xfs: multithreaded iwalk implementation

Create a parallel iwalk implementation and switch quotacheck to use it.

Signed-off-by: Darrick J. Wong <[e-mail]>
Reviewed-by: Brian Foster <[e-mail]>

fs/xfs/Makefile

···
 				   xfs_message.o \
 				   xfs_mount.o \
 				   xfs_mru_cache.o \
+				   xfs_pwork.o \
 				   xfs_reflink.o \
 				   xfs_stats.o \
 				   xfs_super.o \

fs/xfs/xfs_globals.c

···
 #else
 	.bug_on_assert		=	false,	/* assert failures WARN() */
 #endif
+#ifdef DEBUG
+	.pwork_threads		=	-1,	/* automatic thread detection */
+#endif
 };

fs/xfs/xfs_iwalk.c

···
 #include "xfs_icache.h"
 #include "xfs_health.h"
 #include "xfs_trans.h"
+#include "xfs_pwork.h"
 
 /*
  * Walking Inodes in the Filesystem
···
  */
 
 struct xfs_iwalk_ag {
+	/* parallel work control data; will be null if single threaded */
+	struct xfs_pwork		pwork;
+
 	struct xfs_mount		*mp;
 	struct xfs_trans		*tp;
 
···
 
 		trace_xfs_iwalk_ag_rec(mp, agno, irec);
 
+		if (xfs_pwork_want_abort(&iwag->pwork))
+			return 0;
+
 		if (iwag->inobt_walk_fn) {
 			error = iwag->inobt_walk_fn(mp, tp, agno, irec,
 					iwag->data);
···
 			continue;
 
 		for (j = 0; j < XFS_INODES_PER_CHUNK; j++) {
+			if (xfs_pwork_want_abort(&iwag->pwork))
+				return 0;
+
 			/* Skip if this inode is free */
 			if (XFS_INOBT_MASK(j) & irec->ir_free)
 				continue;
···
 		struct xfs_inobt_rec_incore	*irec;
 
 		cond_resched();
+		if (xfs_pwork_want_abort(&iwag->pwork))
+			goto out;
 
 		/* Fetch the inobt record. */
 		irec = &iwag->recs[iwag->nr_recs];
···
 		.sz_recs	= xfs_iwalk_prefetch(inode_records),
 		.trim_start	= 1,
 		.skip_empty	= 1,
+		.pwork		= XFS_PWORK_SINGLE_THREADED,
 	};
 	xfs_agnumber_t		agno = XFS_INO_TO_AGNO(mp, startino);
 	int			error;
···
 
 	xfs_iwalk_free(&iwag);
 	return error;
+}
+
+/* Run per-thread iwalk work. */
+static int
+xfs_iwalk_ag_work(
+	struct xfs_mount	*mp,
+	struct xfs_pwork	*pwork)
+{
+	struct xfs_iwalk_ag	*iwag;
+	int			error = 0;
+
+	iwag = container_of(pwork, struct xfs_iwalk_ag, pwork);
+	if (xfs_pwork_want_abort(pwork))
+		goto out;
+
+	error = xfs_iwalk_alloc(iwag);
+	if (error)
+		goto out;
+
+	error = xfs_iwalk_ag(iwag);
+	xfs_iwalk_free(iwag);
+out:
+	kmem_free(iwag);
+	return error;
+}
+
+/*
+ * Walk all the inodes in the filesystem using multiple threads to process each
+ * AG.
+ */
+int
+xfs_iwalk_threaded(
+	struct xfs_mount	*mp,
+	xfs_ino_t		startino,
+	xfs_iwalk_fn		iwalk_fn,
+	unsigned int		inode_records,
+	void			*data)
+{
+	struct xfs_pwork_ctl	pctl;
+	xfs_agnumber_t		agno = XFS_INO_TO_AGNO(mp, startino);
+	unsigned int		nr_threads;
+	int			error;
+
+	ASSERT(agno < mp->m_sb.sb_agcount);
+
+	nr_threads = xfs_pwork_guess_datadev_parallelism(mp);
+	error = xfs_pwork_init(mp, &pctl, xfs_iwalk_ag_work, "xfs_iwalk",
+			nr_threads);
+	if (error)
+		return error;
+
+	for (; agno < mp->m_sb.sb_agcount; agno++) {
+		struct xfs_iwalk_ag	*iwag;
+
+		if (xfs_pwork_ctl_want_abort(&pctl))
+			break;
+
+		iwag = kmem_zalloc(sizeof(struct xfs_iwalk_ag), KM_SLEEP);
+		iwag->mp = mp;
+		iwag->iwalk_fn = iwalk_fn;
+		iwag->data = data;
+		iwag->startino = startino;
+		iwag->sz_recs = xfs_iwalk_prefetch(inode_records);
+		xfs_pwork_queue(&pctl, &iwag->pwork);
+		startino = XFS_AGINO_TO_INO(mp, agno + 1, 0);
+	}
+
+	return xfs_pwork_destroy(&pctl);
 }
 
 /*
···
 		.data		= data,
 		.startino	= startino,
 		.sz_recs	= xfs_inobt_walk_prefetch(inobt_records),
+		.pwork		= XFS_PWORK_SINGLE_THREADED,
 	};
 	xfs_agnumber_t		agno = XFS_INO_TO_AGNO(mp, startino);
 	int			error;

fs/xfs/xfs_iwalk.h

···
 
 int xfs_iwalk(struct xfs_mount *mp, struct xfs_trans *tp, xfs_ino_t startino,
 		xfs_iwalk_fn iwalk_fn, unsigned int inode_records, void *data);
+int xfs_iwalk_threaded(struct xfs_mount *mp, xfs_ino_t startino,
+		xfs_iwalk_fn iwalk_fn, unsigned int inode_records, void *data);
 
 /* Walk all inode btree records in the filesystem starting from @startino. */
 typedef int (*xfs_inobt_walk_fn)(struct xfs_mount *mp, struct xfs_trans *tp,

fs/xfs/xfs_pwork.c

···
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2019 Oracle.  All Rights Reserved.
+ * Author: Darrick J. Wong <[e-mail]>
+ */
+#include "xfs.h"
+#include "xfs_fs.h"
+#include "xfs_shared.h"
+#include "xfs_format.h"
+#include "xfs_log_format.h"
+#include "xfs_trans_resv.h"
+#include "xfs_mount.h"
+#include "xfs_trace.h"
+#include "xfs_sysctl.h"
+#include "xfs_pwork.h"
+
+/*
+ * Parallel Work Queue
+ * ===================
+ *
+ * Abstract away the details of running a large and "obviously" parallelizable
+ * task across multiple CPUs.  Callers initialize the pwork control object with
+ * a desired level of parallelization and a work function.  Next, they embed
+ * struct xfs_pwork in whatever structure they use to pass work context to a
+ * worker thread and queue that pwork.  The work function will be passed the
+ * pwork item when it is run (from process context) and any returned error will
+ * be recorded in xfs_pwork_ctl.error.  Work functions should check for errors
+ * and abort if necessary; the non-zeroness of xfs_pwork_ctl.error does not
+ * stop workqueue item processing.
+ *
+ * This is the rough equivalent of the xfsprogs workqueue code, though we can't
+ * reuse that name here.
+ */
+
+/* Invoke our caller's function. */
+static void
+xfs_pwork_work(
+	struct work_struct	*work)
+{
+	struct xfs_pwork	*pwork;
+	struct xfs_pwork_ctl	*pctl;
+	int			error;
+
+	pwork = container_of(work, struct xfs_pwork, work);
+	pctl = pwork->pctl;
+	error = pctl->work_fn(pctl->mp, pwork);
+	if (error && !pctl->error)
+		pctl->error = error;
+}
+
+/*
+ * Set up control data for parallel work.  @work_fn is the function that will
+ * be called.  @tag will be written into the kernel threads.  @nr_threads is
+ * the level of parallelism desired, or 0 for no limit.
+ */
+int
+xfs_pwork_init(
+	struct xfs_mount	*mp,
+	struct xfs_pwork_ctl	*pctl,
+	xfs_pwork_work_fn	work_fn,
+	const char		*tag,
+	unsigned int		nr_threads)
+{
+#ifdef DEBUG
+	if (xfs_globals.pwork_threads >= 0)
+		nr_threads = xfs_globals.pwork_threads;
+#endif
+	trace_xfs_pwork_init(mp, nr_threads, current->pid);
+
+	pctl->wq = alloc_workqueue("%s-%d", WQ_FREEZABLE, nr_threads, tag,
+			current->pid);
+	if (!pctl->wq)
+		return -ENOMEM;
+	pctl->work_fn = work_fn;
+	pctl->error = 0;
+	pctl->mp = mp;
+
+	return 0;
+}
+
+/* Queue some parallel work. */
+void
+xfs_pwork_queue(
+	struct xfs_pwork_ctl	*pctl,
+	struct xfs_pwork	*pwork)
+{
+	INIT_WORK(&pwork->work, xfs_pwork_work);
+	pwork->pctl = pctl;
+	queue_work(pctl->wq, &pwork->work);
+}
+
+/* Wait for the work to finish and tear down the control structure. */
+int
+xfs_pwork_destroy(
+	struct xfs_pwork_ctl	*pctl)
+{
+	destroy_workqueue(pctl->wq);
+	pctl->wq = NULL;
+	return pctl->error;
+}
+
+/*
+ * Return the amount of parallelism that the data device can handle, or 0 for
+ * no limit.
+ */
+unsigned int
+xfs_pwork_guess_datadev_parallelism(
+	struct xfs_mount	*mp)
+{
+	struct xfs_buftarg	*btp = mp->m_ddev_targp;
+
+	/*
+	 * For now we'll go with the most conservative setting possible,
+	 * which is two threads for an SSD and 1 thread everywhere else.
+	 */
+	return blk_queue_nonrot(btp->bt_bdev->bd_queue) ? 2 : 1;
+}

fs/xfs/xfs_pwork.h

···
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Copyright (C) 2019 Oracle.  All Rights Reserved.
+ * Author: Darrick J. Wong <[e-mail]>
+ */
+#ifndef __XFS_PWORK_H__
+#define __XFS_PWORK_H__
+
+struct xfs_pwork;
+struct xfs_mount;
+
+typedef int (*xfs_pwork_work_fn)(struct xfs_mount *mp, struct xfs_pwork *pwork);
+
+/*
+ * Parallel work coordination structure.
+ */
+struct xfs_pwork_ctl {
+	struct workqueue_struct	*wq;
+	struct xfs_mount	*mp;
+	xfs_pwork_work_fn	work_fn;
+	int			error;
+};
+
+/*
+ * Embed this parallel work control item inside your own work structure,
+ * then queue work with it.
+ */
+struct xfs_pwork {
+	struct work_struct	work;
+	struct xfs_pwork_ctl	*pctl;
+};
+
+#define XFS_PWORK_SINGLE_THREADED	{ .pctl = NULL }
+
+/* Have we been told to abort? */
+static inline bool
+xfs_pwork_ctl_want_abort(
+	struct xfs_pwork_ctl	*pctl)
+{
+	return pctl && pctl->error;
+}
+
+/* Have we been told to abort? */
+static inline bool
+xfs_pwork_want_abort(
+	struct xfs_pwork	*pwork)
+{
+	return xfs_pwork_ctl_want_abort(pwork->pctl);
+}
+
+int xfs_pwork_init(struct xfs_mount *mp, struct xfs_pwork_ctl *pctl,
+		xfs_pwork_work_fn work_fn, const char *tag,
+		unsigned int nr_threads);
+void xfs_pwork_queue(struct xfs_pwork_ctl *pctl, struct xfs_pwork *pwork);
+int xfs_pwork_destroy(struct xfs_pwork_ctl *pctl);
+unsigned int xfs_pwork_guess_datadev_parallelism(struct xfs_mount *mp);
+
+#endif /* __XFS_PWORK_H__ */

fs/xfs/xfs_qm.c

···
 		flags |= XFS_PQUOTA_CHKD;
 	}
 
-	error = xfs_iwalk(mp, NULL, 0, xfs_qm_dqusage_adjust, 0, NULL);
+	error = xfs_iwalk_threaded(mp, 0, xfs_qm_dqusage_adjust, 0, NULL);
 	if (error)
 		goto error_return;
 

fs/xfs/xfs_sysctl.h

···
 extern xfs_param_t	xfs_params;
 
 struct xfs_globals {
+#ifdef DEBUG
+	int	pwork_threads;		/* parallel workqueue threads */
+#endif
 	int	log_recovery_delay;	/* log recovery delay (secs) */
 	int	mount_delay;		/* mount setup delay (secs) */
 	bool	bug_on_assert;		/* BUG() the kernel on assert failure */

fs/xfs/xfs_sysfs.c

···
 }
 XFS_SYSFS_ATTR_RW(always_cow);
 
+#ifdef DEBUG
+/*
+ * Override how many threads the parallel work queue is allowed to create.
+ * This has to be a debug-only global (instead of an errortag) because one of
+ * the main users of parallel workqueues is mount time quotacheck.
+ */
+STATIC ssize_t
+pwork_threads_store(
+	struct kobject	*kobject,
+	const char	*buf,
+	size_t		count)
+{
+	int		ret;
+	int		val;
+
+	ret = kstrtoint(buf, 0, &val);
+	if (ret)
+		return ret;
+
+	if (val < -1 || val > num_possible_cpus())
+		return -EINVAL;
+
+	xfs_globals.pwork_threads = val;
+
+	return count;
+}
+
+STATIC ssize_t
+pwork_threads_show(
+	struct kobject	*kobject,
+	char		*buf)
+{
+	return snprintf(buf, PAGE_SIZE, "%d\n", xfs_globals.pwork_threads);
+}
+XFS_SYSFS_ATTR_RW(pwork_threads);
+#endif /* DEBUG */
+
 static struct attribute *xfs_dbg_attrs[] = {
 	ATTR_LIST(bug_on_assert),
 	ATTR_LIST(log_recovery_delay),
 	ATTR_LIST(mount_delay),
 	ATTR_LIST(always_cow),
+#ifdef DEBUG
+	ATTR_LIST(pwork_threads),
+#endif
 	NULL,
 };
 

fs/xfs/xfs_trace.h

···
 		  __entry->startino, __entry->freemask)
 )
 
+TRACE_EVENT(xfs_pwork_init,
+	TP_PROTO(struct xfs_mount *mp, unsigned int nr_threads, pid_t pid),
+	TP_ARGS(mp, nr_threads, pid),
+	TP_STRUCT__entry(
+		__field(dev_t, dev)
+		__field(unsigned int, nr_threads)
+		__field(pid_t, pid)
+	),
+	TP_fast_assign(
+		__entry->dev = mp->m_super->s_dev;
+		__entry->nr_threads = nr_threads;
+		__entry->pid = pid;
+	),
+	TP_printk("dev %d:%d nr_threads %u pid %u",
+		  MAJOR(__entry->dev), MINOR(__entry->dev),
+		  __entry->nr_threads, __entry->pid)
+)
+
 #endif /* _TRACE_XFS_H */
 
 #undef TRACE_INCLUDE_PATH