1 files changed, 432 insertions, 0 deletions

diff --git a/fs/xfs/xfs_discard.c b/fs/xfs/xfs_discard.c
new file mode 100644
index 000000000..d5787991b
--- /dev/null
+++ b/fs/xfs/xfs_discard.c
@@ -0,0 +1,432 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2010, 2023 Red Hat, Inc.
+ * All Rights Reserved.
+ */
+#include "xfs.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_btree.h"
+#include "xfs_alloc_btree.h"
+#include "xfs_alloc.h"
+#include "xfs_discard.h"
+#include "xfs_error.h"
+#include "xfs_extent_busy.h"
+#include "xfs_trace.h"
+#include "xfs_log.h"
+#include "xfs_ag.h"
+
+/*
+ * Notes on an efficient, low latency fstrim algorithm
+ *
+ * We need to walk the filesystem free space and issue discards on the free
+ * space that meet the search criteria (size and location). We cannot issue
+ * discards on extents that might be in use, or are so recently in use they are
+ * still marked as busy. To serialise against extent state changes whilst we are
+ * gathering extents to trim, we must hold the AGF lock to lock out other
+ * allocations and extent free operations that might change extent state.
+ *
+ * However, we cannot just hold the AGF for the entire AG free space walk whilst
+ * we issue discards on each free space that is found. Storage devices can have
+ * extremely slow discard implementations (e.g. ceph RBD) and so walking a
+ * couple of million free extents and issuing synchronous discards on each
+ * extent can take a *long* time. Whilst we are doing this walk, nothing else
+ * can access the AGF, and we can stall transactions and hence the log whilst
+ * modifications wait for the AGF lock to be released. This can lead hung tasks
+ * kicking the hung task timer and rebooting the system. This is bad.
+ *
+ * Hence we need to take a leaf from the bulkstat playbook. It takes the AGI
+ * lock, gathers a range of inode cluster buffers that are allocated, drops the
+ * AGI lock and then reads all the inode cluster buffers and processes them. It
+ * loops doing this, using a cursor to keep track of where it is up to in the AG
+ * for each iteration to restart the INOBT lookup from.
+ *
+ * We can't do this exactly with free space - once we drop the AGF lock, the
+ * state of the free extent is out of our control and we cannot run a discard
+ * safely on it in this situation. Unless, of course, we've marked the free
+ * extent as busy and undergoing a discard operation whilst we held the AGF
+ * locked.
+ *
+ * This is exactly how online discard works - free extents are marked busy when
+ * they are freed, and once the extent free has been committed to the journal,
+ * the busy extent record is marked as "undergoing discard" and the discard is
+ * then issued on the free extent. Once the discard completes, the busy extent
+ * record is removed and the extent is able to be allocated again.
+ *
+ * In the context of fstrim, if we find a free extent we need to discard, we
+ * don't have to discard it immediately. All we need to do it record that free
+ * extent as being busy and under discard, and all the allocation routines will
+ * now avoid trying to allocate it. Hence if we mark the extent as busy under
+ * the AGF lock, we can safely discard it without holding the AGF lock because
+ * nothing will attempt to allocate that free space until the discard completes.
+ *
+ * This also allows us to issue discards asynchronously like we do with online
+ * discard, and so for fast devices fstrim will run much faster as we can have
+ * multiple discard operations in flight at once, as well as pipeline the free
+ * extent search so that it overlaps in flight discard IO.
+ */
+
+struct workqueue_struct *xfs_discard_wq;
+
+static void
+xfs_discard_endio_work(
+	struct work_struct	*work)
+{
+	struct xfs_busy_extents	*extents =
+		container_of(work, struct xfs_busy_extents, endio_work);
+
+	xfs_extent_busy_clear(extents->mount, &extents->extent_list, false);
+	kmem_free(extents->owner);
+}
+
+/*
+ * Queue up the actual completion to a thread to avoid IRQ-safe locking for
+ * pagb_lock.
+ */
+static void
+xfs_discard_endio(
+	struct bio		*bio)
+{
+	struct xfs_busy_extents	*extents = bio->bi_private;
+
+	INIT_WORK(&extents->endio_work, xfs_discard_endio_work);
+	queue_work(xfs_discard_wq, &extents->endio_work);
+	bio_put(bio);
+}
+
+/*
+ * Walk the discard list and issue discards on all the busy extents in the
+ * list. We plug and chain the bios so that we only need a single completion
+ * call to clear all the busy extents once the discards are complete.
+ */
+int
+xfs_discard_extents(
+	struct xfs_mount	*mp,
+	struct xfs_busy_extents	*extents)
+{
+	struct xfs_extent_busy	*busyp;
+	struct bio		*bio = NULL;
+	struct blk_plug		plug;
+	int			error = 0;
+
+	blk_start_plug(&plug);
+	list_for_each_entry(busyp, &extents->extent_list, list) {
+		trace_xfs_discard_extent(mp, busyp->agno, busyp->bno,
+					 busyp->length);
+
+		error = __blkdev_issue_discard(mp->m_ddev_targp->bt_bdev,
+				XFS_AGB_TO_DADDR(mp, busyp->agno, busyp->bno),
+				XFS_FSB_TO_BB(mp, busyp->length),
+				GFP_NOFS, &bio);
+		if (error && error != -EOPNOTSUPP) {
+			xfs_info(mp,
+	 "discard failed for extent [0x%llx,%u], error %d",
+				 (unsigned long long)busyp->bno,
+				 busyp->length,
+				 error);
+			break;
+		}
+	}
+
+	if (bio) {
+		bio->bi_private = extents;
+		bio->bi_end_io = xfs_discard_endio;
+		submit_bio(bio);
+	} else {
+		xfs_discard_endio_work(&extents->endio_work);
+	}
+	blk_finish_plug(&plug);
+
+	return error;
+}
+
+
+static int
+xfs_trim_gather_extents(
+	struct xfs_perag	*pag,
+	xfs_daddr_t		start,
+	xfs_daddr_t		end,
+	xfs_daddr_t		minlen,
+	struct xfs_alloc_rec_incore *tcur,
+	struct xfs_busy_extents	*extents,
+	uint64_t		*blocks_trimmed)
+{
+	struct xfs_mount	*mp = pag->pag_mount;
+	struct xfs_btree_cur	*cur;
+	struct xfs_buf		*agbp;
+	int			error;
+	int			i;
+	int			batch = 100;
+
+	/*
+	 * Force out the log.  This means any transactions that might have freed
+	 * space before we take the AGF buffer lock are now on disk, and the
+	 * volatile disk cache is flushed.
+	 */
+	xfs_log_force(mp, XFS_LOG_SYNC);
+
+	error = xfs_alloc_read_agf(pag, NULL, 0, &agbp);
+	if (error)
+		return error;
+
+	cur = xfs_allocbt_init_cursor(mp, NULL, agbp, pag, XFS_BTNUM_CNT);
+
+	/*
+	 * Look up the extent length requested in the AGF and start with it.
+	 */
+	if (tcur->ar_startblock == NULLAGBLOCK)
+		error = xfs_alloc_lookup_ge(cur, 0, tcur->ar_blockcount, &i);
+	else
+		error = xfs_alloc_lookup_le(cur, tcur->ar_startblock,
+				tcur->ar_blockcount, &i);
+	if (error)
+		goto out_del_cursor;
+	if (i == 0) {
+		/* nothing of that length left in the AG, we are done */
+		tcur->ar_blockcount = 0;
+		goto out_del_cursor;
+	}
+
+	/*
+	 * Loop until we are done with all extents that are large
+	 * enough to be worth discarding or we hit batch limits.
+	 */
+	while (i) {
+		xfs_agblock_t	fbno;
+		xfs_extlen_t	flen;
+		xfs_daddr_t	dbno;
+		xfs_extlen_t	dlen;
+
+		error = xfs_alloc_get_rec(cur, &fbno, &flen, &i);
+		if (error)
+			break;
+		if (XFS_IS_CORRUPT(mp, i != 1)) {
+			error = -EFSCORRUPTED;
+			break;
+		}
+
+		if (--batch <= 0) {
+			/*
+			 * Update the cursor to point at this extent so we
+			 * restart the next batch from this extent.
+			 */
+			tcur->ar_startblock = fbno;
+			tcur->ar_blockcount = flen;
+			break;
+		}
+
+		/*
+		 * use daddr format for all range/len calculations as that is
+		 * the format the range/len variables are supplied in by
+		 * userspace.
+		 */
+		dbno = XFS_AGB_TO_DADDR(mp, pag->pag_agno, fbno);
+		dlen = XFS_FSB_TO_BB(mp, flen);
+
+		/*
+		 * Too small?  Give up.
+		 */
+		if (dlen < minlen) {
+			trace_xfs_discard_toosmall(mp, pag->pag_agno, fbno, flen);
+			tcur->ar_blockcount = 0;
+			break;
+		}
+
+		/*
+		 * If the extent is entirely outside of the range we are
+		 * supposed to discard skip it.  Do not bother to trim
+		 * down partially overlapping ranges for now.
+		 */
+		if (dbno + dlen < start || dbno > end) {
+			trace_xfs_discard_exclude(mp, pag->pag_agno, fbno, flen);
+			goto next_extent;
+		}
+
+		/*
+		 * If any blocks in the range are still busy, skip the
+		 * discard and try again the next time.
+		 */
+		if (xfs_extent_busy_search(mp, pag, fbno, flen)) {
+			trace_xfs_discard_busy(mp, pag->pag_agno, fbno, flen);
+			goto next_extent;
+		}
+
+		xfs_extent_busy_insert_discard(pag, fbno, flen,
+				&extents->extent_list);
+		*blocks_trimmed += flen;
+next_extent:
+		error = xfs_btree_decrement(cur, 0, &i);
+		if (error)
+			break;
+
+		/*
+		 * If there's no more records in the tree, we are done. Set the
+		 * cursor block count to 0 to indicate to the caller that there
+		 * is no more extents to search.
+		 */
+		if (i == 0)
+			tcur->ar_blockcount = 0;
+	}
+
+	/*
+	 * If there was an error, release all the gathered busy extents because
+	 * we aren't going to issue a discard on them any more.
+	 */
+	if (error)
+		xfs_extent_busy_clear(mp, &extents->extent_list, false);
+out_del_cursor:
+	xfs_btree_del_cursor(cur, error);
+	xfs_buf_relse(agbp);
+	return error;
+}
+
+static bool
+xfs_trim_should_stop(void)
+{
+	return fatal_signal_pending(current) || freezing(current);
+}
+
+/*
+ * Iterate the free list gathering extents and discarding them. We need a cursor
+ * for the repeated iteration of gather/discard loop, so use the longest extent
+ * we found in the last batch as the key to start the next.
+ */
+static int
+xfs_trim_extents(
+	struct xfs_perag	*pag,
+	xfs_daddr_t		start,
+	xfs_daddr_t		end,
+	xfs_daddr_t		minlen,
+	uint64_t		*blocks_trimmed)
+{
+	struct xfs_alloc_rec_incore tcur = {
+		.ar_blockcount = pag->pagf_longest,
+		.ar_startblock = NULLAGBLOCK,
+	};
+	int			error = 0;
+
+	do {
+		struct xfs_busy_extents	*extents;
+
+		extents = kzalloc(sizeof(*extents), GFP_KERNEL);
+		if (!extents) {
+			error = -ENOMEM;
+			break;
+		}
+
+		extents->mount = pag->pag_mount;
+		extents->owner = extents;
+		INIT_LIST_HEAD(&extents->extent_list);
+
+		error = xfs_trim_gather_extents(pag, start, end, minlen,
+				&tcur, extents, blocks_trimmed);
+		if (error) {
+			kfree(extents);
+			break;
+		}
+
+		/*
+		 * We hand the extent list to the discard function here so the
+		 * discarded extents can be removed from the busy extent list.
+		 * This allows the discards to run asynchronously with gathering
+		 * the next round of extents to discard.
+		 *
+		 * However, we must ensure that we do not reference the extent
+		 * list  after this function call, as it may have been freed by
+		 * the time control returns to us.
+		 */
+		error = xfs_discard_extents(pag->pag_mount, extents);
+		if (error)
+			break;
+
+		if (xfs_trim_should_stop())
+			break;
+
+	} while (tcur.ar_blockcount != 0);
+
+	return error;
+
+}
+
+/*
+ * trim a range of the filesystem.
+ *
+ * Note: the parameters passed from userspace are byte ranges into the
+ * filesystem which does not match to the format we use for filesystem block
+ * addressing. FSB addressing is sparse (AGNO|AGBNO), while the incoming format
+ * is a linear address range. Hence we need to use DADDR based conversions and
+ * comparisons for determining the correct offset and regions to trim.
+ */
+int
+xfs_ioc_trim(
+	struct xfs_mount		*mp,
+	struct fstrim_range __user	*urange)
+{
+	struct xfs_perag	*pag;
+	unsigned int		granularity =
+		bdev_discard_granularity(mp->m_ddev_targp->bt_bdev);
+	struct fstrim_range	range;
+	xfs_daddr_t		start, end, minlen;
+	xfs_agnumber_t		agno;
+	uint64_t		blocks_trimmed = 0;
+	int			error, last_error = 0;
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+	if (!bdev_max_discard_sectors(mp->m_ddev_targp->bt_bdev))
+		return -EOPNOTSUPP;
+
+	/*
+	 * We haven't recovered the log, so we cannot use our bnobt-guided
+	 * storage zapping commands.
+	 */
+	if (xfs_has_norecovery(mp))
+		return -EROFS;
+
+	if (copy_from_user(&range, urange, sizeof(range)))
+		return -EFAULT;
+
+	range.minlen = max_t(u64, granularity, range.minlen);
+	minlen = BTOBB(range.minlen);
+	/*
+	 * Truncating down the len isn't actually quite correct, but using
+	 * BBTOB would mean we trivially get overflows for values
+	 * of ULLONG_MAX or slightly lower.  And ULLONG_MAX is the default
+	 * used by the fstrim application.  In the end it really doesn't
+	 * matter as trimming blocks is an advisory interface.
+	 */
+	if (range.start >= XFS_FSB_TO_B(mp, mp->m_sb.sb_dblocks) ||
+	    range.minlen > XFS_FSB_TO_B(mp, mp->m_ag_max_usable) ||
+	    range.len < mp->m_sb.sb_blocksize)
+		return -EINVAL;
+
+	start = BTOBB(range.start);
+	end = start + BTOBBT(range.len) - 1;
+
+	if (end > XFS_FSB_TO_BB(mp, mp->m_sb.sb_dblocks) - 1)
+		end = XFS_FSB_TO_BB(mp, mp->m_sb.sb_dblocks) - 1;
+
+	agno = xfs_daddr_to_agno(mp, start);
+	for_each_perag_range(mp, agno, xfs_daddr_to_agno(mp, end), pag) {
+		error = xfs_trim_extents(pag, start, end, minlen,
+					  &blocks_trimmed);
+		if (error)
+			last_error = error;
+
+		if (xfs_trim_should_stop()) {
+			xfs_perag_rele(pag);
+			break;
+		}
+	}
+
+	if (last_error)
+		return last_error;
+
+	range.len = XFS_FSB_TO_B(mp, blocks_trimmed);
+	if (copy_to_user(urange, &range, sizeof(range)))
+		return -EFAULT;
+	return 0;
+}