From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pb0-f51.google.com (mail-pb0-f51.google.com [209.85.160.51]) by kanga.kvack.org (Postfix) with ESMTP id 1FA696B012C for ; Mon, 9 Dec 2013 18:22:05 -0500 (EST) Received: by mail-pb0-f51.google.com with SMTP id up15so6366259pbc.38 for ; Mon, 09 Dec 2013 15:22:04 -0800 (PST) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org. [140.211.169.12]) by mx.google.com with ESMTP id yd9si8590599pab.321.2013.12.09.15.22.03 for ; Mon, 09 Dec 2013 15:22:03 -0800 (PST) Date: Mon, 9 Dec 2013 15:22:02 -0800 From: Andrew Morton Subject: Re: [patch] mm, page_alloc: make __GFP_NOFAIL really not fail Message-Id: <20131209152202.df3d4051d7dc61ada7c420a9@linux-foundation.org> In-Reply-To: References: Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: David Rientjes Cc: Mel Gorman , Michal Hocko , linux-kernel@vger.kernel.org, linux-mm@kvack.org On Mon, 9 Dec 2013 13:56:37 -0800 (PST) David Rientjes wrote: > __GFP_NOFAIL specifies that the page allocator cannot fail to return > memory. Allocators that call it may not even check for NULL upon > returning. > > It turns out GFP_NOWAIT | __GFP_NOFAIL or GFP_ATOMIC | __GFP_NOFAIL can > actually return NULL. More interestingly, processes that are doing > direct reclaim and have PF_MEMALLOC set may also return NULL for any > __GFP_NOFAIL allocation. __GFP_NOFAIL is a nasty thing and making it pretend to work even better is heading in the wrong direction, surely? It would be saner to just disallow these even-sillier combinations. Can we fix up the current callers then stick a WARN_ON() in there? > This patch fixes it so that the page allocator never actually returns > NULL as expected for __GFP_NOFAIL. It turns out that no code actually > does anything as crazy as GFP_ATOMIC | __GFP_NOFAIL currently, so this > is more for correctness than a bug fix for that issue. -- 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