Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752102AbaDWWtZ (ORCPT ); Wed, 23 Apr 2014 18:49:25 -0400 Received: from cantor2.suse.de ([195.135.220.15]:42831 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751545AbaDWWtY (ORCPT ); Wed, 23 Apr 2014 18:49:24 -0400 Date: Thu, 24 Apr 2014 08:49:16 +1000 From: NeilBrown To: Andrew Morton Cc: linux-mm@kvack.org, lkml Subject: [PATCH revised - was 1/5] MM: avoid throttling reclaim for loop-back nfsd threads. Message-ID: <20140424084916.2f1da0c8@notabene.brown> X-Mailer: Claws Mail 3.9.2 (GTK+ 2.24.22; x86_64-suse-linux-gnu) Mime-Version: 1.0 Content-Type: multipart/signed; micalg=PGP-SHA1; boundary="Sig_/ZslvOujvpOu=TtTjOBITTty"; protocol="application/pgp-signature" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --Sig_/ZslvOujvpOu=TtTjOBITTty Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable When a loop-back NFS mount is active and the backing device for the NFS mount becomes congested, that can impose throttling delays on the nfsd threads. These delays significantly reduce throughput and so the NFS mount remains congested. This results in a live lock and the reduced throughput persists. This live lock has been found in testing with the 'wait_iff_congested' call, and could possibly be caused by the 'congestion_wait' call. This livelock is similar to the deadlock which justified the introduction of PF_LESS_THROTTLE, and the same flag can be used to remove this livelock. To minimise the impact of the change, we still throttle nfsd when the filesystem it is writing to is congested, but not when some separate filesystem (e.g. the NFS filesystem) is congested. Signed-off-by: NeilBrown diff --git a/mm/vmscan.c b/mm/vmscan.c index a9c74b409681..ce0e4dfc6d67 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1425,6 +1425,19 @@ putback_inactive_pages(struct lruvec *lruvec, struct= list_head *page_list) } =20 /* + * If a kernel thread (such as nfsd for loop-back mounts) services + * a backing device by writing to the page cache it sets PF_LESS_THROTTLE. + * In that case we should only throttle if the backing device it is + * writing to is congested. In other cases it is safe to throttle. + */ +static int current_may_throttle(void) +{ + return !(current->flags & PF_LESS_THROTTLE) || + current->backing_dev_info =3D=3D NULL || + bdi_write_congested(current->backing_dev_info); +} + +/* * shrink_inactive_list() is a helper for shrink_zone(). It returns the n= umber * of reclaimed pages */ @@ -1552,7 +1565,8 @@ shrink_inactive_list(unsigned long nr_to_scan, struct= lruvec *lruvec, * implies that pages are cycling through the LRU faster than * they are written so also forcibly stall. */ - if (nr_unqueued_dirty =3D=3D nr_taken || nr_immediate) + if ((nr_unqueued_dirty =3D=3D nr_taken || nr_immediate) && + current_may_throttle()) congestion_wait(BLK_RW_ASYNC, HZ/10); } =20 @@ -1561,7 +1575,8 @@ shrink_inactive_list(unsigned long nr_to_scan, struct= lruvec *lruvec, * is congested. Allow kswapd to continue until it starts encountering * unqueued dirty pages or cycling through the LRU too quickly. */ - if (!sc->hibernation_mode && !current_is_kswapd()) + if (!sc->hibernation_mode && !current_is_kswapd() && + current_may_throttle()) wait_iff_congested(zone, BLK_RW_ASYNC, HZ/10); =20 trace_mm_vmscan_lru_shrink_inactive(zone->zone_pgdat->node_id, --Sig_/ZslvOujvpOu=TtTjOBITTty Content-Type: application/pgp-signature; name=signature.asc Content-Disposition: attachment; filename=signature.asc -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.22 (GNU/Linux) iQIVAwUBU1hDbDnsnt1WYoG5AQKczg//VjNRwC4g736Gt3Ec1HcynbycVjUzybHW yrFn67CeL0HK/J5bQX5Jw4Lvuws0EeRrfRyOnFScw5kIIfFiU6qSOtQEj09BVD58 ZUFN4PdaMqd2YjLf/hzfJcw198kSm75CvYo8ZlsgSot0eDQmdCkaLsfPY4DJO2zP 160qvrfMcSihq/e8V/pmmMkF+VfsiMhNx7+bNwjH9JinSl1UjWTt0j86paENuIIQ ubS/Xik2r8+MvK5LDQnSWYMhis+hiDPceELoykuTasOOxifdXw1SvRvp25N284xM q9sYP8XHVB4swQzEuQVxw8l4Htm9Yl3TOYw6yUWNDoSvNX/eTelcP78nB8UaBxZy ffBB/8snO7kelT1qGEmTWZva/jPCNWjeNYJrRjLBzPd9DVgl/zqZNKkpl/n/1yNX KeHXX2GBxh12B1uYAcvUT/7sGk954uHGIX9lK+DWhXWEwUTCAqMxpfKBNVrM5eWG PI/to5cWBN82V28tLVf3YzxlKlsJ8rDEyiNnOyR8xpKXRmF8a6Ol6zSTwIi/fRTm Xv/I3awk9PCGaezyv/cmbGkFbE3/BGxE7HTC4C4CEf0LJ7IxZFJs0drxu++3YNkT DoPWivg2YBB8XxFm7U1usGWHnmqF48oWj4yUn6rkuA1/ob/398kc1L2GPUXeE0gW 2uerYmLgsPY= =Fo/n -----END PGP SIGNATURE----- --Sig_/ZslvOujvpOu=TtTjOBITTty-- -- 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/