[v9,8/8] writeback, cgroup: release dying cgwbs by switching attached inodes

Message ID	20210608230225.2078447-9-guro@fb.com (mailing list archive)
State	New, archived
Headers	show Return-Path: <SRS0=dVmx=LC=kvack.org=owner-linux-mm@kernel.org> DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BDF5361178 From: Roman Gushchin <guro@fb.com> To: Andrew Morton <akpm@linux-foundation.org>, Tejun Heo <tj@kernel.org> CC: <linux-fsdevel@vger.kernel.org>, <linux-kernel@vger.kernel.org>, <linux-mm@kvack.org>, Alexander Viro <viro@zeniv.linux.org.uk>, Jan Kara <jack@suse.cz>, Dennis Zhou <dennis@kernel.org>, Dave Chinner <dchinner@redhat.com>, <cgroups@vger.kernel.org>, Roman Gushchin <guro@fb.com> Subject: [PATCH v9 8/8] writeback, cgroup: release dying cgwbs by switching attached inodes Date: Tue, 8 Jun 2021 16:02:25 -0700 Message-ID: <20210608230225.2078447-9-guro@fb.com> In-Reply-To: <20210608230225.2078447-1-guro@fb.com> References: <20210608230225.2078447-1-guro@fb.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain Sender: owner-linux-mm@kvack.org Precedence: bulk
Series	cgroup, blkcg: prevent dirty inodes to pin dying memory cgroups \| expand [v9,0/8] cgroup, blkcg: prevent dirty inodes to pin dying memory cgroups [v9,1/8] writeback, cgroup: do not switch inodes with I_WILL_FREE flag [v9,2/8] writeback, cgroup: add smp_mb() to cgroup_writeback_umount() [v9,3/8] writeback, cgroup: increment isw_nr_in_flight before grabbing an inode [v9,4/8] writeback, cgroup: switch to rcu_work API in inode_switch_wbs() [v9,5/8] writeback, cgroup: keep list of inodes attached to bdi_writeback [v9,6/8] writeback, cgroup: split out the functional part of inode_switch_wbs_work_fn() [v9,7/8] writeback, cgroup: support switching multiple inodes at once [v9,8/8] writeback, cgroup: release dying cgwbs by switching attached inodes

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c index 2d7c5e1e32e7..49b33300b1b8 100644 --- a/fs/fs-writeback.c +++ b/fs/fs-writeback.c @@ -225,6 +225,12 @@ void wb_wait_for_completion(struct wb_completion *done) /* one round can affect upto 5 slots */ #define WB_FRN_MAX_IN_FLIGHT 1024 /* don't queue too many concurrently */ +/* + * Maximum inodes per isw. A specific value has been chosen to make + * struct inode_switch_wbs_context fit into 1024 bytes kmalloc. + */ +#define WB_MAX_INODES_PER_ISW 115 + static atomic_t isw_nr_in_flight = ATOMIC_INIT(0); static struct workqueue_struct *isw_wq; @@ -503,6 +509,24 @@ static void inode_switch_wbs_work_fn(struct work_struct *work) atomic_dec(&isw_nr_in_flight); } +static bool inode_prepare_wbs_switch(struct inode *inode, + struct bdi_writeback *new_wb) +{ + /* while holding I_WB_SWITCH, no one else can update the association */ + spin_lock(&inode->i_lock); + if (!(inode->i_sb->s_flags & SB_ACTIVE) || + inode->i_state & (I_WB_SWITCH | I_FREEING | I_WILL_FREE) || + inode_to_wb(inode) == new_wb) { + spin_unlock(&inode->i_lock); + return false; + } + inode->i_state |= I_WB_SWITCH; + __iget(inode); + spin_unlock(&inode->i_lock); + + return true; +} + /** * inode_switch_wbs - change the wb association of an inode * @inode: target inode @@ -540,17 +564,8 @@ static void inode_switch_wbs(struct inode *inode, int new_wb_id) if (!isw->new_wb) goto out_free; - /* while holding I_WB_SWITCH, no one else can update the association */ - spin_lock(&inode->i_lock); - if (!(inode->i_sb->s_flags & SB_ACTIVE) || - inode->i_state & (I_WB_SWITCH | I_FREEING | I_WILL_FREE) || - inode_to_wb(inode) == isw->new_wb) { - spin_unlock(&inode->i_lock); + if (!inode_prepare_wbs_switch(inode, isw->new_wb)) goto out_free; - } - inode->i_state |= I_WB_SWITCH; - __iget(inode); - spin_unlock(&inode->i_lock); isw->inodes[0] = inode; @@ -571,6 +586,73 @@ static void inode_switch_wbs(struct inode *inode, int new_wb_id) kfree(isw); } +/** + * cleanup_offline_cgwb - detach associated inodes + * @wb: target wb + * + * Switch all inodes attached to @wb to a nearest living ancestor's wb in order + * to eventually release the dying @wb. Returns %true if not all inodes were + * switched and the function has to be restarted. + */ +bool cleanup_offline_cgwb(struct bdi_writeback *wb) +{ + struct cgroup_subsys_state *memcg_css; + struct inode_switch_wbs_context *isw; + struct inode *inode; + int nr; + bool restart = false; + + isw = kzalloc(sizeof(*isw) + WB_MAX_INODES_PER_ISW * + sizeof(struct inode *), GFP_KERNEL); + if (!isw) + return restart; + + atomic_inc(&isw_nr_in_flight); + + for (memcg_css = wb->memcg_css->parent; memcg_css; + memcg_css = memcg_css->parent) { + isw->new_wb = wb_get_create(wb->bdi, memcg_css, GFP_KERNEL); + if (isw->new_wb) + break; + } + if (unlikely(!isw->new_wb)) + isw->new_wb = &wb->bdi->wb; /* wb_get() is noop for bdi's wb */ + + nr = 0; + spin_lock(&wb->list_lock); + list_for_each_entry(inode, &wb->b_attached, i_io_list) { + if (!inode_prepare_wbs_switch(inode, isw->new_wb)) + continue; + + isw->inodes[nr++] = inode; + + if (nr >= WB_MAX_INODES_PER_ISW - 1) { + restart = true; + break; + } + } + spin_unlock(&wb->list_lock); + + /* no attached inodes? bail out */ + if (nr == 0) { + atomic_dec(&isw_nr_in_flight); + wb_put(isw->new_wb); + kfree(isw); + return restart; + } + + /* + * In addition to synchronizing among switchers, I_WB_SWITCH tells + * the RCU protected stat update paths to grab the i_page + * lock so that stat transfer can synchronize against them. + * Let's continue after I_WB_SWITCH is guaranteed to be visible. + */ + INIT_RCU_WORK(&isw->work, inode_switch_wbs_work_fn); + queue_rcu_work(isw_wq, &isw->work); + + return restart; +} + /** * wbc_attach_and_unlock_inode - associate wbc with target inode and unlock it * @wbc: writeback_control of interest diff --git a/include/linux/backing-dev-defs.h b/include/linux/backing-dev-defs.h index 63f52ad2ce7a..1d7edad9914f 100644 --- a/include/linux/backing-dev-defs.h +++ b/include/linux/backing-dev-defs.h @@ -155,6 +155,7 @@ struct bdi_writeback { struct list_head memcg_node; /* anchored at memcg->cgwb_list */ struct list_head blkcg_node; /* anchored at blkcg->cgwb_list */ struct list_head b_attached; /* attached inodes, protected by list_lock */ + struct list_head offline_node; /* anchored at offline_cgwbs */ union { struct work_struct release_work; diff --git a/include/linux/writeback.h b/include/linux/writeback.h index 9ef50176f3a1..667e86cfbdcf 100644 --- a/include/linux/writeback.h +++ b/include/linux/writeback.h @@ -221,6 +221,7 @@ void wbc_account_cgroup_owner(struct writeback_control *wbc, struct page *page, int cgroup_writeback_by_id(u64 bdi_id, int memcg_id, unsigned long nr_pages, enum wb_reason reason, struct wb_completion *done); void cgroup_writeback_umount(void); +bool cleanup_offline_cgwb(struct bdi_writeback *wb); /** * inode_attach_wb - associate an inode with its wb diff --git a/mm/backing-dev.c b/mm/backing-dev.c index 54c5dc4b8c24..52eaeee40da3 100644 --- a/mm/backing-dev.c +++ b/mm/backing-dev.c @@ -371,12 +371,16 @@ static void wb_exit(struct bdi_writeback *wb) #include <linux/memcontrol.h> /* - * cgwb_lock protects bdi->cgwb_tree, blkcg->cgwb_list, and memcg->cgwb_list. - * bdi->cgwb_tree is also RCU protected. + * cgwb_lock protects bdi->cgwb_tree, blkcg->cgwb_list, offline_cgwbs and + * memcg->cgwb_list. bdi->cgwb_tree is also RCU protected. */ static DEFINE_SPINLOCK(cgwb_lock); static struct workqueue_struct *cgwb_release_wq; +static LIST_HEAD(offline_cgwbs); +static void cleanup_offline_cgwbs_workfn(struct work_struct *work); +static DECLARE_WORK(cleanup_offline_cgwbs_work, cleanup_offline_cgwbs_workfn); + static void cgwb_release_workfn(struct work_struct *work) { struct bdi_writeback *wb = container_of(work, struct bdi_writeback, @@ -395,6 +399,11 @@ static void cgwb_release_workfn(struct work_struct *work) fprop_local_destroy_percpu(&wb->memcg_completions); percpu_ref_exit(&wb->refcnt); + + spin_lock_irq(&cgwb_lock); + list_del(&wb->offline_node); + spin_unlock_irq(&cgwb_lock); + wb_exit(wb); WARN_ON_ONCE(!list_empty(&wb->b_attached)); kfree_rcu(wb, rcu); @@ -414,6 +423,7 @@ static void cgwb_kill(struct bdi_writeback *wb) WARN_ON(!radix_tree_delete(&wb->bdi->cgwb_tree, wb->memcg_css->id)); list_del(&wb->memcg_node); list_del(&wb->blkcg_node); + list_add(&wb->offline_node, &offline_cgwbs); percpu_ref_kill(&wb->refcnt); } @@ -635,6 +645,57 @@ static void cgwb_bdi_unregister(struct backing_dev_info *bdi) mutex_unlock(&bdi->cgwb_release_mutex); } +/** + * cleanup_offline_cgwbs - try to release dying cgwbs + * + * Try to release dying cgwbs by switching attached inodes to the nearest + * living ancestor's writeback. Processed wbs are placed at the end + * of the list to guarantee the forward progress. + * + * Should be called with the acquired cgwb_lock lock, which might + * be released and re-acquired in the process. + */ +static void cleanup_offline_cgwbs_workfn(struct work_struct *work) +{ + struct bdi_writeback *wb; + LIST_HEAD(processed); + + spin_lock_irq(&cgwb_lock); + + while (!list_empty(&offline_cgwbs)) { + wb = list_first_entry(&offline_cgwbs, struct bdi_writeback, + offline_node); + list_move(&wb->offline_node, &processed); + + /* + * If wb is dirty, cleaning up the writeback by switching + * attached inodes will result in an effective removal of any + * bandwidth restrictions, which isn't the goal. Instead, + * it can be postponed until the next time, when all io + * will be likely completed. If in the meantime some inodes + * will get re-dirtied, they should be eventually switched to + * a new cgwb. + */ + if (wb_has_dirty_io(wb)) + continue; + + if (!wb_tryget(wb)) + continue; + + spin_unlock_irq(&cgwb_lock); + while (cleanup_offline_cgwb(wb)) + cond_resched(); + spin_lock_irq(&cgwb_lock); + + wb_put(wb); + } + + if (!list_empty(&processed)) + list_splice_tail(&processed, &offline_cgwbs); + + spin_unlock_irq(&cgwb_lock); +} + /** * wb_memcg_offline - kill all wb's associated with a memcg being offlined * @memcg: memcg being offlined @@ -651,6 +712,8 @@ void wb_memcg_offline(struct mem_cgroup *memcg) cgwb_kill(wb); memcg_cgwb_list->next = NULL; /* prevent new wb's */ spin_unlock_irq(&cgwb_lock); + + queue_work(system_unbound_wq, &cleanup_offline_cgwbs_work); } /**

[v9,8/8] writeback, cgroup: release dying cgwbs by switching attached inodes

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