block: optionally snapshot page contents to provide stable pages during write

This provides a band-aid to provide stable page writes on jbd without needing to backport the fixed locking and page writeback bit handling schemes of jbd2. The band-aid works by using bounce buffers to snapshot page contents instead of waiting. For those wondering about the ext3 bandage -- fixing the jbd locking (which was done as part of ext4dev years ago) is a lot of surgery, and setting PG_writeback on data pages when we actually hold the page lock dropped ext3 performance by nearly an order of magnitude. If we're going to migrate iscsi and raid to use stable page writes, the complaints about high latency will likely return. We might as well centralize their page snapshotting thing to one place.

Darrick J. Wong committed 13 years ago

Commit ffecfd11 parent 13575ca7 files · +70 −13Browse files

Unified · Split

7 files

arch/tile/Kconfig +0 −6
block/blk-core.c +5 −3
fs/ext3/super.c +1 −0
include/uapi/linux/fs.h +3 −0
mm/Kconfig +13 −0
mm/bounce.c +44 −4
mm/page-writeback.c +4 −0

arch/tile/Kconfig+0−6

@@ -412,12 +412,6 @@ config TILE_USB · 411 unmodified lines
412	412	Provides USB host adapter support for the built-in EHCI and OHCI
413	413	interfaces on TILE-Gx chips.
414	414
415		−# USB OHCI needs the bounce pool since tilegx will often have more
416		−# than 4GB of memory, but we don't currently use the IOTLB to present
417		−# a 32-bit address to OHCI. So we need to use a bounce pool instead.
418		−config NEED_BOUNCE_POOL
419		− def_bool USB_OHCI_HCD
420		−
421	415	source "drivers/pci/hotplug/Kconfig"
422	416
423	417	endmenu

block/blk-core.c+5−3

@@ -1474,6 +1474,11 @@ void blk_queue_bio(struct request_queue q, struct bio bio) · 1473 unmodified lines
1474	1474	*/
1475	1475	blk_queue_bounce(q, &bio);
1476	1476
	1477	+ if (bio_integrity_enabled(bio) && bio_integrity_prep(bio)) {
	1478	+ bio_endio(bio, -EIO);
	1479	+ return;
	1480	+ }
	1481	+
1477	1482	if (bio->bi_rw & (REQ_FLUSH \| REQ_FUA)) {
1478	1483	spin_lock_irq(q->queue_lock);
1479	1484	where = ELEVATOR_INSERT_FLUSH;
@@ -1714,9 +1719,6 @@ generic_make_request_checks(struct bio *bio) · 234 unmodified lines
1714	1719	*/
1715	1720	blk_partition_remap(bio);
1716	1721
1717		− if (bio_integrity_enabled(bio) && bio_integrity_prep(bio))
1718		− goto end_io;
1719		−
1720	1722	if (bio_check_eod(bio, nr_sectors))
1721	1723	goto end_io;
1722	1724

fs/ext3/super.c+1−0

@@ -2065,6 +2065,7 @@ static int ext3_fill_super (struct super_block sb, void data, int silent) · 2064 unmodified lines
2065	2065	test_opt(sb,DATA_FLAGS) == EXT3_MOUNT_JOURNAL_DATA ? "journal":
2066	2066	test_opt(sb,DATA_FLAGS) == EXT3_MOUNT_ORDERED_DATA ? "ordered":
2067	2067	"writeback");
	2068	+ sb->s_flags \|= MS_SNAP_STABLE;
2068	2069
2069	2070	return 0;
2070	2071

include/uapi/linux/fs.h+3−0

@@ -86,6 +86,9 @@ struct inodes_stat_t { · 85 unmodified lines
86	86	#define MS_KERNMOUNT (1<<22) /* this is a kern_mount call */
87	87	#define MS_I_VERSION (1<<23) /* Update inode I_version field */
88	88	#define MS_STRICTATIME (1<<24) /* Always perform atime updates */
	89	+
	90	+/* These sb flags are internal to the kernel */
	91	+#define MS_SNAP_STABLE (1<<27) /* Snapshot pages during writeback, if needed */
89	92	#define MS_NOSEC (1<<28)
90	93	#define MS_BORN (1<<29)
91	94	#define MS_ACTIVE (1<<30)

mm/Kconfig+13−0

@@ -258,6 +258,19 @@ config BOUNCE · 257 unmodified lines
258	258	def_bool y
259	259	depends on BLOCK && MMU && (ZONE_DMA \|\| HIGHMEM)
260	260
	261	+# On the 'tile' arch, USB OHCI needs the bounce pool since tilegx will often
	262	+# have more than 4GB of memory, but we don't currently use the IOTLB to present
	263	+# a 32-bit address to OHCI. So we need to use a bounce pool instead.
	264	+#
	265	+# We also use the bounce pool to provide stable page writes for jbd. jbd
	266	+# initiates buffer writeback without locking the page or setting PG_writeback,
	267	+# and fixing that behavior (a second time; jbd2 doesn't have this problem) is
	268	+# a major rework effort. Instead, use the bounce buffer to snapshot pages
	269	+# (until jbd goes away). The only jbd user is ext3.
	270	+config NEED_BOUNCE_POOL
	271	+ bool
	272	+ default y if (TILE && USB_OHCI_HCD) \|\| (BLK_DEV_INTEGRITY && JBD)
	273	+
261	274	config NR_QUICK
262	275	int
263	276	depends on QUICKLIST

mm/bounce.c+44−4

@@ -178,8 +178,45 @@ static void bounce_end_io_read_isa(struct bio *bio, int err) · 177 unmodified lines
178	178	__bounce_end_io_read(bio, isa_page_pool, err);
179	179	}
180	180
	181	+#ifdef CONFIG_NEED_BOUNCE_POOL
	182	+static int must_snapshot_stable_pages(struct request_queue q, struct bio bio)
	183	+{
	184	+ struct page *page;
	185	+ struct backing_dev_info *bdi;
	186	+ struct address_space *mapping;
	187	+ struct bio_vec *from;
	188	+ int i;
	189	+
	190	+ if (bio_data_dir(bio) != WRITE)
	191	+ return 0;
	192	+
	193	+ if (!bdi_cap_stable_pages_required(&q->backing_dev_info))
	194	+ return 0;
	195	+
	196	+ /*
	197	+ * Based on the first page that has a valid mapping, decide whether or
	198	+ * not we have to employ bounce buffering to guarantee stable pages.
	199	+ */
	200	+ bio_for_each_segment(from, bio, i) {
	201	+ page = from->bv_page;
	202	+ mapping = page_mapping(page);
	203	+ if (!mapping)
	204	+ continue;
	205	+ bdi = mapping->backing_dev_info;
	206	+ return mapping->host->i_sb->s_flags & MS_SNAP_STABLE;
	207	+ }
	208	+
	209	+ return 0;
	210	+}
	211	+#else
	212	+static int must_snapshot_stable_pages(struct request_queue q, struct bio bio)
	213	+{
	214	+ return 0;
	215	+}
	216	+#endif /* CONFIG_NEED_BOUNCE_POOL */
	217	+
181	218	static void __blk_queue_bounce(struct request_queue q, struct bio *bio_orig,
182		− mempool_t *pool)
	219	+ mempool_t *pool, int force)
183	220	{
184	221	struct page *page;
185	222	struct bio *bio = NULL;
@@ -192,7 +229,7 @@ static void __blk_queue_bounce(struct request_queue q, struct bio *bio_orig, · 6 unmodified lines
192	229	/*
193	230	* is destination page below bounce pfn?
194	231	*/
195		− if (page_to_pfn(page) <= queue_bounce_pfn(q))
	232	+ if (page_to_pfn(page) <= queue_bounce_pfn(q) && !force)
196	233	continue;
197	234
198	235	/*
@@ -270,6 +307,7 @@ static void __blk_queue_bounce(struct request_queue q, struct bio *bio_orig, · 71 unmodified lines
270	307
271	308	void blk_queue_bounce(struct request_queue q, struct bio *bio_orig)
272	309	{
	310	+ int must_bounce;
273	311	mempool_t *pool;
274	312
275	313	/*
@@ -278,13 +316,15 @@ void blk_queue_bounce(struct request_queue q, struct bio *bio_orig) · 2 unmodified lines
278	316	if (!bio_has_data(*bio_orig))
279	317	return;
280	318
	319	+ must_bounce = must_snapshot_stable_pages(q, *bio_orig);
	320	+
281	321	/*
282	322	* for non-isa bounce case, just check if the bounce pfn is equal
283	323	* to or bigger than the highest pfn in the system -- in that case,
284	324	* don't waste time iterating over bio segments
285	325	*/
286	326	if (!(q->bounce_gfp & GFP_DMA)) {
287		− if (queue_bounce_pfn(q) >= blk_max_pfn)
	327	+ if (queue_bounce_pfn(q) >= blk_max_pfn && !must_bounce)
288	328	return;
289	329	pool = page_pool;
290	330	} else {
@@ -295,7 +335,7 @@ void blk_queue_bounce(struct request_queue q, struct bio *bio_orig) · 4 unmodified lines
295	335	/*
296	336	* slow path
297	337	*/
298		− __blk_queue_bounce(q, bio_orig, pool);
	338	+ __blk_queue_bounce(q, bio_orig, pool, must_bounce);
299	339	}
300	340
301	341	EXPORT_SYMBOL(blk_queue_bounce);

mm/page-writeback.c+4−0

@@ -2306,6 +2306,10 @@ void wait_for_stable_page(struct page *page) · 2305 unmodified lines
2306	2306
2307	2307	if (!bdi_cap_stable_pages_required(bdi))
2308	2308	return;
	2309	+#ifdef CONFIG_NEED_BOUNCE_POOL
	2310	+ if (mapping->host->i_sb->s_flags & MS_SNAP_STABLE)
	2311	+ return;
	2312	+#endif /* CONFIG_NEED_BOUNCE_POOL */
2309	2313
2310	2314	wait_on_page_writeback(page);
2311	2315	}