Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757454AbcCDHB1 (ORCPT ); Fri, 4 Mar 2016 02:01:27 -0500 Received: from szxga01-in.huawei.com ([58.251.152.64]:46776 "EHLO szxga01-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751227AbcCDHB0 (ORCPT ); Fri, 4 Mar 2016 02:01:26 -0500 Subject: Re: Suspicious error for CMA stress test To: Joonsoo Kim References: <56D6F008.1050600@huawei.com> <56D79284.3030009@redhat.com> <56D832BD.5080305@huawei.com> <20160304020232.GA12036@js1304-P5Q-DELUXE> CC: Laura Abbott , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , Andrew Morton , Sasha Levin , Laura Abbott , qiuxishi , Catalin Marinas , Will Deacon , Arnd Bergmann , "thunder.leizhen@huawei.com" , dingtinahong , , "linux-mm@kvack.org" From: Hanjun Guo Message-ID: <56D9325B.9060709@huawei.com> Date: Fri, 4 Mar 2016 14:59:39 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:38.0) Gecko/20100101 Thunderbird/38.5.1 MIME-Version: 1.0 In-Reply-To: <20160304020232.GA12036@js1304-P5Q-DELUXE> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 8bit X-Originating-IP: [10.177.17.188] X-CFilter-Loop: Reflected X-Mirapoint-Virus-RAPID-Raw: score=unknown(0), refid=str=0001.0A020203.56D932BB.00B9,ss=1,re=0.000,recu=0.000,reip=0.000,cl=1,cld=1,fgs=0, ip=0.0.0.0, so=2013-06-18 04:22:30, dmn=2013-03-21 17:37:32 X-Mirapoint-Loop-Id: ed41f6e7d2a049fd2d64899ea62c1475 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5483 Lines: 152 On 2016/3/4 10:02, Joonsoo Kim wrote: > On Thu, Mar 03, 2016 at 08:49:01PM +0800, Hanjun Guo wrote: >> On 2016/3/3 15:42, Joonsoo Kim wrote: >>> 2016-03-03 10:25 GMT+09:00 Laura Abbott : >>>> (cc -mm and Joonsoo Kim) >>>> >>>> >>>> On 03/02/2016 05:52 AM, Hanjun Guo wrote: >>>>> Hi, >>>>> >>>>> I came across a suspicious error for CMA stress test: >>>>> >>>>> Before the test, I got: >>>>> -bash-4.3# cat /proc/meminfo | grep Cma >>>>> CmaTotal: 204800 kB >>>>> CmaFree: 195044 kB >>>>> >>>>> >>>>> After running the test: >>>>> -bash-4.3# cat /proc/meminfo | grep Cma >>>>> CmaTotal: 204800 kB >>>>> CmaFree: 6602584 kB >>>>> >>>>> So the freed CMA memory is more than total.. >>>>> >>>>> Also the the MemFree is more than mem total: >>>>> >>>>> -bash-4.3# cat /proc/meminfo >>>>> MemTotal: 16342016 kB >>>>> MemFree: 22367268 kB >>>>> MemAvailable: 22370528 kB >> [...] >>>> I played with this a bit and can see the same problem. The sanity >>>> check of CmaFree < CmaTotal generally triggers in >>>> __move_zone_freepage_state in unset_migratetype_isolate. >>>> This also seems to be present as far back as v4.0 which was the >>>> first version to have the updated accounting from Joonsoo. >>>> Were there known limitations with the new freepage accounting, >>>> Joonsoo? >>> I don't know. I also played with this and looks like there is >>> accounting problem, however, for my case, number of free page is slightly less >>> than total. I will take a look. >>> >>> Hanjun, could you tell me your malloc_size? I tested with 1 and it doesn't >>> look like your case. >> I tested with malloc_size with 2M, and it grows much bigger than 1M, also I >> did some other test: > Thanks! Now, I can re-generate erronous situation you mentioned. > >> - run with single thread with 100000 times, everything is fine. >> >> - I hack the cam_alloc() and free as below [1] to see if it's lock issue, with >> the same test with 100 multi-thread, then I got: > [1] would not be sufficient to close this race. > > Try following things [A]. And, for more accurate test, I changed code a bit more > to prevent kernel page allocation from cma area [B]. This will prevent kernel > page allocation from cma area completely so we can focus cma_alloc/release race. > > Although, this is not correct fix, it could help that we can guess > where the problem is. > > Thanks. > > [A] > diff --git a/mm/cma.c b/mm/cma.c > index c003274..43ed02d 100644 > --- a/mm/cma.c > +++ b/mm/cma.c > @@ -496,7 +496,9 @@ bool cma_release(struct cma *cma, const struct page *pages, unsigned int count) > > VM_BUG_ON(pfn + count > cma->base_pfn + cma->count); > > + mutex_lock(&cma_mutex); > free_contig_range(pfn, count); > + mutex_unlock(&cma_mutex); > cma_clear_bitmap(cma, pfn, count); > trace_cma_release(pfn, pages, count); > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index c6c38ed..1ce8a59 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -2192,7 +2192,8 @@ void free_hot_cold_page(struct page *page, bool cold) > * excessively into the page allocator > */ > if (migratetype >= MIGRATE_PCPTYPES) { > - if (unlikely(is_migrate_isolate(migratetype))) { > + if (is_migrate_cma(migratetype) || > + unlikely(is_migrate_isolate(migratetype))) { > free_one_page(zone, page, pfn, 0, migratetype); > goto out; > } As I replied in previous email, the solution will fix the problem, the Cma freed memory and system freed memory is in sane state after apply above patch. I also tested this situation which only apply the code below: if (migratetype >= MIGRATE_PCPTYPES) { - if (unlikely(is_migrate_isolate(migratetype))) { + if (is_migrate_cma(migratetype) || + unlikely(is_migrate_isolate(migratetype))) { free_one_page(zone, page, pfn, 0, migratetype); goto out; } This will not fix the problem, but will reduce the errorous freed number of memory, hope this helps. > > > [B] > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index f2dccf9..c6c38ed 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -1493,6 +1493,7 @@ static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags, > int alloc_flags) > { > int i; > + bool cma = false; > > for (i = 0; i < (1 << order); i++) { > struct page *p = page + i; > @@ -1500,6 +1501,9 @@ static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags, > return 1; > } > > + if (is_migrate_cma(get_pcppage_migratetype(page))) > + cma = true; > + > set_page_private(page, 0); > set_page_refcounted(page); > > @@ -1528,6 +1532,12 @@ static int prep_new_page(struct page *page, unsigned int order, gfp_t gfp_flags, > else > clear_page_pfmemalloc(page); > > + if (cma) { > + page_ref_dec(page); mm/page_alloc.c: In function ?prep_new_page?: mm/page_alloc.c:1407:3: error: implicit declaration of function ?page_ref_dec? [-Werror=implicit-function-declaration] page_ref_dec(page); ^ Typo? Thanks Hanjun