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[23.128.96.18]) by mx.google.com with ESMTP id t11si145857eju.257.2020.05.13.00.17.43; Wed, 13 May 2020 00:18:06 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-nfs-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; spf=pass (google.com: domain of linux-nfs-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-nfs-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728490AbgEMHRc (ORCPT + 99 others); Wed, 13 May 2020 03:17:32 -0400 Received: from mx2.suse.de ([195.135.220.15]:60738 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726020AbgEMHRb (ORCPT ); Wed, 13 May 2020 03:17:31 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 43165B1E7; Wed, 13 May 2020 07:17:31 +0000 (UTC) From: NeilBrown To: Jan Kara Date: Wed, 13 May 2020 17:17:20 +1000 Cc: Andrew Morton , Michal Hocko , linux-mm@kvack.org, linux-nfs@vger.kernel.org, LKML , Christoph Hellwig Subject: [PATCH 1/2 V4] MM: replace PF_LESS_THROTTLE with PF_LOCAL_THROTTLE In-Reply-To: <871rnob8z3.fsf@notabene.neil.brown.name> References: <87tv2b7q72.fsf@notabene.neil.brown.name> <87v9miydai.fsf@notabene.neil.brown.name> <87ftdgw58w.fsf@notabene.neil.brown.name> <87wo6gs26e.fsf@notabene.neil.brown.name> <87tv1ks24t.fsf@notabene.neil.brown.name> <20200416151906.GQ23739@quack2.suse.cz> <87zhb5r30c.fsf@notabene.neil.brown.name> <20200422124600.GH8775@quack2.suse.cz> <871rnob8z3.fsf@notabene.neil.brown.name> Message-ID: <87y2pw9udb.fsf@notabene.neil.brown.name> MIME-Version: 1.0 Content-Type: multipart/signed; boundary="=-=-="; micalg=pgp-sha256; protocol="application/pgp-signature" Sender: linux-nfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-nfs@vger.kernel.org --=-=-= Content-Type: text/plain Content-Transfer-Encoding: quoted-printable PF_LESS_THROTTLE exists for loop-back nfsd (and a similar need in the loop block driver and callers of prctl(PR_SET_IO_FLUSHER)), where a daemon needs to write to one bdi (the final bdi) in order to free up writes queued to another bdi (the client bdi). The daemon sets PF_LESS_THROTTLE and gets a larger allowance of dirty pages, so that it can still dirty pages after other processses have been throttled. The purpose of this is to avoid deadlock that happen when the PF_LESS_THROTTLE process must write for any dirty pages to be freed, but it is being thottled and cannot write. This approach was designed when all threads were blocked equally, independently on which device they were writing to, or how fast it was. Since that time the writeback algorithm has changed substantially with different threads getting different allowances based on non-trivial heuristics. This means the simple "add 25%" heuristic is no longer reliable. The important issue is not that the daemon needs a *larger* dirty page allowance, but that it needs a *private* dirty page allowance, so that dirty pages for the "client" bdi that it is helping to clear (the bdi for an NFS filesystem or loop block device etc) do not affect the throttling of the deamon writing to the "final" bdi. This patch changes the heuristic so that the task is not throttled when the bdi it is writing to has a dirty page count below below (or equal to) the free-run threshold for that bdi. This ensures it will always be able to have some pages in flight, and so will not deadlock. In a steady-state, it is expected that PF_LOCAL_THROTTLE tasks might still be throttled by global threshold, but that is acceptable as it is only the deadlock state that is interesting for this flag. This approach of "only throttle when target bdi is busy" is consistent with the other use of PF_LESS_THROTTLE in current_may_throttle(), were it causes attention to be focussed only on the target bdi. So this patch - renames PF_LESS_THROTTLE to PF_LOCAL_THROTTLE, - removes the 25% bonus that that flag gives, and - If PF_LOCAL_THROTTLE is set, don't delay at all unless the global and the local free-run thresholds are exceeded. Note that previously realtime threads were treated the same as PF_LESS_THROTTLE threads. This patch does *not* change the behvaiour for real-time threads, so it is now different from the behaviour of nfsd and loop tasks. I don't know what is wanted for realtime. Acked-by: Chuck Lever (for nfsd change) Signed-off-by: NeilBrown =2D-- drivers/block/loop.c | 2 +- fs/nfsd/vfs.c | 9 +++++---- include/linux/sched.h | 3 ++- kernel/sys.c | 2 +- mm/page-writeback.c | 41 +++++++++++++++++++++++++++++++++-------- mm/vmscan.c | 4 ++-- 6 files changed, 44 insertions(+), 17 deletions(-) diff --git a/drivers/block/loop.c b/drivers/block/loop.c index da693e6a834e..d89c25ba3b89 100644 =2D-- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -919,7 +919,7 @@ static void loop_unprepare_queue(struct loop_device *lo) =20 static int loop_kthread_worker_fn(void *worker_ptr) { =2D current->flags |=3D PF_LESS_THROTTLE | PF_MEMALLOC_NOIO; + current->flags |=3D PF_LOCAL_THROTTLE | PF_MEMALLOC_NOIO; return kthread_worker_fn(worker_ptr); } =20 diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c index 0aa02eb18bd3..c3fbab1753ec 100644 =2D-- a/fs/nfsd/vfs.c +++ b/fs/nfsd/vfs.c @@ -979,12 +979,13 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh = *fhp, struct nfsd_file *nf, =20 if (test_bit(RQ_LOCAL, &rqstp->rq_flags)) /* =2D * We want less throttling in balance_dirty_pages() =2D * and shrink_inactive_list() so that nfs to + * We want throttling in balance_dirty_pages() + * and shrink_inactive_list() to only consider + * the backingdev we are writing to, so that nfs to * localhost doesn't cause nfsd to lock up due to all * the client's dirty pages or its congested queue. */ =2D current->flags |=3D PF_LESS_THROTTLE; + current->flags |=3D PF_LOCAL_THROTTLE; =20 exp =3D fhp->fh_export; use_wgather =3D (rqstp->rq_vers =3D=3D 2) && EX_WGATHER(exp); @@ -1037,7 +1038,7 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh = *fhp, struct nfsd_file *nf, nfserr =3D nfserrno(host_err); } if (test_bit(RQ_LOCAL, &rqstp->rq_flags)) =2D current_restore_flags(pflags, PF_LESS_THROTTLE); + current_restore_flags(pflags, PF_LOCAL_THROTTLE); return nfserr; } =20 diff --git a/include/linux/sched.h b/include/linux/sched.h index 4418f5cb8324..5955a089df32 100644 =2D-- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1481,7 +1481,8 @@ extern struct pid *cad_pid; #define PF_KSWAPD 0x00020000 /* I am kswapd */ #define PF_MEMALLOC_NOFS 0x00040000 /* All allocation requests will inheri= t GFP_NOFS */ #define PF_MEMALLOC_NOIO 0x00080000 /* All allocation requests will inheri= t GFP_NOIO */ =2D#define PF_LESS_THROTTLE 0x00100000 /* Throttle me less: I clean memory = */ +#define PF_LOCAL_THROTTLE 0x00100000 /* Throttle writes only agasint the b= di I write to, + * I am cleaning dirty pages from some other bdi. */ #define PF_KTHREAD 0x00200000 /* I am a kernel thread */ #define PF_RANDOMIZE 0x00400000 /* Randomize virtual address space */ #define PF_SWAPWRITE 0x00800000 /* Allowed to write to swap */ diff --git a/kernel/sys.c b/kernel/sys.c index d325f3ab624a..180a2fa33f7f 100644 =2D-- a/kernel/sys.c +++ b/kernel/sys.c @@ -2262,7 +2262,7 @@ int __weak arch_prctl_spec_ctrl_set(struct task_struc= t *t, unsigned long which, return -EINVAL; } =20 =2D#define PR_IO_FLUSHER (PF_MEMALLOC_NOIO | PF_LESS_THROTTLE) +#define PR_IO_FLUSHER (PF_MEMALLOC_NOIO | PF_LOCAL_THROTTLE) =20 SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, ar= g3, unsigned long, arg4, unsigned long, arg5) diff --git a/mm/page-writeback.c b/mm/page-writeback.c index 7326b54ab728..f02a71797781 100644 =2D-- a/mm/page-writeback.c +++ b/mm/page-writeback.c @@ -387,8 +387,7 @@ static unsigned long global_dirtyable_memory(void) * Calculate @dtc->thresh and ->bg_thresh considering * vm_dirty_{bytes|ratio} and dirty_background_{bytes|ratio}. The caller * must ensure that @dtc->avail is set before calling this function. The =2D * dirty limits will be lifted by 1/4 for PF_LESS_THROTTLE (ie. nfsd) and =2D * real-time tasks. + * dirty limits will be lifted by 1/4 for real-time tasks. */ static void domain_dirty_limits(struct dirty_throttle_control *dtc) { @@ -436,7 +435,7 @@ static void domain_dirty_limits(struct dirty_throttle_c= ontrol *dtc) if (bg_thresh >=3D thresh) bg_thresh =3D thresh / 2; tsk =3D current; =2D if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) { + if (rt_task(tsk)) { bg_thresh +=3D bg_thresh / 4 + global_wb_domain.dirty_limit / 32; thresh +=3D thresh / 4 + global_wb_domain.dirty_limit / 32; } @@ -486,7 +485,7 @@ static unsigned long node_dirty_limit(struct pglist_dat= a *pgdat) else dirty =3D vm_dirty_ratio * node_memory / 100; =20 =2D if (tsk->flags & PF_LESS_THROTTLE || rt_task(tsk)) + if (rt_task(tsk)) dirty +=3D dirty / 4; =20 return dirty; @@ -1653,8 +1652,12 @@ static void balance_dirty_pages(struct bdi_writeback= *wb, if (dirty <=3D dirty_freerun_ceiling(thresh, bg_thresh) && (!mdtc || m_dirty <=3D dirty_freerun_ceiling(m_thresh, m_bg_thresh))) { =2D unsigned long intv =3D dirty_poll_interval(dirty, thresh); =2D unsigned long m_intv =3D ULONG_MAX; + unsigned long intv; + unsigned long m_intv; + + free_running: + intv =3D dirty_poll_interval(dirty, thresh); + m_intv =3D ULONG_MAX; =20 current->dirty_paused_when =3D now; current->nr_dirtied =3D 0; @@ -1673,9 +1676,20 @@ static void balance_dirty_pages(struct bdi_writeback= *wb, * Calculate global domain's pos_ratio and select the * global dtc by default. */ =2D if (!strictlimit) + if (!strictlimit) { wb_dirty_limits(gdtc); =20 + if ((current->flags & PF_LOCAL_THROTTLE) && + gdtc->wb_dirty < + dirty_freerun_ceiling(gdtc->wb_thresh, + gdtc->wb_bg_thresh)) + /* + * LOCAL_THROTTLE tasks must not be throttled + * when below the per-wb freerun ceiling. + */ + goto free_running; + } + dirty_exceeded =3D (gdtc->wb_dirty > gdtc->wb_thresh) && ((gdtc->dirty > gdtc->thresh) || strictlimit); =20 @@ -1689,9 +1703,20 @@ static void balance_dirty_pages(struct bdi_writeback= *wb, * both global and memcg domains. Choose the one * w/ lower pos_ratio. */ =2D if (!strictlimit) + if (!strictlimit) { wb_dirty_limits(mdtc); =20 + if ((current->flags & PF_LOCAL_THROTTLE) && + mdtc->wb_dirty < + dirty_freerun_ceiling(mdtc->wb_thresh, + mdtc->wb_bg_thresh)) + /* + * LOCAL_THROTTLE tasks must not be + * throttled when below the per-wb + * freerun ceiling. + */ + goto free_running; + } dirty_exceeded |=3D (mdtc->wb_dirty > mdtc->wb_thresh) && ((mdtc->dirty > mdtc->thresh) || strictlimit); =20 diff --git a/mm/vmscan.c b/mm/vmscan.c index a37c87b5aee2..b2f5deb3603c 100644 =2D-- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1878,13 +1878,13 @@ static unsigned noinline_for_stack move_pages_to_lr= u(struct lruvec *lruvec, =20 /* * If a kernel thread (such as nfsd for loop-back mounts) services =2D * a backing device by writing to the page cache it sets PF_LESS_THROTTL= E. + * a backing device by writing to the page cache it sets PF_LOCAL_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) { =2D return !(current->flags & PF_LESS_THROTTLE) || + return !(current->flags & PF_LOCAL_THROTTLE) || current->backing_dev_info =3D=3D NULL || bdi_write_congested(current->backing_dev_info); } =2D-=20 2.26.2 --=-=-= Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEEG8Yp69OQ2HB7X0l6Oeye3VZigbkFAl67nwEACgkQOeye3VZi gbl0EhAAo61GC9pWh+if1TLGzsiyMiMEUeFZ0Wm6khcyc5A+qbfVIUvhffZpqwpR TFwL0HTAj1jKE7WMWVEZ27Oaq5Mxi88IskYWh45SeeLt8+L0i7YFHU4KICNL2piQ 0VIdKCts0ScxbwOAN16Pm1ydnHLWpNhBGIwI78/hT2pfLURiy1tcKYkPlRPtCuv5 meYOsFZwMdrFB2lgRKnmHOAunmPx6ftLMFlQxd2eEou0O8oRF6R0RjpppgWMY0o8 JWhQHaW/uYk+jC4z05CKYeJxxQ9QN0iS0XDQmDRywVIBlsw1Md4F1utsME4HaRxO tEaejVtjlKtJB3HMATyyMrFhVs8cjWChNtlpq2H/2FLu1/FsazUUm0HmUeLq7g0J 1k3wr/p/abc17Ngxv2EnGPrdp5hLuxXR4dnbG6YmKBxor8iSl2Hc43YHpaMalSNX RQjo/eVFXn+j7F9NeRgLaMYC3a1Pvydj+HcgVmJ1hOlrrqzRrURYl3A2zH0RsIri BChtJiCrh0fvo3dL0YZuS1uh4e4TBEJny+SEDF43He5DW/kkIhDj2zwCc1bM52Vm ldQN6v1lFLd5GtKLl78siQ/OfW44FQA3RU1cQg/ruwJVe6Pcv03ekur/lP4cRdmi YNNjCiRCEQiO2NUu81S77FpvtcG6dj6ciNIyc1j2lZ5l5mh2OC0= =C/9S -----END PGP SIGNATURE----- --=-=-=--