The patch titled
Subject: mm/page-writeback: fix dirty_ratelimit calculation
has been removed from the -mm tree. Its filename was
mm-page-writeback-fix-dirty_ratelimit-calculation.patch
This patch was dropped because it was merged into mainline or a subsystem tree
------------------------------------------------------
From: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Subject: mm/page-writeback: fix dirty_ratelimit calculation
Calculation of dirty_ratelimit sometimes is not correct.
E.g. initial values of dirty_ratelimit == INIT_BW and step == 0,
lead to the following result:
UBSAN: Undefined behaviour in ../mm/page-writeback.c:1286:7
shift exponent 25600 is too large for 64-bit type 'long unsigned int'
The fix is straightforward - make step 0 if the shift exponent is too big.
Signed-off-by: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Cc: Wu Fengguang <fengguang.wu@xxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Andy Shevchenko <andy.shevchenko@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page-writeback.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)
diff -puN mm/page-writeback.c~mm-page-writeback-fix-dirty_ratelimit-calculation mm/page-writeback.c
--- a/mm/page-writeback.c~mm-page-writeback-fix-dirty_ratelimit-calculation
+++ a/mm/page-writeback.c
@@ -1169,6 +1169,7 @@ static void wb_update_dirty_ratelimit(st
unsigned long balanced_dirty_ratelimit;
unsigned long step;
unsigned long x;
+ unsigned long shift;
/*
* The dirty rate will match the writeout rate in long term, except
@@ -1293,11 +1294,11 @@ static void wb_update_dirty_ratelimit(st
* rate itself is constantly fluctuating. So decrease the track speed
* when it gets close to the target. Helps eliminate pointless tremors.
*/
- step >>= dirty_ratelimit / (2 * step + 1);
- /*
- * Limit the tracking speed to avoid overshooting.
- */
- step = (step + 7) / 8;
+ shift = dirty_ratelimit / (2 * step + 1);
+ if (shift < BITS_PER_LONG)
+ step = DIV_ROUND_UP(step >> shift, 8);
+ else
+ step = 0;
if (dirty_ratelimit < balanced_dirty_ratelimit)
dirty_ratelimit += step;
_
Patches currently in -mm which might be from aryabinin@xxxxxxxxxxxxx are
mm-move-max_map_count-bits-into-mmh.patch
mm-dedupclicate-memory-overcommitment-code.patch
ubsan-fix-tree-wide-wmaybe-uninitialized-false-positives.patch
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