From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-la0-f47.google.com (mail-la0-f47.google.com [209.85.215.47]) by kanga.kvack.org (Postfix) with ESMTP id 2C7886B0038 for ; Tue, 25 Nov 2014 06:48:52 -0500 (EST) Received: by mail-la0-f47.google.com with SMTP id hz20so359355lab.6 for ; Tue, 25 Nov 2014 03:48:51 -0800 (PST) Received: from jenni2.inet.fi (mta-out1.inet.fi. [62.71.2.203]) by mx.google.com with ESMTP id qj3si1587722wjc.78.2014.11.25.03.48.50 for ; Tue, 25 Nov 2014 03:48:50 -0800 (PST) Date: Tue, 25 Nov 2014 13:48:46 +0200 From: "Kirill A. Shutemov" Subject: Re: [PATCH] mm: add parameter to disable faultaround Message-ID: <20141125114846.GA10150@node.dhcp.inet.fi> References: <1416898318-17409-1-git-send-email-chanho.min@lge.com> <20141124230502.30f9b6f0.akpm@linux-foundation.org> <547465d2.0937460a.7739.fffff2baSMTPIN_ADDED_BROKEN@mx.google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <547465d2.0937460a.7739.fffff2baSMTPIN_ADDED_BROKEN@mx.google.com> Sender: owner-linux-mm@kvack.org List-ID: To: Chanho Min Cc: 'Andrew Morton' , "'Kirill A. Shutemov'" , 'Hugh Dickins' , 'Michal Hocko' , linux-mm@kvack.org, linux-kernel@vger.kernel.org, 'HyoJun Im' , 'Gunho Lee' , 'Wonhong Kwon' On Tue, Nov 25, 2014 at 08:19:40PM +0900, Chanho Min wrote: > > > The faultaround improves the file read performance, whereas pages which > > > can be dropped by drop_caches are reduced. On some systems, The amount of > > > freeable pages under memory pressure is more important than read > > > performance. > > > > The faultaround pages *are* freeable. Perhaps you meant "free" here. > > > > Please tell us a great deal about the problem which you are trying to > > solve. What sort of system, what sort of workload, what is bad about > > the behaviour which you are observing, etc. > > We are trying to solve two issues. > > We drop page caches by writing to /proc/sys/vm/drop_caches at specific point > and make suspend-to-disk image. The size of this image is increased if faultaround > is worked. drop_caches should never be used outside debugging process. If you use it as part of usual workflow you're doing something wrong. I'm not aware about details on how suspend-to-disk works, but I don't see much point in saving page cache pages into suspend-to-disk image. Dirty pages should be write out and we can read them back after resume on first use. Possible exception is mlocked pages. > Under memory pressure, we want to drop many page caches as possible. > But, The number of dropped pages are reduced compared to non-faultaround kernel. The reason why you see more pages in page cache after drop_pages with faultaround enabled is that drop_pages doesn't touch mapped pages. And with faultaround we obviously have more pages mapped. It's not a reason to have faultaround disable. You should take a closer look on suspend process. -- Kirill A. Shutemov -- 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