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Date: Thu, 1 Nov 2012 14:31:52 +0100
From: Jan Kara <jack@...e.cz>
To: "Darrick J. Wong" <darrick.wong@...cle.com>
Cc: axboe@...nel.dk, lucho@...kov.net, tytso@....edu, sage@...tank.com,
ericvh@...il.com, mfasheh@...e.com, dedekind1@...il.com,
adrian.hunter@...el.com, dhowells@...hat.com, sfrench@...ba.org,
jlbec@...lplan.org, rminnich@...dia.gov,
linux-cifs@...r.kernel.org, jack@...e.cz,
martin.petersen@...cle.com, neilb@...e.de, david@...morbit.com,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
linux-mtd@...ts.infradead.org, bharrosh@...asas.com,
linux-fsdevel@...r.kernel.org,
v9fs-developer@...ts.sourceforge.net, ceph-devel@...r.kernel.org,
linux-ext4@...r.kernel.org, linux-afs@...ts.infradead.org,
ocfs2-devel@....oracle.com
Subject: Re: [PATCH 1/3] bdi: Track users that require stable page writes
On Thu 01-11-12 00:58:13, Darrick J. Wong wrote:
> This creates a per-backing-device counter that tracks the number of users which
> require pages to be held immutable during writeout. Eventually it will be used
> to waive wait_for_page_writeback() if nobody requires stable pages.
As I wrote in another mail, maybe a combination of bdi and sb flag would
make things simpler (less chances for errors). But I can live with this as
well...
Honza
>
> Signed-off-by: Darrick J. Wong <darrick.wong@...cle.com>
> ---
> Documentation/ABI/testing/sysfs-class-bdi | 7 +++++
> block/blk-integrity.c | 4 +++
> include/linux/backing-dev.h | 16 ++++++++++++
> include/linux/blkdev.h | 10 ++++++++
> mm/backing-dev.c | 38 +++++++++++++++++++++++++++++
> 5 files changed, 75 insertions(+)
>
>
> diff --git a/Documentation/ABI/testing/sysfs-class-bdi b/Documentation/ABI/testing/sysfs-class-bdi
> index 5f50097..218a618 100644
> --- a/Documentation/ABI/testing/sysfs-class-bdi
> +++ b/Documentation/ABI/testing/sysfs-class-bdi
> @@ -48,3 +48,10 @@ max_ratio (read-write)
> most of the write-back cache. For example in case of an NFS
> mount that is prone to get stuck, or a FUSE mount which cannot
> be trusted to play fair.
> +
> +stable_pages_required (read-write)
> +
> + If set, the backing device requires that all pages comprising a write
> + request must not be changed until writeout is complete. The system
> + administrator can turn this on if the hardware does not do so already.
> + However, once enabled, this flag cannot be disabled.
> diff --git a/block/blk-integrity.c b/block/blk-integrity.c
> index da2a818..cf2dd95 100644
> --- a/block/blk-integrity.c
> +++ b/block/blk-integrity.c
> @@ -420,6 +420,8 @@ int blk_integrity_register(struct gendisk *disk, struct blk_integrity *template)
> } else
> bi->name = bi_unsupported_name;
>
> + queue_require_stable_pages(disk->queue);
> +
> return 0;
> }
> EXPORT_SYMBOL(blk_integrity_register);
> @@ -438,6 +440,8 @@ void blk_integrity_unregister(struct gendisk *disk)
> if (!disk || !disk->integrity)
> return;
>
> + queue_unrequire_stable_pages(disk->queue);
> +
> bi = disk->integrity;
>
> kobject_uevent(&bi->kobj, KOBJ_REMOVE);
> diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
> index 2a9a9ab..0554f5d 100644
> --- a/include/linux/backing-dev.h
> +++ b/include/linux/backing-dev.h
> @@ -109,6 +109,7 @@ struct backing_dev_info {
> struct dentry *debug_dir;
> struct dentry *debug_stats;
> #endif
> + atomic_t stable_page_users;
> };
>
> int bdi_init(struct backing_dev_info *bdi);
> @@ -307,6 +308,21 @@ long wait_iff_congested(struct zone *zone, int sync, long timeout);
> int pdflush_proc_obsolete(struct ctl_table *table, int write,
> void __user *buffer, size_t *lenp, loff_t *ppos);
>
> +static inline void bdi_require_stable_pages(struct backing_dev_info *bdi)
> +{
> + atomic_inc(&bdi->stable_page_users);
> +}
> +
> +static inline void bdi_unrequire_stable_pages(struct backing_dev_info *bdi)
> +{
> + atomic_dec(&bdi->stable_page_users);
> +}
> +
> +static inline bool bdi_cap_stable_pages_required(struct backing_dev_info *bdi)
> +{
> + return atomic_read(&bdi->stable_page_users) > 0;
> +}
> +
> static inline bool bdi_cap_writeback_dirty(struct backing_dev_info *bdi)
> {
> return !(bdi->capabilities & BDI_CAP_NO_WRITEBACK);
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index 1756001..bf927c0 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -458,6 +458,16 @@ struct request_queue {
> (1 << QUEUE_FLAG_SAME_COMP) | \
> (1 << QUEUE_FLAG_ADD_RANDOM))
>
> +static inline void queue_require_stable_pages(struct request_queue *q)
> +{
> + bdi_require_stable_pages(&q->backing_dev_info);
> +}
> +
> +static inline void queue_unrequire_stable_pages(struct request_queue *q)
> +{
> + bdi_unrequire_stable_pages(&q->backing_dev_info);
> +}
> +
> static inline void queue_lockdep_assert_held(struct request_queue *q)
> {
> if (q->queue_lock)
> diff --git a/mm/backing-dev.c b/mm/backing-dev.c
> index d3ca2b3..dd9f5ed 100644
> --- a/mm/backing-dev.c
> +++ b/mm/backing-dev.c
> @@ -221,12 +221,48 @@ static ssize_t max_ratio_store(struct device *dev,
> }
> BDI_SHOW(max_ratio, bdi->max_ratio)
>
> +static ssize_t stable_pages_required_store(struct device *dev,
> + struct device_attribute *attr,
> + const char *buf, size_t count)
> +{
> + struct backing_dev_info *bdi = dev_get_drvdata(dev);
> + unsigned int spw;
> + ssize_t ret;
> +
> + ret = kstrtouint(buf, 10, &spw);
> + if (ret < 0)
> + return ret;
> +
> + /*
> + * SPW could be enabled due to hw requirement, so don't
> + * let users disable it.
> + */
> + if (bdi_cap_stable_pages_required(bdi) && spw == 0)
> + return -EINVAL;
> +
> + if (spw != 0)
> + atomic_inc(&bdi->stable_page_users);
> +
> + return count;
> +}
> +
> +static ssize_t stable_pages_required_show(struct device *dev,
> + struct device_attribute *attr,
> + char *page)
> +{
> + struct backing_dev_info *bdi = dev_get_drvdata(dev);
> +
> + return snprintf(page, PAGE_SIZE-1, "%d\n",
> + bdi_cap_stable_pages_required(bdi) ? 1 : 0);
> +}
> +
> #define __ATTR_RW(attr) __ATTR(attr, 0644, attr##_show, attr##_store)
>
> static struct device_attribute bdi_dev_attrs[] = {
> __ATTR_RW(read_ahead_kb),
> __ATTR_RW(min_ratio),
> __ATTR_RW(max_ratio),
> + __ATTR_RW(stable_pages_required),
> __ATTR_NULL,
> };
>
> @@ -650,6 +686,8 @@ int bdi_init(struct backing_dev_info *bdi)
> bdi->write_bandwidth = INIT_BW;
> bdi->avg_write_bandwidth = INIT_BW;
>
> + atomic_set(&bdi->stable_page_users, 0);
> +
> err = fprop_local_init_percpu(&bdi->completions);
>
> if (err) {
>
> --
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--
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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