From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) (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 696803B3894 for ; Fri, 28 Aug 2026 19:17:12 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=216.40.44.15 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787944633; cv=none; b=iUOezwM4pZ64OFI2vXqq+Smd6KXNhgaVNIPmEag/mHAUcuKDNCt8rpvmHR1mJYnXwwwpk5jfeEvAUCrPEbqtvdsQOTfRC2ZL31SQz7GD2O82tm7JZy8V3POgkRirLzYq4lgR8FE94aeYd/w9bYzBb50eEnaoerkWJZ9rACk53Cw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787944633; c=relaxed/simple; bh=OjCe3CktZlYFOQFPLmGRlHo4AyWyH9sO8Gk+RrBAlYI=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=ng0ual3yZb/rNyxXWGKwfdSj3aYJcOWBfqrmtdcgnc5weys/QGyoUI0jXsmYePFtPoK5HZ/F3bYHvjlwFwwvFl4b1e6jT09VsvyCk0/FhmZyXpQVzod2uoKDRo+uM6FUvSVa+v7cx8IJ7F5OnC7jEja2ysdlYeH8S+F/nuU+svU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=goodmis.org; spf=pass smtp.mailfrom=goodmis.org; dkim=pass (1024-bit key) header.d=goodmis.org header.i=@goodmis.org header.b=gAZTVjGD; arc=none smtp.client-ip=216.40.44.15 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=goodmis.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=goodmis.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=goodmis.org header.i=@goodmis.org header.b="gAZTVjGD" Received: from omf05.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay04.hostedemail.com (Postfix) with ESMTP id C52951A053F; Fri, 28 Aug 2026 19:17:06 +0000 (UTC) Received: from [HIDDEN] (Authenticated sender: rostedt@goodmis.org) by omf05.hostedemail.com (Postfix) with ESMTPA id C3E9F20011; Fri, 28 Aug 2026 19:16:57 +0000 (UTC) Date: Fri, 28 Aug 2026 15:17:47 -0400 From: Steven Rostedt To: Sebastian Andrzej Siewior Cc: Peter Zijlstra , 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: <20260828151747.20035d50@gandalf.local.home> In-Reply-To: <20260828151313.5c4a5e4b@gandalf.local.home> 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> X-Mailer: Claws Mail 3.20.0git84 (GTK+ 2.24.33; x86_64-pc-linux-gnu) 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-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: C3E9F20011 X-Stat-Signature: j65tfsnn7wb96ijjjfomjeapo6aro4m7 X-Rspamd-Server: rspamout03 X-Session-Marker: 726F737465647440676F6F646D69732E6F7267 X-Session-ID: U2FsdGVkX1/FRCRqi3s+JC4roW7NUQua3g10tn9P4XM= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=goodmis.org; h=date:from:to:cc:subject:message-id:in-reply-to:references:mime-version:content-type:content-transfer-encoding; s=dkim1; bh=0RDwr71FlsrAMrAAlqln64IM9QGsxwXWA77DtZDfZwQ=; b=gAZTVjGDveN8fhsH4aJV2blL0f0S/QpEEvr3BQpYaHupiEQdLMD69nFOfdLEk1spL0/g6lXtTnfNyIqHZGTSM2GCgE4DvzYvzij8bAWlZRrSpkm67+yI+NJTg387b0JmME/jtx2tEqWIUYUrCD2W7DFVoX4NatssuHtJiesq2nE= X-HE-Tag: 1787944617-357454 X-HE-Meta: U2FsdGVkX1+ViF3OvOgaM5ssQLR7tn0uySWJaFHYtcXWZ21cz7nnxMRW6iHpDWrp6Htrs0cIkgW4SbBQGFpZUf1ROkYnZEWGOtcWKXjDukDAh5xQHzSUkPxJbyaumnTpSqP3YXkkCipkNohafMlloaOqbdI5ACVjC77j7iGbrpU8lCltcFJhtONUqXBCJpw9eTajIr0/aLHn6NisdoeErwIxVK/oB2Np5iYGqcWQEGRVIxOt9i1N8E1VkhWj8uFuSoYqfpNN0eEmhPs7aE8vmz2WPbGl+v4Ry92BAG7LkkOQAqWIZjLFKEu432FqDcWspoc2zzLFnstcV5vVdG65ka7IObsOxeMhd+5KlkygWN4xwraefOr4pQuVKgzS9Rrd On Fri, 28 Aug 2026 15:13:13 -0400 Steven Rostedt wrote: > If one worries about stack size, they may want to turn off > CONFIG_RANDOMIZE_KSTACK_OFFSET as I see some big numbers for do_syscall_64() And the scheduler has some heavy stack usage here! # trace-cmd stack (stack tracer running) Depth Size Location (31 entries) ----- ---- -------- 0) 8120 48 __msecs_to_jiffies+0x9/0x30 1) 8072 104 update_group_capacity+0x94/0x960 2) 7968 528 update_sd_lb_stats.constprop.0+0x426/0x39b0 3) 7440 424 sched_balance_find_src_group+0x8f/0x1150 4) 7016 552 sched_balance_rq+0x934/0x4130 5) 6464 408 pick_task_fair+0xa71/0x1fe0 6) 6056 496 __schedule+0x628/0x76f0 7) 5560 32 schedule+0xde/0x2c0 8) 5528 32 io_schedule+0x8c/0x100 9) 5496 256 rq_qos_wait+0x12b/0x230 10) 5240 136 wbt_wait+0x150/0x260 11) 5104 40 __rq_qos_throttle+0x51/0xa0 12) 5064 304 blk_mq_submit_bio+0xc40/0x28e0 13) 4760 240 submit_bio_noacct_nocheck+0x410/0xb30 14) 4520 40 ext4_io_submit+0xca/0x1a0 15) 4480 144 ext4_bio_write_folio+0x5e2/0x1470 16) 4336 96 mpage_process_page_bufs+0x392/0x700 17) 4240 616 mpage_prepare_extent_to_map+0xaae/0x1120 18) 3624 480 ext4_do_writepages+0x971/0x37f0 19) 3144 312 ext4_writepages+0x2d2/0x610 20) 2832 152 do_writepages+0x21e/0x560 21) 2680 184 __writeback_single_inode+0x119/0x1240 22) 2496 752 writeback_sb_inodes+0x67d/0x17b0 23) 1744 168 __writeback_inodes_wb+0xf2/0x270 24) 1576 304 wb_writeback+0x63e/0x890 25) 1272 320 wb_workfn+0x844/0xca0 26) 952 360 process_one_work+0x8b4/0x15d0 27) 592 176 worker_thread+0x5d3/0xfb0 28) 416 64 kthread+0x33c/0x420 29) 352 160 ret_from_fork+0x65c/0x9e0 30) 192 192 ret_from_fork_asm+0x1a/0x30 Note, I'm running this on my server. That is, this is a production machine. -- Steve