From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f69.google.com (mail-wm0-f69.google.com [74.125.82.69]) by kanga.kvack.org (Postfix) with ESMTP id AEBBA6B0007 for ; Mon, 19 Feb 2018 09:42:20 -0500 (EST) Received: by mail-wm0-f69.google.com with SMTP id e143so4354798wma.2 for ; Mon, 19 Feb 2018 06:42:20 -0800 (PST) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id s3si5589020wra.67.2018.02.19.06.42.19 for (version=TLS1 cipher=AES128-SHA bits=128/128); Mon, 19 Feb 2018 06:42:19 -0800 (PST) Date: Mon, 19 Feb 2018 15:42:16 +0100 From: Michal Hocko Subject: Re: [RFC 1/2] Protect larger order pages from breaking up Message-ID: <20180219144216.GP21134@dhcp22.suse.cz> References: <20180216160110.641666320@linux.com> <20180216160121.519788537@linux.com> <20180219101935.cb3gnkbjimn5hbud@techsingularity.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180219101935.cb3gnkbjimn5hbud@techsingularity.net> Sender: owner-linux-mm@kvack.org List-ID: To: Mel Gorman Cc: Christoph Lameter , Matthew Wilcox , linux-mm@kvack.org, linux-rdma@vger.kernel.org, akpm@linux-foundation.org, Thomas Schoebel-Theuer , andi@firstfloor.org, Rik van Riel , Guy Shattah , Anshuman Khandual , Michal Nazarewicz , Vlastimil Babka , David Nellans , Laura Abbott , Pavel Machek , Dave Hansen , Mike Kravetz On Mon 19-02-18 10:19:35, Mel Gorman wrote: [...] > Access to the pool is unprotected so you might create a reserve for jumbo > frames only to have them consumed by something else entirely. It's not > clear if that is even fixable as GFP flags are too coarse. > > It is not covered in the changelog why MIGRATE_HIGHATOMIC was not > sufficient for jumbo frames which are generally expected to be allocated > from atomic context. If there is a problem there then maybe > MIGRATE_HIGHATOMIC should be made more strict instead of a hack like > this. It'll be very difficult, if not impossible, for this to be tuned > properly. > > Finally, while I accept that fragmentation over time is a problem for > unmovable allocations (fragmentation protection was originally designed > for THP/hugetlbfs), this is papering over the problem. If greater > protections are needed then the right approach is to be more strict about > fallbacks. Specifically, unmovable allocations should migrate all movable > pages out of migrate_unmovable pageblocks before falling back and that > can be controlled by policy due to the overhead of migration. For atomic > allocations, allow fallback but use kcompact or a workqueue to migrate > movable pages out of migrate_unmovable pageblocks to limit fallbacks in > the future. Completely agreed! > I'm not a fan of this patch. Yes, I think the approach is just wrong. It will just hit all sorts of weird corner cases and won't work reliable for those who care. -- Michal Hocko SUSE Labs -- 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