According to the logic of damon_va_evenly_split_region(), currently at
least following split cases would not meet the expectation:
Suppose DAMON_MIN_REGION=0x1000,
Case1: Split [0x0, 0x1100) into 1 pieces, then the result would be
acutually [0x0, 0x1000), but NOT the expected [0x0, 0x1100) !!!
Case2: 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:
1. For the above Case1, the 'end' value of the split 1 piece is
aligned but not updated!!!
2. For the above Case2, more pieces are split out than expected!!!
To fix it, in this patch:
- As for the expect to split 1 piece, just return 0;
- Count for each piece split and make sure no more than 'nr_pieces';
- Add above two cases into damon_test_split_evenly().
BTW, currently when running kunit test, DAMON_MIN_REGION is redefined
as 1, then above ALIGN_DOWN cases may not be test, since every int
value is ALIGN-ed to 1.
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 =================
Fixes: 3f49584b262c ("mm/damon: implement primitives for the virtual memory address spaces")
Signed-off-by: Zheng Yejian <zhengyejian@xxxxxxxxxxxxxxx>
---
mm/damon/tests/vaddr-kunit.h | 2 ++
mm/damon/vaddr.c | 13 +++++++++----
2 files changed, 11 insertions(+), 4 deletions(-)
diff --git a/mm/damon/tests/vaddr-kunit.h b/mm/damon/tests/vaddr-kunit.h
index a339d117150f..b9a03e4e29e5 100644
--- a/mm/damon/tests/vaddr-kunit.h
+++ b/mm/damon/tests/vaddr-kunit.h
@@ -300,6 +300,8 @@ 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, 4, 6, 1);
+ damon_test_split_evenly_succ(test, 0, 3, 2);
damon_test_split_evenly_fail(test, 5, 6, 2);
}
diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c
index 08cfd22b5249..1f3cebd20829 100644
--- a/mm/damon/vaddr.c
+++ b/mm/damon/vaddr.c
@@ -67,10 +67,14 @@ 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;
+ int i;
if (!r || !nr_pieces)
return -EINVAL;
+ if (nr_pieces == 1)
+ return 0;
+
orig_end = r->ar.end;
sz_orig = damon_sz_region(r);
sz_piece = ALIGN_DOWN(sz_orig / nr_pieces, DAMON_MIN_REGION);
@@ -79,9 +83,11 @@ static int damon_va_evenly_split_region(struct damon_target *t,
return -EINVAL;
r->ar.end = r->ar.start + sz_piece;
+ /* origin region will be updated as the first one after splitting */
+ i = 1;
+ n = r;
next = damon_next_region(r);
- for (start = r->ar.end; start + sz_piece <= orig_end;
- start += sz_piece) {
+ for (start = r->ar.end; i < nr_pieces; start += sz_piece, i++) {
n = damon_new_region(start, start + sz_piece);
if (!n)
return -ENOMEM;
@@ -89,8 +95,7 @@ static int damon_va_evenly_split_region(struct damon_target *t,
r = n;
}
/* complement last region for possible rounding error */
- if (n)
- n->ar.end = orig_end;
+ n->ar.end = orig_end;
return 0;
}
--
2.25.1
