Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752184AbaDCOI3 (ORCPT ); Thu, 3 Apr 2014 10:08:29 -0400 Received: from fgwmail5.fujitsu.co.jp ([192.51.44.35]:43928 "EHLO fgwmail5.fujitsu.co.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752131AbaDCOI2 (ORCPT ); Thu, 3 Apr 2014 10:08:28 -0400 X-SecurityPolicyCheck: OK by SHieldMailChecker v1.8.4 Message-ID: <533D6B28.6070305@jp.fujitsu.com> Date: Thu, 03 Apr 2014 23:07:36 +0900 From: Kamezawa Hiroyuki User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:24.0) Gecko/20100101 Thunderbird/24.4.0 MIME-Version: 1.0 To: Davidlohr Bueso , KOSAKI Motohiro CC: Andrew Morton , Manfred Spraul , aswin@hp.com, LKML , "linux-mm@kvack.org" , Greg Thelen Subject: Re: [PATCH] ipc,shm: disable shmmax and shmall by default References: <1396235199.2507.2.camel@buesod1.americas.hpqcorp.net> <20140331170546.3b3e72f0.akpm@linux-foundation.org> <1396371699.25314.11.camel@buesod1.americas.hpqcorp.net> <1396377083.25314.17.camel@buesod1.americas.hpqcorp.net> <1396386062.25314.24.camel@buesod1.americas.hpqcorp.net> <20140401142947.927642a408d84df27d581e36@linux-foundation.org> <20140401144801.603c288674ab8f417b42a043@linux-foundation.org> <1396394931.25314.34.camel@buesod1.americas.hpqcorp.net> <1396484447.2953.1.camel@buesod1.americas.hpqcorp.net> In-Reply-To: <1396484447.2953.1.camel@buesod1.americas.hpqcorp.net> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org (2014/04/03 9:20), Davidlohr Bueso wrote: > The default size for shmmax is, and always has been, 32Mb. > Today, in the XXI century, it seems that this value is rather small, > making users have to increase it via sysctl, which can cause > unnecessary work and userspace application workarounds[1]. > > Instead of choosing yet another arbitrary value, larger than 32Mb, > this patch disables the use of both shmmax and shmall by default, > allowing users to create segments of unlimited sizes. Users and > applications that already explicitly set these values through sysctl > are left untouched, and thus does not change any of the behavior. > > So a value of 0 bytes or pages, for shmmax and shmall, respectively, > implies unlimited memory, as opposed to disabling sysv shared memory. > This is safe as 0 cannot possibly be used previously as SHMMIN is > hardcoded to 1 and cannot be modified. > > This change allows Linux to treat shm just as regular anonymous memory. > One important difference between them, though, is handling out-of-memory > conditions: as opposed to regular anon memory, the OOM killer will not > kill processes that are hogging memory through shm, allowing users to > potentially abuse this. To overcome this situation, the shm_rmid_forced > option must be enabled. > > Running this patch through LTP, everything passes, except the following, > which, due to the nature of this change, is quite expected: > > shmget02 1 TFAIL : call succeeded unexpectedly > > [1]: http://rhaas.blogspot.com/2012/06/absurd-shared-memory-limits.html > > Signed-off-by: Davidlohr Bueso looks good to me Acked-by: KAMEZAWA Hiroyuki When this goes mainline, updating a man page of ipcs may be required. Thanks, -Kame > --- > include/linux/shm.h | 2 +- > include/uapi/linux/shm.h | 8 ++++---- > ipc/shm.c | 6 ++++-- > 3 files changed, 9 insertions(+), 7 deletions(-) > > diff --git a/include/linux/shm.h b/include/linux/shm.h > index 1e2cd2e..0ca06a3 100644 > --- a/include/linux/shm.h > +++ b/include/linux/shm.h > @@ -4,7 +4,7 @@ > #include > #include > > -#define SHMALL (SHMMAX/PAGE_SIZE*(SHMMNI/16)) /* max shm system wide (pages) */ > +#define SHMALL 0 /* max shm system wide (pages) */ > #include > struct shmid_kernel /* private to the kernel */ > { > diff --git a/include/uapi/linux/shm.h b/include/uapi/linux/shm.h > index 78b6941..5f0ef28 100644 > --- a/include/uapi/linux/shm.h > +++ b/include/uapi/linux/shm.h > @@ -9,14 +9,14 @@ > > /* > * SHMMAX, SHMMNI and SHMALL are upper limits are defaults which can > - * be increased by sysctl > + * be increased by sysctl. By default, disable SHMMAX and SHMALL with > + * 0 bytes, thus allowing processes to have unlimited shared memory. > */ > - > -#define SHMMAX 0x2000000 /* max shared seg size (bytes) */ > +#define SHMMAX 0 /* max shared seg size (bytes) */ > #define SHMMIN 1 /* min shared seg size (bytes) */ > #define SHMMNI 4096 /* max num of segs system wide */ > #ifndef __KERNEL__ > -#define SHMALL (SHMMAX/getpagesize()*(SHMMNI/16)) > +#define SHMALL 0 > #endif > #define SHMSEG SHMMNI /* max shared segs per process */ > > diff --git a/ipc/shm.c b/ipc/shm.c > index 7645961..ae01ffa 100644 > --- a/ipc/shm.c > +++ b/ipc/shm.c > @@ -490,10 +490,12 @@ static int newseg(struct ipc_namespace *ns, struct ipc_params *params) > int id; > vm_flags_t acctflag = 0; > > - if (size < SHMMIN || size > ns->shm_ctlmax) > + if (ns->shm_ctlmax && > + (size < SHMMIN || size > ns->shm_ctlmax)) > return -EINVAL; > > - if (ns->shm_tot + numpages > ns->shm_ctlall) > + if (ns->shm_ctlall && > + ns->shm_tot + numpages > ns->shm_ctlall) > return -ENOSPC; > > shp = ipc_rcu_alloc(sizeof(*shp)); > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/