Commit f3c7a1ed authored by Zheng Yejian's avatar Zheng Yejian Committed by Andrew Morton
Browse files

mm/damon/vaddr: fix issue in damon_va_evenly_split_region() 

Patch series "mm/damon/vaddr: Fix issue in
damon_va_evenly_split_region()".  v2.

According to the logic of damon_va_evenly_split_region(), currently
following split case would not meet the expectation:

  Suppose DAMON_MIN_REGION=0x1000,
  Case: Split [0x0, 0x3000) into 2 pieces, then the result would be
        acutually 3 regions:
          [0x0, 0x1000), [0x1000, 0x2000), [0x2000, 0x3000)
        but NOT the expected 2 regions:
          [0x0, 0x1000), [0x1000, 0x3000) !!!

The root cause is that when calculating size of each split piece in
damon_va_evenly_split_region():

  `sz_piece = ALIGN_DOWN(sz_orig / nr_pieces, DAMON_MIN_REGION);`

both the dividing and the ALIGN_DOWN may cause loss of precision, then
each time split one piece of size 'sz_piece' from origin 'start' to 'end'
would cause more pieces are split out than expected!!!

To fix it, count for each piece split and make sure no more than
'nr_pieces'.  In addition, add above case into damon_test_split_evenly().

And add 'nr_piece == 1' check in damon_va_evenly_split_region() for better
code readability and add a corresponding kunit testcase.


This patch (of 2):

According to the logic of damon_va_evenly_split_region(), currently
following split case would not meet the expectation:

  Suppose DAMON_MIN_REGION=0x1000,
  Case: Split [0x0, 0x3000) into 2 pieces, then the result would be
        acutually 3 regions:
          [0x0, 0x1000), [0x1000, 0x2000), [0x2000, 0x3000)
        but NOT the expected 2 regions:
          [0x0, 0x1000), [0x1000, 0x3000) !!!

The root cause is that when calculating size of each split piece in
damon_va_evenly_split_region():

  `sz_piece = ALIGN_DOWN(sz_orig / nr_pieces, DAMON_MIN_REGION);`

both the dividing and the ALIGN_DOWN may cause loss of precision,
then each time split one piece of size 'sz_piece' from origin 'start' to
'end' would cause more pieces are split out than expected!!!

To fix it, count for each piece split and make sure no more than
'nr_pieces'. In addition, add above case into damon_test_split_evenly().

After this patch, damon-operations test passed:

 # ./tools/testing/kunit/kunit.py run damon-operations
 [...]
 ============== damon-operations (6 subtests) ===============
 [PASSED] damon_test_three_regions_in_vmas
 [PASSED] damon_test_apply_three_regions1
 [PASSED] damon_test_apply_three_regions2
 [PASSED] damon_test_apply_three_regions3
 [PASSED] damon_test_apply_three_regions4
 [PASSED] damon_test_split_evenly
 ================ [PASSED] damon-operations =================

Link: https://lkml.kernel.org/r/20241022083927.3592237-1-zhengyejian@huaweicloud.com
Link: https://lkml.kernel.org/r/20241022083927.3592237-2-zhengyejian@huaweicloud.com


Fixes: 3f49584b ("mm/damon: implement primitives for the virtual memory address spaces")
Signed-off-by: default avatarZheng Yejian <zhengyejian@huaweicloud.com>
Reviewed-by: default avatarSeongJae Park <sj@kernel.org>
Cc: Fernand Sieber <sieberf@amazon.com>
Cc: Leonard Foerster <foersleo@amazon.de>
Cc: Shakeel Butt <shakeel.butt@linux.dev>
Cc: Ye Weihua <yeweihua4@huawei.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent ab505e8b

mm/damon/tests/vaddr-kunit.h

+1 −0
Original line number Diff line number Diff line
@@ -300,6 +300,7 @@ static void damon_test_split_evenly(struct kunit *test) 
	damon_test_split_evenly_fail(test, 0, 100, 0);

	damon_test_split_evenly_succ(test, 0, 100, 10);

	damon_test_split_evenly_succ(test, 5, 59, 5);

	damon_test_split_evenly_succ(test, 0, 3, 2);

	damon_test_split_evenly_fail(test, 5, 6, 2);

}

mm/damon/vaddr.c

+2 −2
Original line number Diff line number Diff line
@@ -67,6 +67,7 @@ static int damon_va_evenly_split_region(struct damon_target *t, 
	unsigned long sz_orig, sz_piece, orig_end;

	struct damon_region *n = NULL, *next;

	unsigned long start;

	unsigned int i;



	if (!r || !nr_pieces)

		return -EINVAL;
@@ -80,8 +81,7 @@ static int damon_va_evenly_split_region(struct damon_target *t, 


	r->ar.end = r->ar.start + sz_piece;

	next = damon_next_region(r);

	for (start = r->ar.end; start + sz_piece <= orig_end;

			start += sz_piece) {

	for (start = r->ar.end, i = 1; i < nr_pieces; start += sz_piece, i++) {

		n = damon_new_region(start, start + sz_piece);

		if (!n)

			return -ENOMEM;