The patch titled Subject: mm/damon/vaddr: fix issue in damon_va_evenly_split_region() has been added to the -mm mm-unstable branch. Its filename is mm-damon-vaddr-fix-issue-in-damon_va_evenly_split_region.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

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: Zheng Yejian zhengyejian@huaweicloud.com Subject: mm/damon/vaddr: fix issue in damon_va_evenly_split_region() Date: Tue, 22 Oct 2024 16:39:26 +0800

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.c... Link: https://lkml.kernel.org/r/20241022083927.3592237-2-zhengyejian@huaweicloud.c... 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 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: Andrew Morton akpm@linux-foundation.org ---

mm/damon/tests/vaddr-kunit.h | 1 + mm/damon/vaddr.c | 4 ++-- 2 files changed, 3 insertions(+), 2 deletions(-)

--- a/mm/damon/tests/vaddr-kunit.h~mm-damon-vaddr-fix-issue-in-damon_va_evenly_split_region +++ a/mm/damon/tests/vaddr-kunit.h @@ -300,6 +300,7 @@ static void damon_test_split_evenly(stru 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); }

--- a/mm/damon/vaddr.c~mm-damon-vaddr-fix-issue-in-damon_va_evenly_split_region +++ a/mm/damon/vaddr.c @@ -67,6 +67,7 @@ static int damon_va_evenly_split_region( 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(

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; _

Patches currently in -mm which might be from zhengyejian@huaweicloud.com are

mm-damon-vaddr-fix-issue-in-damon_va_evenly_split_region.patch mm-damon-vaddr-add-nr_piece-==-1-check-in-damon_va_evenly_split_region.patch