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Mon, 04 Dec 2023 01:41:15 +0000 From: NeilBrown To: Al Viro , Christian Brauner , Jens Axboe , Oleg Nesterov , Chuck Lever , Jeff Layton , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-nfs@vger.kernel.org Subject: [PATCH 1/2] Allow a kthread to declare that it calls task_work_run() Date: Mon, 4 Dec 2023 12:36:41 +1100 Message-ID: <20231204014042.6754-2-neilb@suse.de> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20231204014042.6754-1-neilb@suse.de> References: <20231204014042.6754-1-neilb@suse.de> MIME-Version: 1.0 Authentication-Results: smtp-out1.suse.de; none X-Spam-Level: X-Spamd-Result: default: False [0.71 / 50.00]; ARC_NA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; R_MISSING_CHARSET(2.50)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; MIME_GOOD(-0.10)[text/plain]; BROKEN_CONTENT_TYPE(1.50)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; RCVD_COUNT_THREE(0.00)[3]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; 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Kernel-threads generally do not. Because of this some work that is best run in the task_works context (guaranteed that no locks are held) cannot be queued to task_works from kernel threads and so are queued to a (single) work_time to be managed on a work queue. This means that any cost for doing the work is not imposed on the kernel thread, and importantly excessive amounts of work cannot apply back-pressure to reduce the amount of new work queued. I have evidence from a customer site when nfsd (which runs as kernel threads) is being asked to modify many millions of files which causes sufficient memory pressure that some cache (in XFS I think) gets cleaned earlier than would be ideal. When __dput (from the workqueue) calls __dentry_kill, xfs_fs_destroy_inode() needs to synchronously read back previously cached info from storage. This slows down the single thread that is making all the final __dput() calls for all the nfsd threads with the net result that files are added to the delayed_fput_list faster than they are removed, and the system eventually runs out of memory. This happens because there is no back-pressure: the nfsd isn't forced to slow down when __dput() is slow for any reason. To fix this we can change the nfsd threads to call task_work_run() regularly (much like user-space processes do) and allow it to declare this so that work does get queued to task_works rather than to a work queue. This patch adds a new process flag PF_RUNS_TASK_WORK which is now used instead of PF_KTHREAD to determine whether it is sensible to queue something to task_works. This flag is always set for non-kernel threads. task_work_run() is also exported so that it can be called from a module such as nfsd. Signed-off-by: NeilBrown --- fs/file_table.c | 3 ++- fs/namespace.c | 2 +- include/linux/sched.h | 2 +- kernel/fork.c | 2 ++ kernel/task_work.c | 1 + 5 files changed, 7 insertions(+), 3 deletions(-) diff --git a/fs/file_table.c b/fs/file_table.c index ee21b3da9d08..d36cade6e366 100644 --- a/fs/file_table.c +++ b/fs/file_table.c @@ -435,7 +435,8 @@ void fput(struct file *file) if (atomic_long_dec_and_test(&file->f_count)) { struct task_struct *task = current; - if (likely(!in_interrupt() && !(task->flags & PF_KTHREAD))) { + if (likely(!in_interrupt() && + (task->flags & PF_RUNS_TASK_WORK))) { init_task_work(&file->f_rcuhead, ____fput); if (!task_work_add(task, &file->f_rcuhead, TWA_RESUME)) return; diff --git a/fs/namespace.c b/fs/namespace.c index e157efc54023..46d640b70ca9 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -1328,7 +1328,7 @@ static void mntput_no_expire(struct mount *mnt) if (likely(!(mnt->mnt.mnt_flags & MNT_INTERNAL))) { struct task_struct *task = current; - if (likely(!(task->flags & PF_KTHREAD))) { + if (likely((task->flags & PF_RUNS_TASK_WORK))) { init_task_work(&mnt->mnt_rcu, __cleanup_mnt); if (!task_work_add(task, &mnt->mnt_rcu, TWA_RESUME)) return; diff --git a/include/linux/sched.h b/include/linux/sched.h index 77f01ac385f7..e4eebac708e7 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1747,7 +1747,7 @@ extern struct pid *cad_pid; * 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__HOLE__00800000 0x00800000 +#define PF_RUNS_TASK_WORK 0x00800000 /* Will call task_work_run() periodically */ #define PF__HOLE__01000000 0x01000000 #define PF__HOLE__02000000 0x02000000 #define PF_NO_SETAFFINITY 0x04000000 /* Userland is not allowed to meddle with cpus_mask */ diff --git a/kernel/fork.c b/kernel/fork.c index 3b6d20dfb9a8..d612d8f14861 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -2330,6 +2330,8 @@ __latent_entropy struct task_struct *copy_process( p->flags &= ~PF_KTHREAD; if (args->kthread) p->flags |= PF_KTHREAD; + else + p->flags |= PF_RUNS_TASK_WORK; if (args->user_worker) { /* * Mark us a user worker, and block any signal that isn't diff --git a/kernel/task_work.c b/kernel/task_work.c index 95a7e1b7f1da..aec19876e121 100644 --- a/kernel/task_work.c +++ b/kernel/task_work.c @@ -183,3 +183,4 @@ void task_work_run(void) } while (work); } } +EXPORT_SYMBOL(task_work_run); From patchwork Mon Dec 4 01:36:42 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: NeilBrown X-Patchwork-Id: 173035 Return-Path: Delivered-To: ouuuleilei@gmail.com Received: by 2002:a59:bcd1:0:b0:403:3b70:6f57 with SMTP id r17csp2497150vqy; Sun, 3 Dec 2023 17:41:40 -0800 (PST) X-Google-Smtp-Source: AGHT+IGqZFRoCDab0pj020y0zZqUvrQgDjRty5jFu3t067I3F+cTiGYNd31GG47P0UKILyhBbI1t X-Received: by 2002:a05:6a21:6d8b:b0:18f:97c:4f34 with SMTP id wl11-20020a056a216d8b00b0018f097c4f34mr1293097pzb.64.1701654100559; Sun, 03 Dec 2023 17:41:40 -0800 (PST) ARC-Seal: i=1; a=rsa-sha256; t=1701654100; cv=none; d=google.com; s=arc-20160816; b=calLO4FuifmEVWzxmC/AggYCCq1gdBpe96esJlkx6ng/jTXAmeFfa7hobLJrbdZda1 WiTM6Pp7rNnKaBb14J06gqi5h0lDi9CX+ZofD2itaGUva+6vWo/yqtmvN5/aBZmdtL5W +jdbaftIRmDh8AhR2iuDUchsDVXYvc6MZOI1N10A7eSjULRZFjSIyizWc5Stb2Jw7x+I kZycxBy00m4qXr0+W2Ewcxxt4kNtDL+ljav+U60saVIljZXLxutD3jKqWbk8CDHsTSNU S2l0sr35FGR2q3MJ+0ewP6EdBQJmwygAR/YnRqCcwyG8Yxco9fyJWFAR9tL16VVKM/SW e/6w== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:content-transfer-encoding:mime-version :references:in-reply-to:message-id:date:subject:cc:to:from :dkim-signature:dkim-signature; bh=lkymK8+FGpdtWEr2DjC76ilxRN38gXSl47BR9KVwI44=; fh=Ztty36qtkQLs7Q3c1H26mJJAy3kQBJDD0zo+We6C3rQ=; b=IKxiVbxSoBn3PiDn62je7kE3LUMBQirNySvX4uYlxG2DkWTr3+cX9K8JE6z/pCN3xm 0rwsaL6Y4fQpHgeeFcD4bsjq3a+9VmAhikyBY5YVSN/TJWJNxDb1k+OQV/WLL+3a30z8 TV2UQxQkLcjKGZmplfo6fC6JkfVtn7UNowm5VdTkmxMdG1OFjXSvGEC2V27Whl+yUvJm hJcjgENTLghdXNE15PFe6HrKdVYEnpQJqR/fWrptuasS5vW16wjRve1YTfAxNLOPtj9r KC7z9jfn00OEob41k7rDmNEquS0Xgv0BhG1pnuy6LH20/Ozq09lNQszuHg5yXigjE2c/ KtTw== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@suse.de header.s=susede2_rsa header.b=MFcbchrv; dkim=neutral (no key) header.i=@suse.de header.s=susede2_ed25519 header.b=EW5Bh28G; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.37 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=suse.de Received: from snail.vger.email (snail.vger.email. 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Date: Mon, 4 Dec 2023 12:36:42 +1100 Message-ID: <20231204014042.6754-3-neilb@suse.de> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20231204014042.6754-1-neilb@suse.de> References: <20231204014042.6754-1-neilb@suse.de> MIME-Version: 1.0 Authentication-Results: smtp-out2.suse.de; none X-Spam-Level: X-Spamd-Result: default: False [0.71 / 50.00]; RCVD_VIA_SMTP_AUTH(0.00)[]; TO_DN_SOME(0.00)[]; R_MISSING_CHARSET(2.50)[]; BROKEN_CONTENT_TYPE(1.50)[]; RCVD_COUNT_THREE(0.00)[3]; NEURAL_HAM_SHORT(-0.19)[-0.974]; FROM_EQ_ENVFROM(0.00)[]; MIME_TRACE(0.00)[0:+]; BAYES_HAM(-3.00)[100.00%]; ARC_NA(0.00)[]; FROM_HAS_DN(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; MIME_GOOD(-0.10)[text/plain]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; RCPT_COUNT_TWELVE(0.00)[13]; MID_CONTAINS_FROM(1.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[suse.de:email]; FUZZY_BLOCKED(0.00)[rspamd.com]; RCVD_TLS_ALL(0.00)[] X-Spam-Score: 0.71 X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_BLOCKED, SPF_HELO_NONE,SPF_PASS,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-Greylist: Sender passed SPF test, not delayed by milter-greylist-4.6.4 (snail.vger.email [0.0.0.0]); Sun, 03 Dec 2023 17:41:39 -0800 (PST) X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1784313650118344947 X-GMAIL-MSGID: 1784313650118344947 The work of closing a file can have non-trivial cost. Doing it in a separate work queue thread means that cost isn't imposed on the nfsd threads and an imbalance can be created. I have evidence from a customer site when nfsd is being asked to modify many millions of files which causes sufficient memory pressure that some cache (in XFS I think) gets cleaned earlier than would be ideal. When __dput (from the workqueue) calls __dentry_kill, xfs_fs_destroy_inode() needs to synchronously read back previously cached info from storage. This slows down the single thread that is making all the final __dput() calls for all the nfsd threads with the net result that files are added to the delayed_fput_list faster than they are removed, and the system eventually runs out of memory. To avoid this work imbalance that exhausts memory, this patch moves all work for closing files into the nfsd threads. This means that when the work imposes a cost, that cost appears where it would be expected - in the work of the nfsd thread. There are two changes to achieve this. 1/ PF_RUNS_TASK_WORK is set and task_work_run() is called, so that the final __dput() for any file closed by a given nfsd thread is handled by that thread. This ensures that the number of files that are queued for a final close is limited by the number of threads and cannot grow without bound. 2/ Files opened for NFSv3 are never explicitly closed by the client and are kept open by the server in the "filecache", which responds to memory pressure, is garbage collected even when there is no pressure, and sometimes closes files when there is particular need such as for rename. These files currently have filp_close() called in a dedicated work queue, so their __dput() can have no effect on nfsd threads. This patch discards the work queue and instead has each nfsd thread call flip_close() on as many as 8 files from the filecache each time it acts on a client request (or finds there are no pending client requests). If there are more to be closed, more threads are woken. This spreads the work of __dput() over multiple threads and imposes any cost on those threads. The number 8 is somewhat arbitrary. It needs to be greater than 1 to ensure that files are closed more quickly than they can be added to the cache. It needs to be small enough to limit the per-request delays that will be imposed on clients when all threads are busy closing files. Signed-off-by: NeilBrown --- fs/nfsd/filecache.c | 62 ++++++++++++++++++--------------------------- fs/nfsd/filecache.h | 1 + fs/nfsd/nfssvc.c | 6 +++++ 3 files changed, 32 insertions(+), 37 deletions(-) diff --git a/fs/nfsd/filecache.c b/fs/nfsd/filecache.c index ee9c923192e0..55268b7362d4 100644 --- a/fs/nfsd/filecache.c +++ b/fs/nfsd/filecache.c @@ -39,6 +39,7 @@ #include #include #include +#include #include "vfs.h" #include "nfsd.h" @@ -61,13 +62,10 @@ static DEFINE_PER_CPU(unsigned long, nfsd_file_total_age); static DEFINE_PER_CPU(unsigned long, nfsd_file_evictions); struct nfsd_fcache_disposal { - struct work_struct work; spinlock_t lock; struct list_head freeme; }; -static struct workqueue_struct *nfsd_filecache_wq __read_mostly; - static struct kmem_cache *nfsd_file_slab; static struct kmem_cache *nfsd_file_mark_slab; static struct list_lru nfsd_file_lru; @@ -421,10 +419,31 @@ nfsd_file_dispose_list_delayed(struct list_head *dispose) spin_lock(&l->lock); list_move_tail(&nf->nf_lru, &l->freeme); spin_unlock(&l->lock); - queue_work(nfsd_filecache_wq, &l->work); + svc_wake_up(nn->nfsd_serv); } } +/** + * nfsd_file_dispose_some + * + */ +void nfsd_file_dispose_some(struct nfsd_net *nn) +{ + struct nfsd_fcache_disposal *l = nn->fcache_disposal; + LIST_HEAD(dispose); + int i; + + if (list_empty(&l->freeme)) + return; + spin_lock(&l->lock); + for (i = 0; i < 8 && !list_empty(&l->freeme); i++) + list_move(l->freeme.next, &dispose); + spin_unlock(&l->lock); + if (!list_empty(&l->freeme)) + svc_wake_up(nn->nfsd_serv); + nfsd_file_dispose_list(&dispose); +} + /** * nfsd_file_lru_cb - Examine an entry on the LRU list * @item: LRU entry to examine @@ -635,28 +654,8 @@ nfsd_file_close_inode_sync(struct inode *inode) list_del_init(&nf->nf_lru); nfsd_file_free(nf); } - flush_delayed_fput(); -} - -/** - * nfsd_file_delayed_close - close unused nfsd_files - * @work: dummy - * - * Scrape the freeme list for this nfsd_net, and then dispose of them - * all. - */ -static void -nfsd_file_delayed_close(struct work_struct *work) -{ - LIST_HEAD(head); - struct nfsd_fcache_disposal *l = container_of(work, - struct nfsd_fcache_disposal, work); - - spin_lock(&l->lock); - list_splice_init(&l->freeme, &head); - spin_unlock(&l->lock); - - nfsd_file_dispose_list(&head); + /* Flush any delayed fput */ + task_work_run(); } static int @@ -721,10 +720,6 @@ nfsd_file_cache_init(void) return ret; ret = -ENOMEM; - nfsd_filecache_wq = alloc_workqueue("nfsd_filecache", 0, 0); - if (!nfsd_filecache_wq) - goto out; - nfsd_file_slab = kmem_cache_create("nfsd_file", sizeof(struct nfsd_file), 0, 0, NULL); if (!nfsd_file_slab) { @@ -739,7 +734,6 @@ nfsd_file_cache_init(void) goto out_err; } - ret = list_lru_init(&nfsd_file_lru); if (ret) { pr_err("nfsd: failed to init nfsd_file_lru: %d\n", ret); @@ -782,8 +776,6 @@ nfsd_file_cache_init(void) nfsd_file_slab = NULL; kmem_cache_destroy(nfsd_file_mark_slab); nfsd_file_mark_slab = NULL; - destroy_workqueue(nfsd_filecache_wq); - nfsd_filecache_wq = NULL; rhltable_destroy(&nfsd_file_rhltable); goto out; } @@ -829,7 +821,6 @@ nfsd_alloc_fcache_disposal(void) l = kmalloc(sizeof(*l), GFP_KERNEL); if (!l) return NULL; - INIT_WORK(&l->work, nfsd_file_delayed_close); spin_lock_init(&l->lock); INIT_LIST_HEAD(&l->freeme); return l; @@ -838,7 +829,6 @@ nfsd_alloc_fcache_disposal(void) static void nfsd_free_fcache_disposal(struct nfsd_fcache_disposal *l) { - cancel_work_sync(&l->work); nfsd_file_dispose_list(&l->freeme); kfree(l); } @@ -907,8 +897,6 @@ nfsd_file_cache_shutdown(void) fsnotify_wait_marks_destroyed(); kmem_cache_destroy(nfsd_file_mark_slab); nfsd_file_mark_slab = NULL; - destroy_workqueue(nfsd_filecache_wq); - nfsd_filecache_wq = NULL; rhltable_destroy(&nfsd_file_rhltable); for_each_possible_cpu(i) { diff --git a/fs/nfsd/filecache.h b/fs/nfsd/filecache.h index e54165a3224f..bc8c3363bbdf 100644 --- a/fs/nfsd/filecache.h +++ b/fs/nfsd/filecache.h @@ -56,6 +56,7 @@ void nfsd_file_cache_shutdown_net(struct net *net); void nfsd_file_put(struct nfsd_file *nf); struct nfsd_file *nfsd_file_get(struct nfsd_file *nf); void nfsd_file_close_inode_sync(struct inode *inode); +void nfsd_file_dispose_some(struct nfsd_net *nn); bool nfsd_file_is_cached(struct inode *inode); __be32 nfsd_file_acquire_gc(struct svc_rqst *rqstp, struct svc_fh *fhp, unsigned int may_flags, struct nfsd_file **nfp); diff --git a/fs/nfsd/nfssvc.c b/fs/nfsd/nfssvc.c index c7af1095f6b5..02ea16636b54 100644 --- a/fs/nfsd/nfssvc.c +++ b/fs/nfsd/nfssvc.c @@ -13,6 +13,7 @@ #include #include #include +#include #include #include @@ -949,6 +950,7 @@ nfsd(void *vrqstp) } current->fs->umask = 0; + current->flags |= PF_RUNS_TASK_WORK; atomic_inc(&nfsdstats.th_cnt); @@ -963,6 +965,10 @@ nfsd(void *vrqstp) svc_recv(rqstp); validate_process_creds(); + + nfsd_file_dispose_some(nn); + if (task_work_pending(current)) + task_work_run(); } atomic_dec(&nfsdstats.th_cnt);