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Thu, 14 Aug 2025 22:41:07 -0700 (PDT) Content-Type: text/plain; charset=us-ascii Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3826.600.51.1.1\)) Subject: Re: [PATCH v4 3/5] selftests/mm: reimplement is_backed_by_thp() with more precise check From: wang lian In-Reply-To: <20250815023915.1394655-4-ziy@nvidia.com> Date: Fri, 15 Aug 2025 13:40:47 +0800 Cc: Wei Yang , Baolin Wang , David Hildenbrand , linux-mm@kvack.org, Andrew Morton , Lorenzo Stoakes , "Liam R. Howlett" , Nico Pache , Ryan Roberts , Dev Jain , Barry Song , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Shuah Khan , linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, wang lian Content-Transfer-Encoding: quoted-printable Message-Id: <89F0947A-3956-4D10-B78A-2AA426B8BEE1@gmail.com> References: <20250815023915.1394655-1-ziy@nvidia.com> <20250815023915.1394655-4-ziy@nvidia.com> To: Zi Yan X-Mailer: Apple Mail (2.3826.600.51.1.1) > On Aug 15, 2025, at 10:39, Zi Yan wrote: >=20 > and rename it to is_backed_by_folio(). >=20 > is_backed_by_folio() checks if the given vaddr is backed a folio with > a given order. It does so by: > 1. getting the pfn of the vaddr; > 2. checking kpageflags of the pfn; >=20 > if order is greater than 0: > 3. checking kpageflags of the head pfn; > 4. checking kpageflags of all tail pfns. >=20 > pmd_order is added to split_huge_page_test.c and replaces max_order. >=20 > Signed-off-by: Zi Yan > --- > .../selftests/mm/split_huge_page_test.c | 90 ++++++++++++++----- > tools/testing/selftests/mm/vm_util.c | 13 +++ > tools/testing/selftests/mm/vm_util.h | 4 + > 3 files changed, 84 insertions(+), 23 deletions(-) >=20 > diff --git a/tools/testing/selftests/mm/split_huge_page_test.c = b/tools/testing/selftests/mm/split_huge_page_test.c > index 89d3dc08fe4c..80f718ca21c7 100644 > --- a/tools/testing/selftests/mm/split_huge_page_test.c > +++ b/tools/testing/selftests/mm/split_huge_page_test.c > @@ -25,6 +25,7 @@ > uint64_t pagesize; > unsigned int pageshift; > uint64_t pmd_pagesize; > +unsigned int pmd_order; >=20 > #define SPLIT_DEBUGFS "/sys/kernel/debug/split_huge_pages" > #define SMAP_PATH "/proc/self/smaps" > @@ -34,27 +35,71 @@ uint64_t pmd_pagesize; > #define PID_FMT_OFFSET "%d,0x%lx,0x%lx,%d,%d" > #define PATH_FMT "%s,0x%lx,0x%lx,%d" >=20 > -#define PFN_MASK ((1UL<<55)-1) > -#define KPF_THP (1UL<<22) > #define GET_ORDER(nr_pages) (31 - __builtin_clz(nr_pages)) >=20 > -static int is_backed_by_thp(char *vaddr, int pagemap_file, int = kpageflags_file) > +static int is_backed_by_folio(char *vaddr, int order, int pagemap_fd, > + int kpageflags_fd) > { > - uint64_t paddr; > - uint64_t page_flags; > + unsigned long pfn_head; > + uint64_t pfn_flags; > + unsigned long pfn; > + unsigned long i; >=20 > - if (pagemap_file) { > - pread(pagemap_file, &paddr, sizeof(paddr), > - ((long)vaddr >> pageshift) * sizeof(paddr)); > + if (pagemap_fd =3D=3D -1 || kpageflags_fd =3D=3D -1) > + goto fail; >=20 > - if (kpageflags_file) { > - pread(kpageflags_file, &page_flags, = sizeof(page_flags), > - (paddr & PFN_MASK) * = sizeof(page_flags)); > + pfn =3D pagemap_get_pfn(pagemap_fd, vaddr); >=20 > - return !!(page_flags & KPF_THP); > - } > + /* non present page */ > + if (pfn =3D=3D -1UL) > + return 0; > + > + if (get_pfn_flags(pfn, kpageflags_fd, &pfn_flags)) > + goto fail; > + > + /* check for order-0 pages */ > + if (!order) { > + if (pfn_flags & (KPF_THP | KPF_COMPOUND_HEAD | = KPF_COMPOUND_TAIL)) > + return 0; > + return 1; > } > - return 0; > + > + /* non THP folio */ > + if (!(pfn_flags & KPF_THP)) > + return 0; > + > + pfn_head =3D pfn & ~((1 << order) - 1); > + > + if (get_pfn_flags(pfn_head, kpageflags_fd, &pfn_flags)) > + goto fail; > + > + /* head PFN has no compound_head flag set */ > + if (!(pfn_flags & (KPF_THP | KPF_COMPOUND_HEAD))) > + return 0; > + > + /* check all tail PFN flags */ > + for (i =3D 1; i < 1UL << order; i++) { > + if (get_pfn_flags(pfn_head + i, kpageflags_fd, = &pfn_flags)) > + goto fail; > + if (!(pfn_flags & (KPF_THP | KPF_COMPOUND_TAIL))) > + return 0; > + } > + > + /* > + * check the PFN after this folio, but if its flags cannot be = obtained, > + * assume this folio has the expected order > + */ > + if (get_pfn_flags(pfn_head + (1UL << order), kpageflags_fd, = &pfn_flags)) > + return 1; > + > + /* this folio is bigger than the given order */ > + if (pfn_flags & (KPF_THP | KPF_COMPOUND_TAIL)) > + return 0; > + > + return 1; > +fail: > + ksft_exit_fail_msg("Failed to get folio info\n"); > + return -1; > } >=20 > static void write_file(const char *path, const char *buf, size_t = buflen) > @@ -235,7 +280,7 @@ static void split_pte_mapped_thp(void) > thp_size =3D 0; > for (i =3D 0; i < pagesize * 4; i++) > if (i % pagesize =3D=3D 0 && > - is_backed_by_thp(&pte_mapped[i], pagemap_fd, = kpageflags_fd)) > + is_backed_by_folio(&pte_mapped[i], pmd_order, = pagemap_fd, kpageflags_fd) =3D=3D 1) > thp_size++; >=20 > if (thp_size !=3D 4) > @@ -252,7 +297,7 @@ static void split_pte_mapped_thp(void) > ksft_exit_fail_msg("%ld byte corrupted\n", i); >=20 > if (i % pagesize =3D=3D 0 && > - is_backed_by_thp(&pte_mapped[i], pagemap_fd, = kpageflags_fd)) > + is_backed_by_folio(&pte_mapped[i], 0, pagemap_fd, = kpageflags_fd) =3D=3D 0) > thp_size++; > } >=20 > @@ -524,7 +569,6 @@ int main(int argc, char **argv) > const char *fs_loc; > bool created_tmp; > int offset; > - unsigned int max_order; > unsigned int nr_pages; > unsigned int tests; >=20 > @@ -545,28 +589,28 @@ int main(int argc, char **argv) > ksft_exit_fail_msg("Reading PMD pagesize failed\n"); >=20 > nr_pages =3D pmd_pagesize / pagesize; > - max_order =3D GET_ORDER(nr_pages); > - tests =3D 2 + (max_order - 1) + (2 * max_order) + (max_order - = 1) * 4 + 2; > + pmd_order =3D GET_ORDER(nr_pages); > + tests =3D 2 + (pmd_order - 1) + (2 * pmd_order) + (pmd_order - = 1) * 4 + 2; > ksft_set_plan(tests); >=20 > fd_size =3D 2 * pmd_pagesize; >=20 > split_pmd_zero_pages(); >=20 > - for (i =3D 0; i < max_order; i++) > + for (i =3D 0; i < pmd_order; i++) > if (i !=3D 1) > split_pmd_thp_to_order(i); >=20 > split_pte_mapped_thp(); > - for (i =3D 0; i < max_order; i++) > + for (i =3D 0; i < pmd_order; i++) > split_file_backed_thp(i); >=20 > created_tmp =3D prepare_thp_fs(optional_xfs_path, = fs_loc_template, > &fs_loc); > - for (i =3D max_order - 1; i >=3D 0; i--) > + for (i =3D pmd_order - 1; i >=3D 0; i--) > split_thp_in_pagecache_to_order_at(fd_size, fs_loc, i, = -1); >=20 > - for (i =3D 0; i < max_order; i++) > + for (i =3D 0; i < pmd_order; i++) > for (offset =3D 0; > offset < nr_pages; > offset +=3D MAX(nr_pages / 4, 1 << i)) > diff --git a/tools/testing/selftests/mm/vm_util.c = b/tools/testing/selftests/mm/vm_util.c > index 6a239aa413e2..18b7cb51fc56 100644 > --- a/tools/testing/selftests/mm/vm_util.c > +++ b/tools/testing/selftests/mm/vm_util.c > @@ -338,6 +338,19 @@ int detect_hugetlb_page_sizes(size_t sizes[], int = max) > return count; > } >=20 > +int get_pfn_flags(unsigned long pfn, int kpageflags_fd, uint64_t = *flags) > +{ > + size_t count; > + > + count =3D pread(kpageflags_fd, flags, sizeof(*flags), > + pfn * sizeof(*flags)); > + > + if (count !=3D sizeof(*flags)) > + return -1; > + > + return 0; > +} > + > /* If `ioctls' non-NULL, the allowed ioctls will be returned into the = var */ > int uffd_register_with_ioctls(int uffd, void *addr, uint64_t len, > bool miss, bool wp, bool minor, uint64_t = *ioctls) > diff --git a/tools/testing/selftests/mm/vm_util.h = b/tools/testing/selftests/mm/vm_util.h > index 1843ad48d32b..03481ca0a1b4 100644 > --- a/tools/testing/selftests/mm/vm_util.h > +++ b/tools/testing/selftests/mm/vm_util.h > @@ -18,6 +18,9 @@ > #define PM_SWAP BIT_ULL(62) > #define PM_PRESENT BIT_ULL(63) >=20 > +#define KPF_COMPOUND_HEAD BIT_ULL(15) > +#define KPF_COMPOUND_TAIL BIT_ULL(16) > +#define KPF_THP BIT_ULL(22) > /* > * Ignore the checkpatch warning, we must read from x but don't want = to do > * anything with it in order to trigger a read page fault. We = therefore must use > @@ -85,6 +88,7 @@ bool check_huge_shmem(void *addr, int nr_hpages, = uint64_t hpage_size); > int64_t allocate_transhuge(void *ptr, int pagemap_fd); > unsigned long default_huge_page_size(void); > int detect_hugetlb_page_sizes(size_t sizes[], int max); > +int get_pfn_flags(unsigned long pfn, int kpageflags_fd, uint64_t = *flags); >=20 > int uffd_register(int uffd, void *addr, uint64_t len, > bool miss, bool wp, bool minor); > --=20 > 2.50.1 LGTM. Reviewed-by: wang lian Best regards, wang lian