From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-f170.google.com (mail-wi0-f170.google.com [209.85.212.170]) by kanga.kvack.org (Postfix) with ESMTP id 296906B0087 for ; Fri, 29 May 2015 15:12:18 -0400 (EDT) Received: by wicmx19 with SMTP id mx19so23963465wic.0 for ; Fri, 29 May 2015 12:12:17 -0700 (PDT) Received: from gum.cmpxchg.org (gum.cmpxchg.org. [85.214.110.215]) by mx.google.com with ESMTPS id cy1si5156885wib.89.2015.05.29.12.12.15 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 29 May 2015 12:12:16 -0700 (PDT) Date: Fri, 29 May 2015 15:11:59 -0400 From: Johannes Weiner Subject: Re: [RFC] mm: change irqs_disabled() test to spin_is_locked() in mem_cgroup_swapout Message-ID: <20150529191159.GA29078@cmpxchg.org> References: <20150529104815.2d2e880c@sluggy> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150529104815.2d2e880c@sluggy> Sender: owner-linux-mm@kvack.org List-ID: To: Clark Williams Cc: Thomas Gleixner , linux-mm@kvack.org, Andrew Morton , RT , Fernando Lopez-Lezcano , Steven Rostedt , Sebastian Andrzej Siewior Hi Clark, On Fri, May 29, 2015 at 10:48:15AM -0500, Clark Williams wrote: > @@ -5845,7 +5845,7 @@ void mem_cgroup_swapout(struct page *page, > swp_entry_t entry) page_counter_uncharge(&memcg->memory, 1); > > /* XXX: caller holds IRQ-safe mapping->tree_lock */ > - VM_BUG_ON(!irqs_disabled()); > + VM_BUG_ON(!spin_is_locked(&page_mapping(page)->tree_lock)); > > mem_cgroup_charge_statistics(memcg, page, -1); It's not about the lock, it's about preemption. The charge statistics use __this_cpu operations and they're updated from process context and interrupt context both. This function really should do a local_irq_save(). I only added the VM_BUG_ON() to document that we know the caller is holding an IRQ-safe lock and so we don't need to bother with another level of IRQ saving. So how does this translate to RT? I don't know. But if switching to explicit IRQ toggling would help you guys out we can do that. It is in the swapout path after all, the optimization isn't that important. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org