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Message-ID: <20131106150515.25906.55017.stgit@dhcp-10-30-17-2.sw.ru>
Date: Wed, 06 Nov 2013 19:05:57 +0400
From: Maxim Patlasov <MPatlasov@...allels.com>
To: akpm@...ux-foundation.org
Cc: karl.kiniger@....ge.com, tytso@....edu,
linux-kernel@...r.kernel.org, t.artem@...os.com,
linux-mm@...ck.org, mgorman@...e.de, jack@...e.cz,
fengguang.wu@...el.com, torvalds@...ux-foundation.org,
mpatlasov@...allels.com
Subject: [PATCH] mm: add strictlimit knob -v2
"strictlimit" feature was introduced to enforce per-bdi dirty limits for
FUSE which sets bdi max_ratio to 1% by default:
http://article.gmane.org/gmane.linux.kernel.mm/105809
However the feature can be useful for other relatively slow or untrusted
BDIs like USB flash drives and DVD+RW. The patch adds a knob to enable the
feature:
echo 1 > /sys/class/bdi/X:Y/strictlimit
Being enabled, the feature enforces bdi max_ratio limit even if global (10%)
dirty limit is not reached. Of course, the effect is not visible until
/sys/class/bdi/X:Y/max_ratio is decreased to some reasonable value.
Changed in v2:
- updated patch description and documentation
Signed-off-by: Maxim Patlasov <MPatlasov@...allels.com>
---
Documentation/ABI/testing/sysfs-class-bdi | 8 +++++++
mm/backing-dev.c | 35 +++++++++++++++++++++++++++++
2 files changed, 43 insertions(+)
diff --git a/Documentation/ABI/testing/sysfs-class-bdi b/Documentation/ABI/testing/sysfs-class-bdi
index d773d56..3187a18 100644
--- a/Documentation/ABI/testing/sysfs-class-bdi
+++ b/Documentation/ABI/testing/sysfs-class-bdi
@@ -53,3 +53,11 @@ 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.
+
+strictlimit (read-write)
+
+ Forces per-BDI checks for the share of given device in the write-back
+ cache even before the global background dirty limit is reached. This
+ is useful in situations where the global limit is much higher than
+ affordable for given relatively slow (or untrusted) device. Turning
+ strictlimit on has no visible effect if max_ratio is equal to 100%.
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index ce682f7..4ee1d64 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -234,11 +234,46 @@ static ssize_t stable_pages_required_show(struct device *dev,
}
static DEVICE_ATTR_RO(stable_pages_required);
+static ssize_t strictlimit_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 val;
+ ssize_t ret;
+
+ ret = kstrtouint(buf, 10, &val);
+ if (ret < 0)
+ return ret;
+
+ switch (val) {
+ case 0:
+ bdi->capabilities &= ~BDI_CAP_STRICTLIMIT;
+ break;
+ case 1:
+ bdi->capabilities |= BDI_CAP_STRICTLIMIT;
+ break;
+ default:
+ return -EINVAL;
+ }
+
+ return count;
+}
+static ssize_t strictlimit_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->capabilities & BDI_CAP_STRICTLIMIT));
+}
+static DEVICE_ATTR_RW(strictlimit);
+
static struct attribute *bdi_dev_attrs[] = {
&dev_attr_read_ahead_kb.attr,
&dev_attr_min_ratio.attr,
&dev_attr_max_ratio.attr,
&dev_attr_stable_pages_required.attr,
+ &dev_attr_strictlimit.attr,
NULL,
};
ATTRIBUTE_GROUPS(bdi_dev);
--
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