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To: Christoph Lameter Cc: Christoph Hellwig , David Miller , Daniel Borkmann , Andrii Nakryiko , Tejun Heo , Martin KaFai Lau , bpf , Kernel Team , linux-mm , Pekka Enberg , David Rientjes , Joonsoo Kim , Andrew Morton , Vlastimil Babka Content-Type: text/plain; charset="UTF-8" ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1656470954; a=rsa-sha256; cv=none; b=O9GPqJFJX8zVuZYUV1UTkUHogSOWf1/QumucW9FJDUeNdFJok+c7AF0UyAarVedmWSakqO 5XDvaMC8Jw0X1yvVDtv3TCzBHYdtI0fSl7Y3NOYtB3lPwWNX7fmasAHlRLH9ljRi3KKWa+ sK6XvnnS/Vr+n9eftt4jXFbDCgd3e1Q= ARC-Authentication-Results: i=1; imf07.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=RVvz5sv6; spf=pass (imf07.hostedemail.com: domain of alexei.starovoitov@gmail.com designates 209.85.218.43 as permitted sender) smtp.mailfrom=alexei.starovoitov@gmail.com; dmarc=pass (policy=none) header.from=gmail.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1656470954; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=G/Y5+lP8LqqHGKaor3ash/7uQ/mp2B3+t9LF61KTzys=; b=Vx8+8WriS2Rf4O0O9GIjjTcOltVmwPi8YSPkhLx5Imb4JRMdNKbKyjIcKkp/omsng8Wr0U 0UQ6pDTTP2isITYnemB+XNKMXWs+o6z8dRtqqdhWx7PhxKkzVmymvUiVrwthc0Aifp03z/ wKfsM5Qbs1RK/8Ls5/OuL9pE5QWstYw= X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 736D34003D X-Rspam-User: X-Stat-Signature: 5qdf4cxiuz6b39xg8kcnjakqhwxzndd3 Authentication-Results: imf07.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=RVvz5sv6; spf=pass (imf07.hostedemail.com: domain of alexei.starovoitov@gmail.com designates 209.85.218.43 as permitted sender) smtp.mailfrom=alexei.starovoitov@gmail.com; dmarc=pass (policy=none) header.from=gmail.com X-HE-Tag: 1656470954-122061 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Jun 28, 2022 at 7:35 PM Christoph Lameter wrote: > > On Tue, 28 Jun 2022, Alexei Starovoitov wrote: > > > > That is a relatively new feature due to RT logic support. without RT this > > > would be a simple irq disable. > > > > Not just RT. > > It's a slow path: > > if (IS_ENABLED(CONFIG_PREEMPT_RT) || > > unlikely(!object || !slab || !node_match(slab, node))) { > > local_unlock_irqrestore(&s->cpu_slab->lock,...); > > and that's not the only lock in there. > > new_slab->allocate_slab... alloc_pages grabbing more locks. > > > Its not a lock for !RT. > > The fastpath is lockless if hardware allows that but then we go into more > and more serialiation needs as the allocation gets more into the page > allocator logic. On RT fast path == slow path with a lock. On !RT fast path is lock less. That's all correct. bpf side has to make sure safety in all possible paths therefore RT or !RT makes no difference.