On Thu 30-11-17 14:15:58, Andrew Morton wrote: > From: Maxim Patlasov <MPatlasov@xxxxxxxxxxxxx> > Subject: mm: add strictlimit knob > > The "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. In principle I have nothing against this and the usecase sounds reasonable (in fact I believe the lack of a feature like this is one of reasons why desktop automounters usually mount USB devices with 'sync' mount option). So feel free to add: Reviewed-by: Jan Kara <jack@xxxxxxx> Honza > Signed-off-by: Maxim Patlasov <MPatlasov@xxxxxxxxxxxxx> > Cc: Henrique de Moraes Holschuh <hmh@xxxxxxxxxx> > Cc: Theodore Ts'o <tytso@xxxxxxx> > Cc: "Artem S. Tashkinov" <t.artem@xxxxxxxxx> > Cc: Mel Gorman <mel@xxxxxxxxx> > Cc: Jan Kara <jack@xxxxxxx> > Cc: Wu Fengguang <fengguang.wu@xxxxxxxxx> > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > --- > > Documentation/ABI/testing/sysfs-class-bdi | 8 ++++ > mm/backing-dev.c | 35 ++++++++++++++++++++ > 2 files changed, 43 insertions(+) > > diff -puN Documentation/ABI/testing/sysfs-class-bdi~mm-add-strictlimit-knob-v2 Documentation/ABI/testing/sysfs-class-bdi > --- a/Documentation/ABI/testing/sysfs-class-bdi~mm-add-strictlimit-knob-v2 > +++ a/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 -puN mm/backing-dev.c~mm-add-strictlimit-knob-v2 mm/backing-dev.c > --- a/mm/backing-dev.c~mm-add-strictlimit-knob-v2 > +++ a/mm/backing-dev.c > @@ -218,11 +218,46 @@ static ssize_t stable_pages_required_sho > } > 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); > _ -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
