| Message ID | 20241022083927.3592237-2-zhengyejian@huaweicloud.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm/damon/vaddr: Fix issue in damon_va_evenly_split_region() | expand |
Hi Zheng, We Cc kunit folks for any DAMON kunit test changes, so I Cc-ed them. On Tue, 22 Oct 2024 16:39:26 +0800 Zheng Yejian <zhengyejian@huaweicloud.com> wrote: > 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: Just for a clarification. damon-operations test doesn't fail without this patch. This patch introduces two changes. A new kunit test, and a bug fix. Without the bug fix, the new kunit test fails. I usually prefer separating test changes from fixes (introduc a fix first, and then the test for it, to avoid unnecessary test failures). But, given the small size and the simplicity of the kunit change for this patch, I think introducing it together with the fix is ok. > > # ./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@huaweicloud.com> Reviewed-by: SeongJae Park <sj@kernel.org> Thanks, SJ [...]
On Tue, 22 Oct 2024 16:39:26 +0800 Zheng Yejian <zhengyejian@huaweicloud.com> wrote: [...] > Fixes: 3f49584b262c ("mm/damon: implement primitives for the virtual memory address spaces") > Signed-off-by: Zheng Yejian <zhengyejian@huaweicloud.com> > --- > > v1 -> v2: > - Move 'nr_pieces == 1' check into separate patch and update commit messages; > - Change type of variable 'i' to be 'unsigned int'; > - Remove a puzzling comment; > > v1: https://lore.kernel.org/all/20241018035304.1050135-1-zhengyejian@huaweicloud.com/ Nit. If the patch series has a cover letter, we usually put this kind of revision history on the cover letter. Thanks, SJ [...]
diff --git a/mm/damon/tests/vaddr-kunit.h b/mm/damon/tests/vaddr-kunit.h index a339d117150f..a149e354bb26 100644 --- a/mm/damon/tests/vaddr-kunit.h +++ b/mm/damon/tests/vaddr-kunit.h @@ -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); } diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c index 08cfd22b5249..dba3b2f4d758 100644 --- a/mm/damon/vaddr.c +++ b/mm/damon/vaddr.c @@ -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;
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 ================= Fixes: 3f49584b262c ("mm/damon: implement primitives for the virtual memory address spaces") Signed-off-by: Zheng Yejian <zhengyejian@huaweicloud.com> --- v1 -> v2: - Move 'nr_pieces == 1' check into separate patch and update commit messages; - Change type of variable 'i' to be 'unsigned int'; - Remove a puzzling comment; v1: https://lore.kernel.org/all/20241018035304.1050135-1-zhengyejian@huaweicloud.com/ mm/damon/tests/vaddr-kunit.h | 1 + mm/damon/vaddr.c | 4 ++-- 2 files changed, 3 insertions(+), 2 deletions(-)