The patch titled
Subject: mm: use part per 1000000 for bdi ratios.
has been added to the -mm mm-unstable branch. Its filename is
mm-use-part-per-1000000-for-bdi-ratios.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-use-part-per-1000000-for-bdi-ratios.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Stefan Roesch <shr@xxxxxxxxxxxx>
Subject: mm: use part per 1000000 for bdi ratios.
Date: Fri, 18 Nov 2022 16:51:59 -0800
To get finer granularity for ratio calculations use part per million
instead of percentiles. This is especially important if we want to
automatically convert byte values to ratios. Otherwise the values that
are actually used can be quite different. This is also important for
machines with more main memory (1% of 256GB is already 2.5GB).
Link: https://lkml.kernel.org/r/20221119005215.3052436-5-shr@xxxxxxxxxxxx
Signed-off-by: Stefan Roesch <shr@xxxxxxxxxxxx>
Cc: Chris Mason <clm@xxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/backing-dev.h | 3 +++
mm/backing-dev.c | 6 +++---
mm/page-writeback.c | 15 +++++++++------
3 files changed, 15 insertions(+), 9 deletions(-)
--- a/include/linux/backing-dev.h~mm-use-part-per-1000000-for-bdi-ratios
+++ a/include/linux/backing-dev.h
@@ -102,6 +102,9 @@ static inline unsigned long wb_stat_erro
#endif
}
+/* BDI ratio is expressed as part per 1000000 for finer granularity. */
+#define BDI_RATIO_SCALE 10000
+
int bdi_set_min_ratio(struct backing_dev_info *bdi, unsigned int min_ratio);
int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ratio);
int bdi_set_strict_limit(struct backing_dev_info *bdi, unsigned int strict_limit);
--- a/mm/backing-dev.c~mm-use-part-per-1000000-for-bdi-ratios
+++ a/mm/backing-dev.c
@@ -178,7 +178,7 @@ static ssize_t min_ratio_store(struct de
return ret;
}
-BDI_SHOW(min_ratio, bdi->min_ratio)
+BDI_SHOW(min_ratio, bdi->min_ratio / BDI_RATIO_SCALE)
static ssize_t max_ratio_store(struct device *dev,
struct device_attribute *attr, const char *buf, size_t count)
@@ -197,7 +197,7 @@ static ssize_t max_ratio_store(struct de
return ret;
}
-BDI_SHOW(max_ratio, bdi->max_ratio)
+BDI_SHOW(max_ratio, bdi->max_ratio / BDI_RATIO_SCALE)
static ssize_t stable_pages_required_show(struct device *dev,
struct device_attribute *attr,
@@ -809,7 +809,7 @@ int bdi_init(struct backing_dev_info *bd
kref_init(&bdi->refcnt);
bdi->min_ratio = 0;
- bdi->max_ratio = 100;
+ bdi->max_ratio = 100 * BDI_RATIO_SCALE;
bdi->max_prop_frac = FPROP_FRAC_BASE;
INIT_LIST_HEAD(&bdi->bdi_list);
INIT_LIST_HEAD(&bdi->wb_list);
--- a/mm/page-writeback.c~mm-use-part-per-1000000-for-bdi-ratios
+++ a/mm/page-writeback.c
@@ -197,7 +197,7 @@ static void wb_min_max_ratio(struct bdi_
min *= this_bw;
min = div64_ul(min, tot_bw);
}
- if (max < 100) {
+ if (max < 100 * BDI_RATIO_SCALE) {
max *= this_bw;
max = div64_ul(max, tot_bw);
}
@@ -655,6 +655,8 @@ int bdi_set_min_ratio(struct backing_dev
unsigned int delta;
int ret = 0;
+ min_ratio *= BDI_RATIO_SCALE;
+
spin_lock_bh(&bdi_lock);
if (min_ratio > bdi->max_ratio) {
ret = -EINVAL;
@@ -665,7 +667,7 @@ int bdi_set_min_ratio(struct backing_dev
bdi->min_ratio = min_ratio;
} else {
delta = min_ratio - bdi->min_ratio;
- if (bdi_min_ratio + delta < 100) {
+ if (bdi_min_ratio + delta < 100 * BDI_RATIO_SCALE) {
bdi_min_ratio += delta;
bdi->min_ratio = min_ratio;
} else {
@@ -684,6 +686,7 @@ int bdi_set_max_ratio(struct backing_dev
if (max_ratio > 100)
return -EINVAL;
+ max_ratio *= BDI_RATIO_SCALE;
spin_lock_bh(&bdi_lock);
if (bdi->min_ratio > max_ratio) {
@@ -775,15 +778,15 @@ static unsigned long __wb_calc_thresh(st
fprop_fraction_percpu(&dom->completions, dtc->wb_completions,
&numerator, &denominator);
- wb_thresh = (thresh * (100 - bdi_min_ratio)) / 100;
+ wb_thresh = (thresh * (100 * BDI_RATIO_SCALE - bdi_min_ratio)) / (100 * BDI_RATIO_SCALE);
wb_thresh *= numerator;
wb_thresh = div64_ul(wb_thresh, denominator);
wb_min_max_ratio(dtc->wb, &wb_min_ratio, &wb_max_ratio);
- wb_thresh += (thresh * wb_min_ratio) / 100;
- if (wb_thresh > (thresh * wb_max_ratio) / 100)
- wb_thresh = thresh * wb_max_ratio / 100;
+ wb_thresh += (thresh * wb_min_ratio) / (100 * BDI_RATIO_SCALE);
+ if (wb_thresh > (thresh * wb_max_ratio) / (100 * BDI_RATIO_SCALE))
+ wb_thresh = thresh * wb_max_ratio / (100 * BDI_RATIO_SCALE);
return wb_thresh;
}
_
Patches currently in -mm which might be from shr@xxxxxxxxxxxx are
mm-add-bdi_set_strict_limit-function.patch
mm-add-knob-sys-class-bdi-bdi-strict_limit.patch
mm-document-sys-class-bdi-bdi-strict_limit-knob.patch
mm-use-part-per-1000000-for-bdi-ratios.patch
mm-add-bdi_get_max_bytes-function.patch
mm-split-off-__bdi_set_max_ratio-function.patch
mm-add-bdi_set_max_bytes-function.patch
mm-add-knob-sys-class-bdi-bdi-max_bytes.patch
mm-document-sys-class-bdi-bdi-max_bytes-knob.patch
mm-add-bdi_get_min_bytes-function.patch
mm-split-off-__bdi_set_min_ratio-function.patch
mm-add-bdi_set_min_bytes-function.patch
mm-add-sys-class-bdi-bdi-min_bytes-knob.patch
mm-document-sys-class-bdi-bdi-min_bytes-knob.patch
mm-add-bdi_set_max_ratio_no_scale-function.patch
mm-add-sys-class-bdi-bdi-max_ratio_fine-knob.patch
mm-document-sys-class-bdi-bdi-max_ratio_fine-knob.patch
mm-add-bdi_set_min_ratio_no_scale-function.patch
mm-add-sys-class-bdi-bdi-min_ratio_fine-knob.patch
mm-document-sys-class-bdi-bdi-min_ratio_fine-knob.patch
