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t=1776763625; bh=MR/GwJdH+bPFnJA+jLQ/+UtlUiXYet/1ZH/US7v3bHE=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=Lm8NxsWtNqVyR+muCCnRFtHlpHTjvsA01spMNnq0NEPA9JbrqgrK7fsn7nJQctOph 4I2w+QkPdRXDO8IUCvVMv0h95A1KrZy5QWxGRg4uaJK1MNS0OEpOQbJN2N6McpSu36 FDx3JdDMTUQNzwGkKKGQNLpFGlPelpPFddNM+MuiaZy7pSJ1KLgamqL3ZmIpobmiVX Qs83No089Dt+C4YANol96fE1BFYW2cF+LYu82ot0qUr8UK6bMHWLwgWwjJMP+pBZq4 bSKOvJdyNs8332tAB2cYTby9Eh78OHkOhL0uxanWJUaHSt+1aLGOdK8ggPRpGQ6Bl3 xD52IqviaC9sQ== Message-ID: <378ae036-6559-4b81-9bac-c8f0b73e1c98@kernel.org> Date: Tue, 21 Apr 2026 11:27:00 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] mm/page_alloc: use batch page clearing in kernel_init_pages() Content-Language: en-US To: Hrushikesh Salunke , akpm@linux-foundation.org, david@kernel.org, ljs@kernel.org, Liam.Howlett@oracle.com, 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: <20260421042451.76918-1-hsalunke@amd.com> From: "Vlastimil Babka (SUSE)" In-Reply-To: <20260421042451.76918-1-hsalunke@amd.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 19D8940008 X-Stat-Signature: g9kti5aickxfayb4up8mfk31rw6ag1yw X-Rspam-User: X-Rspamd-Server: rspam09 X-HE-Tag: 1776763626-735739 X-HE-Meta: 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 PpcCpwvZ AJu45I81GQqP5YI8nnhqtuDbWHoflXwezmntGSNtjr9P8bHJI0pViGO4uuUbSbzuF+8Yt3CnYTsmPsOCiKZcfYstmJ/GsbjkETxTdL3UYnj0JC09dM7dYlSrM08yCFYnGW/EUsjQUWe4jfsNl0URDWnR0XRgBeQX15GLGYhotHZgrhir0fxrujf3msNmOYfzovrJXXsMfWO93M45/0f9ORS4Qs5O2bGOo4IUrZ7PvhcQ55d7hHOf0hAZ7/L/yQ2Rrv0R5V0KrjkrzYPwdGdQkaOpnFw7sVqhCzS7HoBgUozCUkDhkxFTA6zooC/tqS5BnJAov+rpm+Go7KK+efiblLcTv/pihgSfc8/P9 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 4/21/26 06:24, 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. > > Use it in kernel_init_pages() to replace the per-page loop. > > 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% > > Signed-off-by: Hrushikesh Salunke > --- > base commit: f1541b40cd422d7e22273be9b7e9edfc9ea4f0d7 > > v1: https://lore.kernel.org/all/20260408092441.435133-1-hsalunke@amd.com/ > > Changes since v1: > - Dropped cond_resched() and PROCESS_PAGES_NON_PREEMPT_BATCH as > kernel_init_pages() runs inside the page allocator and can be > called from atomic context, making cond_resched() unsafe. The > original code never had a cond_resched() here, and the > performance gain comes from batching, not rescheduling. > > - Moved the !HIGHMEM/HIGHMEM branching into a new > clear_highpages_kasan_tagged() helper in highmem.h, per David's > suggestion. > > include/linux/highmem.h | 12 ++++++++++++ > mm/page_alloc.c | 5 +---- > 2 files changed, 13 insertions(+), 4 deletions(-) Acked-by: Vlastimil Babka (SUSE) > > diff --git a/include/linux/highmem.h b/include/linux/highmem.h > index af03db851a1d..ad0f42d06ce6 100644 > --- a/include/linux/highmem.h > +++ b/include/linux/highmem.h > @@ -345,6 +345,18 @@ static inline void clear_highpage_kasan_tagged(struct page *page) > kunmap_local(kaddr); > } > > +static inline void clear_highpages_kasan_tagged(struct page *page, int numpages) > +{ > + if (!IS_ENABLED(CONFIG_HIGHMEM)) { > + clear_pages(kasan_reset_tag(page_address(page)), numpages); > + } else { > + int i; > + > + for (i = 0; i < numpages; i++) > + clear_highpage_kasan_tagged(page + i); > + } > +} > + > #ifndef __HAVE_ARCH_TAG_CLEAR_HIGHPAGES > > /* Return false to let people know we did not initialize the pages */ > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index b1c5430cad4e..1aaf7f839ff4 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -1220,12 +1220,9 @@ static inline bool should_skip_kasan_poison(struct page *page) > > static void kernel_init_pages(struct page *page, int numpages) > { > - int i; > - > /* s390's use of memset() could override KASAN redzones. */ > kasan_disable_current(); > - for (i = 0; i < numpages; i++) > - clear_highpage_kasan_tagged(page + i); > + clear_highpages_kasan_tagged(page, numpages); > kasan_enable_current(); > } >