On Fri 18-01-13 17:13:01, Darrick J. Wong wrote:
> 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.
>
> Tested-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
> Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
The patch looks good. You can add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
Honza
> ---
> arch/tile/Kconfig | 6 ------
> block/blk-core.c | 8 +++++---
> fs/ext3/super.c | 1 +
> include/uapi/linux/fs.h | 3 +++
> mm/Kconfig | 13 +++++++++++++
> mm/bounce.c | 48 +++++++++++++++++++++++++++++++++++++++++++----
> mm/page-writeback.c | 4 ++++
> 7 files changed, 70 insertions(+), 13 deletions(-)
>
>
> diff --git a/arch/tile/Kconfig b/arch/tile/Kconfig
> index 875d008..c671fda 100644
> --- a/arch/tile/Kconfig
> +++ b/arch/tile/Kconfig
> @@ -410,12 +410,6 @@ config TILE_USB
> Provides USB host adapter support for the built-in EHCI and OHCI
> interfaces on TILE-Gx chips.
>
> -# USB OHCI needs the bounce pool since tilegx will often have more
> -# than 4GB of memory, but we don't currently use the IOTLB to present
> -# a 32-bit address to OHCI. So we need to use a bounce pool instead.
> -config NEED_BOUNCE_POOL
> - def_bool USB_OHCI_HCD
> -
> source "drivers/pci/hotplug/Kconfig"
>
> endmenu
> diff --git a/block/blk-core.c b/block/blk-core.c
> index c973249..277134c 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -1474,6 +1474,11 @@ void blk_queue_bio(struct request_queue *q, struct bio *bio)
> */
> blk_queue_bounce(q, &bio);
>
> + if (bio_integrity_enabled(bio) && bio_integrity_prep(bio)) {
> + bio_endio(bio, -EIO);
> + return;
> + }
> +
> if (bio->bi_rw & (REQ_FLUSH | REQ_FUA)) {
> spin_lock_irq(q->queue_lock);
> where = ELEVATOR_INSERT_FLUSH;
> @@ -1714,9 +1719,6 @@ generic_make_request_checks(struct bio *bio)
> */
> blk_partition_remap(bio);
>
> - if (bio_integrity_enabled(bio) && bio_integrity_prep(bio))
> - goto end_io;
> -
> if (bio_check_eod(bio, nr_sectors))
> goto end_io;
>
> diff --git a/fs/ext3/super.c b/fs/ext3/super.c
> index 6e50223..4ba2683 100644
> --- a/fs/ext3/super.c
> +++ b/fs/ext3/super.c
> @@ -2065,6 +2065,7 @@ static int ext3_fill_super (struct super_block *sb, void *data, int silent)
> test_opt(sb,DATA_FLAGS) == EXT3_MOUNT_JOURNAL_DATA ? "journal":
> test_opt(sb,DATA_FLAGS) == EXT3_MOUNT_ORDERED_DATA ? "ordered":
> "writeback");
> + sb->s_flags |= MS_SNAP_STABLE;
>
> return 0;
>
> diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
> index 780d4c6..c7fc1e6 100644
> --- a/include/uapi/linux/fs.h
> +++ b/include/uapi/linux/fs.h
> @@ -86,6 +86,9 @@ struct inodes_stat_t {
> #define MS_KERNMOUNT (1<<22) /* this is a kern_mount call */
> #define MS_I_VERSION (1<<23) /* Update inode I_version field */
> #define MS_STRICTATIME (1<<24) /* Always perform atime updates */
> +
> +/* These sb flags are internal to the kernel */
> +#define MS_SNAP_STABLE (1<<27) /* Snapshot pages during writeback, if needed */
> #define MS_NOSEC (1<<28)
> #define MS_BORN (1<<29)
> #define MS_ACTIVE (1<<30)
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 278e3ab..7901d83 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -258,6 +258,19 @@ config BOUNCE
> def_bool y
> depends on BLOCK && MMU && (ZONE_DMA || HIGHMEM)
>
> +# On the 'tile' arch, USB OHCI needs the bounce pool since tilegx will often
> +# have more than 4GB of memory, but we don't currently use the IOTLB to present
> +# a 32-bit address to OHCI. So we need to use a bounce pool instead.
> +#
> +# We also use the bounce pool to provide stable page writes for jbd. jbd
> +# initiates buffer writeback without locking the page or setting PG_writeback,
> +# and fixing that behavior (a second time; jbd2 doesn't have this problem) is
> +# a major rework effort. Instead, use the bounce buffer to snapshot pages
> +# (until jbd goes away). The only jbd user is ext3.
> +config NEED_BOUNCE_POOL
> + bool
> + default y if (TILE && USB_OHCI_HCD) || (BLK_DEV_INTEGRITY && JBD)
> +
> config NR_QUICK
> int
> depends on QUICKLIST
> diff --git a/mm/bounce.c b/mm/bounce.c
> index 0420867..5f89017 100644
> --- a/mm/bounce.c
> +++ b/mm/bounce.c
> @@ -178,8 +178,45 @@ static void bounce_end_io_read_isa(struct bio *bio, int err)
> __bounce_end_io_read(bio, isa_page_pool, err);
> }
>
> +#ifdef CONFIG_NEED_BOUNCE_POOL
> +static int must_snapshot_stable_pages(struct request_queue *q, struct bio *bio)
> +{
> + struct page *page;
> + struct backing_dev_info *bdi;
> + struct address_space *mapping;
> + struct bio_vec *from;
> + int i;
> +
> + if (bio_data_dir(bio) != WRITE)
> + return 0;
> +
> + if (!bdi_cap_stable_pages_required(&q->backing_dev_info))
> + return 0;
> +
> + /*
> + * Based on the first page that has a valid mapping, decide whether or
> + * not we have to employ bounce buffering to guarantee stable pages.
> + */
> + bio_for_each_segment(from, bio, i) {
> + page = from->bv_page;
> + mapping = page_mapping(page);
> + if (!mapping)
> + continue;
> + bdi = mapping->backing_dev_info;
> + return mapping->host->i_sb->s_flags & MS_SNAP_STABLE;
> + }
> +
> + return 0;
> +}
> +#else
> +static int must_snapshot_stable_pages(struct request_queue *q, struct bio *bio)
> +{
> + return 0;
> +}
> +#endif /* CONFIG_NEED_BOUNCE_POOL */
> +
> static void __blk_queue_bounce(struct request_queue *q, struct bio **bio_orig,
> - mempool_t *pool)
> + mempool_t *pool, int force)
> {
> struct page *page;
> struct bio *bio = NULL;
> @@ -192,7 +229,7 @@ static void __blk_queue_bounce(struct request_queue *q, struct bio **bio_orig,
> /*
> * is destination page below bounce pfn?
> */
> - if (page_to_pfn(page) <= queue_bounce_pfn(q))
> + if (page_to_pfn(page) <= queue_bounce_pfn(q) && !force)
> continue;
>
> /*
> @@ -270,6 +307,7 @@ static void __blk_queue_bounce(struct request_queue *q, struct bio **bio_orig,
>
> void blk_queue_bounce(struct request_queue *q, struct bio **bio_orig)
> {
> + int must_bounce;
> mempool_t *pool;
>
> /*
> @@ -278,13 +316,15 @@ void blk_queue_bounce(struct request_queue *q, struct bio **bio_orig)
> if (!bio_has_data(*bio_orig))
> return;
>
> + must_bounce = must_snapshot_stable_pages(q, *bio_orig);
> +
> /*
> * for non-isa bounce case, just check if the bounce pfn is equal
> * to or bigger than the highest pfn in the system -- in that case,
> * don't waste time iterating over bio segments
> */
> if (!(q->bounce_gfp & GFP_DMA)) {
> - if (queue_bounce_pfn(q) >= blk_max_pfn)
> + if (queue_bounce_pfn(q) >= blk_max_pfn && !must_bounce)
> return;
> pool = page_pool;
> } else {
> @@ -295,7 +335,7 @@ void blk_queue_bounce(struct request_queue *q, struct bio **bio_orig)
> /*
> * slow path
> */
> - __blk_queue_bounce(q, bio_orig, pool);
> + __blk_queue_bounce(q, bio_orig, pool, must_bounce);
> }
>
> EXPORT_SYMBOL(blk_queue_bounce);
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index 9c5af4d..75a13f3 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -2305,6 +2305,10 @@ void wait_for_stable_page(struct page *page)
>
> if (!bdi_cap_stable_pages_required(bdi))
> return;
> +#ifdef CONFIG_NEED_BOUNCE_POOL
> + if (mapping->host->i_sb->s_flags & MS_SNAP_STABLE)
> + return;
> +#endif /* CONFIG_NEED_BOUNCE_POOL */
>
> wait_on_page_writeback(page);
> }
>
--
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR
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