Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753117AbcD1Nb7 (ORCPT ); Thu, 28 Apr 2016 09:31:59 -0400 Received: from mail-wm0-f53.google.com ([74.125.82.53]:35128 "EHLO mail-wm0-f53.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752463AbcD1NYS (ORCPT ); Thu, 28 Apr 2016 09:24:18 -0400 From: Michal Hocko To: Andrew Morton Cc: , LKML , Andy Lutomirski , Benjamin Herrenschmidt , Catalin Marinas , Chen Liqin , Chris Metcalf , "David S. Miller" , Guan Xuetao , Heiko Carstens , Helge Deller , "H. Peter Anvin" , Ingo Molnar , "James E.J. Bottomley" , John Crispin , Lennox Wu , Ley Foon Tan , Martin Schwidefsky , Matt Fleming , Michal Hocko , Mikulas Patocka , Rich Felker , Russell King , Shaohua Li , "Theodore Ts'o" , Thomas Gleixner , Vineet Gupta , Will Deacon , Yoshinori Sato Subject: [PATCH 0/19] get rid of superfluous __GFP_REPEAT Date: Thu, 28 Apr 2016 15:23:46 +0200 Message-Id: <1461849846-27209-1-git-send-email-mhocko@kernel.org> X-Mailer: git-send-email 2.8.0.rc3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2842 Lines: 56 Hi, this is the thrid version of the patchset previously sent [1]. I have basically only rebased it on top of next-20160428 tree and dropped "crypto: get rid of superfluous __GFP_REPEAT" which went through crypto tree. I have added two more md patches as I couldn't resist more alloc related cleanups at that area. Motivation: While working on something unrelated I've checked the current usage of __GFP_REPEAT in the tree. It seems that a majority of the usage is and always has been bogus because __GFP_REPEAT has always been about costly high order allocations while we are using it for order-0 or very small orders very often. It seems that a big pile of them is just a copy&paste when a code has been adopted from one arch to another. I think it makes some sense to get rid of them because they are just making the semantic more unclear. Please note that GFP_REPEAT is documented as * __GFP_REPEAT: Try hard to allocate the memory, but the allocation attempt * _might_ fail. This depends upon the particular VM implementation. while !costly requests have basically nofail semantic. So one could reasonably expect that order-0 request with __GFP_REPEAT will not loop for ever. This is not implemented right now though. I would like to move on with __GFP_REPEAT and define a better semantic for it. One thought was to rename it to __GFP_BEST_EFFORT which would behave consistently for all orders and guarantee that the allocation would try as long as it seem feasible or fail eventually. !costly request would then finally get a request context which neiter fails too early (GFP_NORETRY) nor endlessly loops in the allocator for ever (default behavior). Costly high order requests would keep the current semantic. We have discussed that at LSF/MM this year and another suggestion was to introduce __GFP_TRYHARD instead which would be implicit for all orders and users would opt out by ~__GFP_TRYHARD instead. I am not sure which way is better right now but I plan to do the clean up first before going further with semantic changes. $ git grep __GFP_REPEAT next/master | wc -l 109 $ git grep __GFP_REPEAT | wc -l 35 So we are down to the third after this patch series. The remaining places really seem to be relying on __GFP_REPEAT due to large allocation requests. This still needs some double checking which I will do later after all the simple ones are sorted out. I am touching a lot of arch specific code here and I hope I got it right but as a matter of fact I even didn't compile test for some archs as I do not have cross compiler for them. Patches should be quite trivial to review for stupid compile mistakes though. The tricky parts are usually hidden by macro definitions and thats where I would appreciate help from arch maintainers. [1] http://lkml.kernel.org/r/1460372892-8157-1-git-send-email-mhocko@kernel.org