Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752215AbcCKLnu (ORCPT ); Fri, 11 Mar 2016 06:43:50 -0500 Received: from mail-lb0-f173.google.com ([209.85.217.173]:33955 "EHLO mail-lb0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752073AbcCKLnl (ORCPT ); Fri, 11 Mar 2016 06:43:41 -0500 Subject: Re: [PATCH v4 5/7] mm, kasan: Stackdepot implementation. Enable stackdepot for SLAB To: Alexander Potapenko , Steven Rostedt References: <00e9fa7d4adeac2d37a42cf613837e74850d929a.1456504662.git.glider@google.com> <56D471F5.3010202@gmail.com> <56D58398.2010708@gmail.com> Cc: Dmitry Vyukov , Andrey Konovalov , Christoph Lameter , Andrew Morton , Joonsoo Kim , JoonSoo Kim , Kostya Serebryany , kasan-dev , LKML , "linux-mm@kvack.org" From: Andrey Ryabinin Message-ID: <56E2AF71.2050800@gmail.com> Date: Fri, 11 Mar 2016 14:43:45 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2351 Lines: 53 On 03/11/2016 02:18 PM, Alexander Potapenko wrote: > On Thu, Mar 10, 2016 at 5:58 PM, Andrey Ryabinin wrote: >> 2016-03-08 14:42 GMT+03:00 Alexander Potapenko : >>> On Tue, Mar 1, 2016 at 12:57 PM, Andrey Ryabinin wrote: >>>>>> >>>>>>> + page = alloc_pages(alloc_flags, STACK_ALLOC_ORDER); >>>>>> >>>>>> STACK_ALLOC_ORDER = 4 - that's a lot. Do you really need that much? >>>>> >>>>> Part of the issue the atomic context above. When we can't allocate >>>>> memory we still want to save the stack trace. When we have less than >>>>> STACK_ALLOC_ORDER memory, we try to preallocate another >>>>> STACK_ALLOC_ORDER in advance. So in the worst case, we have >>>>> STACK_ALLOC_ORDER memory and that should be enough to handle all >>>>> kmalloc/kfree in the atomic context. 1 page does not look enough. I >>>>> think Alex did some measuring of the failure race (when we are out of >>>>> memory and can't allocate more). >>>>> >>>> >>>> A lot of 4-order pages will lead to high fragmentation. You don't need physically contiguous memory here, >>>> so try to use vmalloc(). It is slower, but fragmentation won't be problem. >>> I've tried using vmalloc(), but turned out it's calling KASAN hooks >>> again. Dealing with reentrancy in this case sounds like an overkill. >> >> We'll have to deal with recursion eventually. Using stackdepot for >> page owner will cause recursion. >> >>> Given that we only require 9 Mb most of the time, is allocating >>> physical pages still a problem? >>> >> >> This is not about size, this about fragmentation. vmalloc allows to >> utilize available low-order pages, >> hence reduce the fragmentation. > I've attempted to add __vmalloc(STACK_ALLOC_SIZE, alloc_flags, > PAGE_KERNEL) (also tried vmalloc(STACK_ALLOC_SIZE)) instead of > page_alloc() and am now getting a crash in > kmem_cache_alloc_node_trace() in mm/slab.c, because it doesn't allow > the kmem_cache pointer to be NULL (it's dereferenced when calling > trace_kmalloc_node()). > > Steven, do you know if this because of my code violating some contract > (e.g. I'm calling vmalloc() too early, when kmalloc_caches[] haven't > been initialized), Probably. kmem_cache_init() goes before vmalloc_init(). > or is this a bug in kmem_cache_alloc_node_trace() > itself? >