26, Hrushikesh Salunke wrote: >>> When init_on_alloc is enabled, kernel_init_pages() clears every page >>> one at a time via clear_highpage_kasan_tagged(), which incurs per-page >>> kmap_local_page()/kunmap_local() overhead and prevents the architecture >>> clearing primitive from operating on contiguous ranges. >>> >>> Introduce clear_highpages_kasan_tagged() in highmem.h, a batch >>> clearing helper that calls clear_pages() for the full contiguous range >>> on !HIGHMEM systems, bypassing the per-page kmap overhead and allowing >>> a single invocation of the arch clearing primitive across the entire >>> allocation. The HIGHMEM path falls back to per-page clearing since >>> those pages require kmap. >>> >>> Replace kernel_init_pages() with direct calls to the new helper, as it >>> becomes a trivial wrapper. >>> >>> Allocating 8192 x 2MB HugeTLB pages (16GB) with init_on_alloc=1: >>> >>> Before: 0.445s >>> After: 0.166s (-62.7%, 2.68x faster) >>> >>> Kernel time (sys) reduction per workload with init_on_alloc=1: >>> >>> Workload Before After Change >>> Graph500 64C128T 30m 41.8s 15m 14.8s -50.3% >>> Graph500 16C32T 15m 56.7s 9m 43.7s -39.0% >>> Pagerank 32T 1m 58.5s 1m 12.8s -38.5% >>> Pagerank 128T 2m 36.3s 1m 40.4s -35.7% >> We do have some elaborate handling in clear_contig_highpages() to chunk it up >> (and to call cond_resched()). But that function can get called with much bigger >> ranges. >> >> I'm not concerned about the cond_resched() -- we wouldn't do one here before -- >> but I'm wondering whether we could end up triggering a HW instruction that is >> uninterruptible and takes a rather long time. >> >> But clear_contig_highpages() breaks it into 32MiB chunks, and only x86 supports >> it so far. So we won't exceed that with the maximum buddy order of 4MiB on x86. >> >> Acked-by: David Hildenbrand (Arm) >> >> -- >> Cheers, >> >> David > > Right, on x86 the max buddy order keeps it well within safe limits. > > Also, rep stosb/stosq on x86, currently used for clearing, is > interruptible, the CPU can take interrupts between iterations and > resume where it left off. Ah yes, indeed! -- Cheers, David