From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f41.google.com (mail-wm0-f41.google.com [74.125.82.41]) by kanga.kvack.org (Postfix) with ESMTP id 75E9E6B0254 for ; Fri, 26 Feb 2016 06:41:26 -0500 (EST) Received: by mail-wm0-f41.google.com with SMTP id b205so68642771wmb.1 for ; Fri, 26 Feb 2016 03:41:26 -0800 (PST) Received: from e06smtp10.uk.ibm.com (e06smtp10.uk.ibm.com. [195.75.94.106]) by mx.google.com with ESMTPS id fy9si15482618wjb.72.2016.02.26.03.41.24 for (version=TLS1_2 cipher=AES128-SHA bits=128/128); Fri, 26 Feb 2016 03:41:25 -0800 (PST) Received: from localhost by e06smtp10.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Fri, 26 Feb 2016 11:41:24 -0000 Received: from b06cxnps3074.portsmouth.uk.ibm.com (d06relay09.portsmouth.uk.ibm.com [9.149.109.194]) by d06dlp01.portsmouth.uk.ibm.com (Postfix) with ESMTP id 599C917D8062 for ; Fri, 26 Feb 2016 11:41:43 +0000 (GMT) Received: from d06av06.portsmouth.uk.ibm.com (d06av06.portsmouth.uk.ibm.com [9.149.37.217]) by b06cxnps3074.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id u1QBfKrP57802958 for ; Fri, 26 Feb 2016 11:41:20 GMT Received: from d06av06.portsmouth.uk.ibm.com (localhost [127.0.0.1]) by d06av06.portsmouth.uk.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id u1QBfJX6016582 for ; Fri, 26 Feb 2016 06:41:20 -0500 Date: Fri, 26 Feb 2016 12:41:18 +0100 From: Martin Schwidefsky Subject: Re: [PATCH] thp, mm: remove comments on serializion of THP split vs. gup_fast Message-ID: <20160226124118.41ad93a2@mschwide> In-Reply-To: <20160226110650.GY6356@twins.programming.kicks-ass.net> References: <1456329561-4319-1-git-send-email-kirill.shutemov@linux.intel.com> <20160224185025.65711ed6@thinkpad> <20160225150744.GA19707@node.shutemov.name> <20160226110650.GY6356@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Peter Zijlstra Cc: Hugh Dickins , "Kirill A. Shutemov" , Gerald Schaefer , Steve Capper , Dann Frazier , Catalin Marinas , "Kirill A. Shutemov" , Andrew Morton , Andrea Arcangeli , linux-mm@kvack.org On Fri, 26 Feb 2016 12:06:50 +0100 Peter Zijlstra wrote: > On Thu, Feb 25, 2016 at 10:50:14PM -0800, Hugh Dickins wrote: > > > For example, see the fallback tlb_remove_table_one() in mm/memory.c: > > that one uses smp_call_function() sending IPI to all CPUs concerned, > > without waiting an RCU grace period at all. > > The better comment is with mmu_table_batch. > > Its been too long for me to fully remember, nor have I really paid much > attention to this code in the past few years, so any memory I might have > had might be totally wrong. > > But relying on rcu_read_lock_sched() and friends would mean replacing > that smp_call_function() with synchronize_sched(). That makes sense, just tried that together with a big fat printk to see if we hit that out-of-memory condition in the page table freeing code. The system is swapping like mad but no message so far. > A real quick look at the current code seems to suggest that _might_ just > work, but note that that will be slower, RT and HPC people will like you > for it though. > > So it depends on how hard we hit that special, totally out of memory, > case, and if we care about some performance if we do. If the system is out of memory bad enough for the page allocation to fail an additional synchronize_sched() call probably won't hurt too much. Most of the time we'll be waiting for I/O anyway. -- blue skies, Martin. "Reality continues to ruin my life." - Calvin. -- 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