From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751712AbdG1K1q (ORCPT ); Fri, 28 Jul 2017 06:27:46 -0400 Received: from mx2.suse.de ([195.135.220.15]:51493 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751606AbdG1K1p (ORCPT ); Fri, 28 Jul 2017 06:27:45 -0400 Date: Fri, 28 Jul 2017 12:27:43 +0200 From: Michal Hocko To: Mel Gorman Cc: linux-mm@kvack.org, Matthew Wilcox , Vlastimil Babka , Neil Brown , "Theodore Ts'o" , Andrew Morton , LKML Subject: Re: [RFC PATCH] treewide: remove GFP_TEMPORARY allocation flag Message-ID: <20170728102743.GI2274@dhcp22.suse.cz> References: <20170728091904.14627-1-mhocko@kernel.org> <20170728095249.n62p5nhqbekjd5yn@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170728095249.n62p5nhqbekjd5yn@suse.de> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 28-07-17 10:52:49, Mel Gorman wrote: > On Fri, Jul 28, 2017 at 11:19:04AM +0200, Michal Hocko wrote: > > From: Michal Hocko > > > > GFP_TEMPORARY has been introduced by e12ba74d8ff3 ("Group short-lived > > and reclaimable kernel allocations") along with __GFP_RECLAIMABLE. It's > > primary motivation was to allow users to tell that an allocation is > > short lived and so the allocator can try to place such allocations close > > together and prevent long term fragmentation. As much as this sounds > > like a reasonable semantic it becomes much less clear when to use the > > highlevel GFP_TEMPORARY allocation flag. How long is temporary? Can > > the context holding that memory sleep? Can it take locks? It seems > > there is no good answer for those questions. > > > > The current implementation of GFP_TEMPORARY is basically > > GFP_KERNEL | __GFP_RECLAIMABLE which in itself is tricky because > > basically none of the existing caller provide a way to reclaim the > > allocated memory. So this is rather misleading and hard to evaluate for > > any benefits. > > > > At the time of the introduction, the users were all very short-lived > where short was for operations such as reading a proc file that discarded > buffers afterwards. Maybe we can add a special slab cache for those? > However, it does seem to have misused over the last > few years and it was too easy to confuse "temporary" with "short lived" > and too easy to get confused about "how short lived is short lived?". On > that basis; > > Acked-by: Mel Gorman Thanks! -- Michal Hocko SUSE Labs