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Date: Thu, 22 May 2014 16:01:20 +0300 From: Marian Marinov <mm@...com> To: Manfred Spraul <manfred@...orfullife.com>, Davidlohr Bueso <davidlohr@...com> CC: akpm@...ux-foundation.org, n-horiguchi@...jp.nec.com, Greg KH <gregkh@...uxfoundation.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Linux Containers <containers@...ts.linux-foundation.org> Subject: Re: [PATCH] IPC initialize shmmax and shmall from the current value not the default -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On 05/05/2014 10:59 PM, Marian Marinov wrote: > On 05/04/2014 02:17 PM, Manfred Spraul wrote: >> Hi Marian, >> >> Note: The limits will soon be increased to (nearly) ULONG_MAX. I.e.: If you propose the patch because you are >> running into issues with a too small SEMMAX after an unshare(CLONE_NEWIPC), then this will be fixed soon. >> >> >> On 05/04/2014 01:53 AM, Davidlohr Bueso wrote: >>> On Sun, 2014-05-04 at 01:48 +0300, Marian Marinov wrote: >>>> When we are creating new IPC namespace that should be cloned from the current namespace it is a good idea to >>>> copy the values of the current shmmax and shmall to the new namespace. >> The idea sounds reasonable: If an admin has reduced the limits, then the reduction should also apply after a >> unshare(CLONE_NEWIPC). >> >> But: Your patch doesn't use the current shmmax, it uses the shmmax from init_ipc_ns. Would it be possible to use >> the current values? > > In my tests it worked exactly as expected. Here is an example: > > [root@sp2 ~]# sysctl -a|grep shmmax kernel.shmmax = 68719476736 [root@sp2 ~]# lxc-attach -n cent_plain > [root@...alhost ~]# sysctl -a|grep shmmax kernel.shmmax = 68719476736 [root@...alhost ~]# halt [root@sp2 ~]# sysctl > -a|grep shmmax kernel.shmmax = 68719476736 [root@sp2 ~]# sysctl kernel.shmmax=34359738368 kernel.shmmax = > 34359738368 [root@sp2 ~]# lxc-start -n cent_plain -d [root@sp2 ~]# lxc-attach -n cent_plain [root@...alhost ~]# > sysctl -a|grep shmmax kernel.shmmax = 34359738368 [root@...alhost ~]# > > So it seams to work as expected :) > > It works because wen you setup a new shmmax limit it is actually the limit in the init_ipc_ns. So when we are > creating a new ipc_ns its ok to copy the values from init_ipc_ns. > > -Marian > Ping? So will there be any more comments on that? Marian >> >>> Why is this a good idea? >>> >>> This would break userspace that relies on the current behavior. Furthermore we've recently changed the default >>> value of both these limits to be as large as you can get, thus deprecating them. I don't like the idea of this >>> being replaced by namespaces. >> Davidlohr: We are not deprecating them, we make the default huge. The limits should stay as usable as they were. >> >> With regards to breaking user space, I must think about it a bit more. Right now, each new namespace starts with >> SEMMAX=32MB, i.e. an often unusable default. >> >> -- Manfred >> > > - -- Marian Marinov Founder & CEO of 1H Ltd. Jabber/GTalk: hackman@...ber.org ICQ: 7556201 Mobile: +359 886 660 270 -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.22 (GNU/Linux) iEYEARECAAYFAlN99SAACgkQ4mt9JeIbjJQHrQCfdexU5xdW4A/pO66SvbcYQVqF uREAoJ1e6hytp6435YUrpKjEG2qVulI1 =QqGi -----END PGP SIGNATURE----- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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