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[209.132.180.67]) by mx.google.com with ESMTP id 109si517112otv.36.2020.04.06.16.43.38; Mon, 06 Apr 2020 16:43:50 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-nfs-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-nfs-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-nfs-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726254AbgDFXnf (ORCPT + 99 others); Mon, 6 Apr 2020 19:43:35 -0400 Received: from mx2.suse.de ([195.135.220.15]:41452 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725933AbgDFXnf (ORCPT ); Mon, 6 Apr 2020 19:43:35 -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 B710FADCE; Mon, 6 Apr 2020 23:43:31 +0000 (UTC) From: NeilBrown To: Trond Myklebust , "Anna.Schumaker\@Netapp.com" , Andrew Morton , Jan Kara , Michal Hocko Date: Tue, 07 Apr 2020 09:43:25 +1000 Cc: linux-mm@kvack.org, linux-nfs@vger.kernel.org, LKML Subject: [PATCH 1/2] MM: replace PF_LESS_THROTTLE with PF_LOCAL_THROTTLE In-Reply-To: <87ftdgw58w.fsf@notabene.neil.brown.name> References: <87tv2b7q72.fsf@notabene.neil.brown.name> <87v9miydai.fsf@notabene.neil.brown.name> <87ftdgw58w.fsf@notabene.neil.brown.name> Message-ID: <87blo4w57m.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, 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. 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 to ignore the global limits and consider only the limit relevant to the bdi being written to. This approach is already available for BDI_CAP_STRICTLIMIT users (fuse) and should not introduce surprises. This has the desired result of protecting the task from the consequences of large amounts of dirty data queued for other devices. This approach of "only consider the target bdi" 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 - imposes 'strictlimit' handling for any process with PF_LOCAL_THROTTLE set. 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. Note that the worst-case situation with this patch is that the threshold might be calculated as zero. In that case the daemon may block when there are any dirty pages for the final bdi. These will eventually clear and the daemon will be able to proceed. The writing of those dirty pages will increase the apparent throughput of the final bdi and thus increase its threshold for future calculations. Reviewed-by: Jan Kara 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 | 10 ++++++---- mm/vmscan.c | 4 ++-- 6 files changed, 17 insertions(+), 13 deletions(-) diff --git a/drivers/block/loop.c b/drivers/block/loop.c index a42c49e04954..0e13b9fc8dfa 100644 =2D-- a/drivers/block/loop.c +++ b/drivers/block/loop.c @@ -899,7 +899,7 @@ 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..4c9875971de5 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; @@ -1580,6 +1579,9 @@ static void balance_dirty_pages(struct bdi_writeback = *wb, bool strictlimit =3D bdi->capabilities & BDI_CAP_STRICTLIMIT; unsigned long start_time =3D jiffies; =20 + if (current->flags & PF_LOCAL_THROTTLE) + /* This task must only be throttled by its own writeback */ + strictlimit =3D true; for (;;) { unsigned long now =3D jiffies; unsigned long dirty, thresh, bg_thresh; diff --git a/mm/vmscan.c b/mm/vmscan.c index 2e8e690d2813..b776da4bb8c8 100644 =2D-- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -1879,13 +1879,13 @@ 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 2.26.0 --=-=-= Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEEG8Yp69OQ2HB7X0l6Oeye3VZigbkFAl6Lvp0ACgkQOeye3VZi gbljDxAAgPzeTYzedyVP0ZzWworiNpZxQE//mmQdLVH1t7Qv6fxt9RA0xPoSV6yQ ega3Rk8Anir8M5SIvaJPUe1NulnKit4gxWsAgEKn62NOSshq04HQD17EHXWHEcXO t7sfc27Ci7Qm5mHOFFH5hZQQi4cdcRzHqS3vcyS3dW7o5BBwVd0kgXteahONs3iD GLmegXwogtDluXCNm6CK6uVtq1xxzxVfOwiy1/iriA68biDUMXBVB5kY40hFCTJw UcG4bpB1at/dEKOCD7TQVzRYwhk5bsjtEHWbOCMk0NRX/6rxg0USwj/6n3A9cC4F SDgPBVxyFa885uLKQ3x5/hbgdxPZvxBIGboRxgP9A/I2IfEM90rhzTQJW7lV8caZ gS3i/W2UWu/in+VJjY86qvevEL0CXyVXdTxI4Qk761FkWbNPGZr03zoo/1TvCqwt 9LsNkQ2OkUzNk2b+GGtXCtejI8e7tTyxg5y587w/DMzeH//iq2mIKDdAv105Slf1 imdvuE8JnAINltldg6Tlv0+T6xpJXXp88cp8zk6gOZQakSehvjBnFpygaf3XwBiG KiB4nbVmXUTjZvNgv9LFVSSYDOtibeReS0Qpy8H6BLykjak1cGVtNj26tOGKU8iM /rncxk1oYmu2+SRWTS+4rxnOHLlvcIct/1OE1HyMLOyp17YIEWU= =Zlk7 -----END PGP SIGNATURE----- --=-=-=--