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Subject[PATCH 1/4] bdi: Allow block devices to say that they require stable page writes
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This creates a per-backing-device flag that tracks whether or not pages must be
held immutable during writeout. Eventually it will be used to waive
wait_for_page_writeback() if nobody requires stable pages.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
Documentation/ABI/testing/sysfs-class-bdi | 5 +++++
block/blk-integrity.c | 4 ++++
include/linux/backing-dev.h | 6 ++++++
mm/backing-dev.c | 11 +++++++++++
4 files changed, 26 insertions(+)


diff --git a/Documentation/ABI/testing/sysfs-class-bdi b/Documentation/ABI/testing/sysfs-class-bdi
index 5f50097..d773d56 100644
--- a/Documentation/ABI/testing/sysfs-class-bdi
+++ b/Documentation/ABI/testing/sysfs-class-bdi
@@ -48,3 +48,8 @@ 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-only)
+
+ If set, the backing device requires that all pages comprising a write
+ request must not be changed until writeout is complete.
diff --git a/block/blk-integrity.c b/block/blk-integrity.c
index da2a818..dabd221 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;

+ disk->queue->backing_dev_info.capabilities |= BDI_CAP_STABLE_WRITES;
+
return 0;
}
EXPORT_SYMBOL(blk_integrity_register);
@@ -438,6 +440,8 @@ void blk_integrity_unregister(struct gendisk *disk)
if (!disk || !disk->integrity)
return;

+ disk->queue->backing_dev_info.capabilities &= ~BDI_CAP_STABLE_WRITES;
+
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..085501f 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -253,6 +253,7 @@ int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ratio);
#define BDI_CAP_EXEC_MAP 0x00000040
#define BDI_CAP_NO_ACCT_WB 0x00000080
#define BDI_CAP_SWAP_BACKED 0x00000100
+#define BDI_CAP_STABLE_WRITES 0x00000200

#define BDI_CAP_VMFLAGS \
(BDI_CAP_READ_MAP | BDI_CAP_WRITE_MAP | BDI_CAP_EXEC_MAP)
@@ -307,6 +308,11 @@ 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 bool bdi_cap_stable_pages_required(struct backing_dev_info *bdi)
+{
+ return bdi->capabilities & BDI_CAP_STABLE_WRITES;
+}
+
static inline bool bdi_cap_writeback_dirty(struct backing_dev_info *bdi)
{
return !(bdi->capabilities & BDI_CAP_NO_WRITEBACK);
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index d3ca2b3..41733c5 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -221,12 +221,23 @@ static ssize_t max_ratio_store(struct device *dev,
}
BDI_SHOW(max_ratio, bdi->max_ratio)

+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_RO(stable_pages_required),
__ATTR_NULL,
};



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