From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx2.suse.de ([195.135.220.15]:50316 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726393AbeK3MQ6 (ORCPT ); Fri, 30 Nov 2018 07:16:58 -0500 From: NeilBrown To: Al Viro Date: Fri, 30 Nov 2018 12:09:20 +1100 Cc: Andrew Morton , Linus Torvalds , paulmck@linux.vnet.ibm.com, Florian Weimer , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Josh Triplett Subject: Re: [PATCH - resend*2] VFS: use synchronize_rcu_expedited() in namespace_unlock() In-Reply-To: <20181129235222.GJ2217@ZenIV.linux.org.uk> References: <87y3nyd4pu.fsf@notabene.neil.brown.name> <20171026122743.GX3659@linux.vnet.ibm.com> <20171127144125.GF3624@linux.vnet.ibm.com> <87induxd3u.fsf@notabene.neil.brown.name> <87tvm1rxme.fsf@notabene.neil.brown.name> <20181005014002.GS32577@ZenIV.linux.org.uk> <87mupro3wh.fsf@notabene.neil.brown.name> <20181129235222.GJ2217@ZenIV.linux.org.uk> Message-ID: <87k1kvnzgf.fsf@notabene.neil.brown.name> MIME-Version: 1.0 Content-Type: multipart/signed; boundary="=-=-="; micalg=pgp-sha256; protocol="application/pgp-signature" Sender: linux-fsdevel-owner@vger.kernel.org List-ID: --=-=-= Content-Type: text/plain Content-Transfer-Encoding: quoted-printable On Thu, Nov 29 2018, Al Viro wrote: > On Fri, Nov 30, 2018 at 10:33:18AM +1100, NeilBrown wrote: >>=20 >> The synchronize_rcu() in namespace_unlock() is called every time >> a filesystem is unmounted. If a great many filesystems are mounted, >> this can cause a noticable slow-down in, for example, system shutdown. >>=20 >> The sequence: >> mkdir -p /tmp/Mtest/{0..5000} >> time for i in /tmp/Mtest/*; do mount -t tmpfs tmpfs $i ; done >> time umount /tmp/Mtest/* >>=20 >> on a 4-cpu VM can report 8 seconds to mount the tmpfs filesystems, and >> 100 seconds to unmount them. >>=20 >> Boot the same VM with 1 CPU and it takes 18 seconds to mount the >> tmpfs filesystems, but only 36 to unmount. >>=20 >> If we change the synchronize_rcu() to synchronize_rcu_expedited() >> the umount time on a 4-cpu VM drop to 0.6 seconds >>=20 >> I think this 200-fold speed up is worth the slightly high system >> impact of using synchronize_rcu_expedited(). >>=20 >> Acked-by: Paul E. McKenney (from general rc= u perspective) >> Signed-off-by: NeilBrown >> --- >>=20 >> Al Viro says "I can live with this one" but this still hasn't landed. >> Maybe someone else could apply it? > > Applied (in work.misc, once I push it out) Excellent - thanks a lot :-) NeilBrown --=-=-= Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEEG8Yp69OQ2HB7X0l6Oeye3VZigbkFAlwAjcEACgkQOeye3VZi gbko4g//XLXF+VP16o6Qh5aV6rw8fHBklFGwVnI0Xp6w64oyxDqsdt+he9D40zYO pek2Q/Brwaqjbrs1NE0YfJ2ZmH4PLQTGI3xWBLW7Bx7EnUvEpbFap2gM9E7efLz3 U0ZSgI/m795vesaRW5GV0xJOEHL/I7fpZsY78lg+p7vwQmvG9AKHzxFXDdXHu5bn DcjLm47i2fykdyt/5SbmoeWKgMIiQimfgRUFgO/fvbRsiFmjUx+zCHxzkGeixFfn 8UyvE7zxDAQAEGKVJ1JwrfikUlLm9TssEhzRgYdtqaWaA80IjpDXSG/O856K1F2Q O5auYawp3D/+J+ZXC/pEsYuqwUp//sWeDQ3IoNbqqWg/+lufto/5dROLg9jdp6o9 vInPbZzVgtFJzYXxJY0ybf0CiQAz2yuID098Gydx5RTHV+GMx6XPBbYmkdOn0MsS CMKan+a7D8wQfnmvCK8XiiZWQjx45yw2oPpr9mdpDME2fXAPpngFCL4GEAgYVNrL RiT9MzjbanVM0VznjSbpIeyvv2loLCwhdUmK6mD+ECmEWZ4FgVpman8G/1CTczHV x3Kw9tANoZjd0jXJhqdlJuE9BKwZ4kHUgTQSgGCYrIy7UIo1RWNHZq6gMiVtTFm8 zCU1VputwDWbJtFtP7xc8f2jIyanselRT9cK+KcZfqw/U4z00vM= =McWo -----END PGP SIGNATURE----- --=-=-=--