From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1924D3B8BCC; Mon, 31 Aug 2026 07:08:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.92.199 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788160083; cv=none; b=hkmHNnZDKT/9EQnadI5zW57m0L2PpdtLC0mKXAjduVR8LtWhqhDYxvDhwB8e09v7dlBMUalZ+VtaPiRVMMxWRO2DbRpquke8Xm4kMJRUtwSvpvJMS5vwYl4B6T/7aqTciqe7OC5X4c/dYdElyhmLLIH5pgMdLsB8ykBcZONcv+w= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788160083; c=relaxed/simple; bh=0WIM+qPhrT5aBolDJz4drM60KG4zXVaG7M7RJypKEeM=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=G8OTBmAVOyBXwQTDyPH3s6InQq9iUbSxRZOIYuNduct6Hy3ISAnnjzPrBzYTAXlVnUZ4bfXsYmnXZebYoBMc23isaOneL2mQ1wK7fG14jVnpfRay8hNlnRkVd9pgwwpVdyndnJsBhVnZK7yTp/tYlD8ra0q5drDcvrmqeehdupw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=pass smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=a67/WBXc; arc=none smtp.client-ip=90.155.92.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="a67/WBXc" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=rlHsLIomUZDuyupnnAtNJaCHYl4a5Rg7e9MyiEzSdUU=; b=a67/WBXciwwfTXKyxpcVqnkgrD AlJwjFjl6pELrCGWf+akgeocN9/XKhybGbgvTSS9Zx5nrvlXfgo2SBaz14PrrOZPS2VukRTfhD/q6 Jfr/OkRBqX0gkCPkMqhchghylTHtfrNvF52sQ+iAYXZbgLQaIpyZ/xgqDRNwxVXvgKMeQfd8kuRAF A8SN9TtFhnhAFtadO1lcrnkSC0ny7YBwnc8+GDgsWrgg06hTDeGotwS9qoQdZKgI50gJWin2KZt6a +qD2ksvaqTbKHuXTK4U/3I7+FKvGqy6LrTtZznalbKweNDNmLTET1K6dItlPFsOZHxPKP0vvF9ZXo iSIhEE9A==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.99.2 #2 (Red Hat Linux)) id 1x0w7E-00000009b4c-0xtJ; Mon, 31 Aug 2026 07:07:36 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 26E203002D8; Mon, 31 Aug 2026 09:07:33 +0200 (CEST) Date: Mon, 31 Aug 2026 09:07:33 +0200 From: Peter Zijlstra To: Sebastian Andrzej Siewior Cc: Steven Rostedt , David Stevens , Catalin Marinas , Will Deacon , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H . Peter Anvin" , Andrew Morton , Dave Chinner , Qi Zheng , Roman Gushchin , Muchun Song , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Ben Segall , Mel Gorman , Valentin Schneider , K Prateek Nayak , Uladzislau Rezki , David Hildenbrand , Lorenzo Stoakes , "Liam R . Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Kees Cook , Clark Williams , suleiman@google.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-rt-devel@lists.linux.dev Subject: Re: [RFC 06/10] Reclaim memory from blocked kernel stacks Message-ID: <20260831070733.GS687043@noisy.programming.kicks-ass.net> References: <20260827232948.2520558-1-stevensd@google.com> <20260827232948.2520558-7-stevensd@google.com> <20260828133620._x2XfJR_@linutronix.de> <20260828135947.GU776954@noisy.programming.kicks-ass.net> <20260828151018.HnR9xV1N@linutronix.de> <20260828150836.2d5b378c@gandalf.local.home> <20260828151313.5c4a5e4b@gandalf.local.home> <20260828151747.20035d50@gandalf.local.home> <20260831065509.qqEtERDB@linutronix.de> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260831065509.qqEtERDB@linutronix.de> On Mon, Aug 31, 2026 at 08:55:09AM +0200, Sebastian Andrzej Siewior wrote: > (stack tracer running) > Depth Size Location (60 entries) > ----- ---- -------- > 0) 8176 48 __css_rstat_updated+0x9/0x150 > 1) 8128 8 __cgroup_account_cputime+0x2f/0x50 > 2) 8120 48 update_se+0x10c/0x1b0 > 3) 8072 48 update_curr+0x31/0x180 > 4) 8024 56 put_prev_entity+0x153/0x1f0 > 5) 7968 136 pick_next_task_fair+0x684/0x8e0 > 6) 7832 120 __schedule+0x1ca/0x1130 > 7) 7712 8 preempt_schedule_irq+0x38/0x60 > 8) 7704 72 irqentry_exit+0x148/0x6b0 > 9) 7632 136 asm_sysvec_apic_timer_interrupt+0x1a/0x20 > 10) 7496 240 HUF_compress1X_usingCTable_internal_bmi2+0x12d2/0x1c40 > > Does this stack tracer distinguish between the kernel-stack and > IRQ-stack? I would expect asm_sysvec_apic_timer_interrupt() on the > IRQ-stack and not adding weight to the kernel stack. This is the return from interrupt path, irqentry_exit() is right after we switch back from the IRQ stack and are back on the task stack. We have to be, in order to schedule the task and all that.