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Message-ID: <ead82cbe-19c9-43ce-9f28-7ced118b130a@redhat.com>
Date: Fri, 24 Nov 2023 18:48:50 +0100
From: David Hildenbrand <david@...hat.com>
To: Ryan Roberts <ryan.roberts@....com>,
Andrew Morton <akpm@...ux-foundation.org>,
Matthew Wilcox <willy@...radead.org>,
Yin Fengwei <fengwei.yin@...el.com>,
Yu Zhao <yuzhao@...gle.com>,
Catalin Marinas <catalin.marinas@....com>,
Anshuman Khandual <anshuman.khandual@....com>,
Yang Shi <shy828301@...il.com>,
"Huang, Ying" <ying.huang@...el.com>, Zi Yan <ziy@...dia.com>,
Luis Chamberlain <mcgrof@...nel.org>,
Itaru Kitayama <itaru.kitayama@...il.com>,
"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
John Hubbard <jhubbard@...dia.com>,
David Rientjes <rientjes@...gle.com>,
Vlastimil Babka <vbabka@...e.cz>,
Hugh Dickins <hughd@...gle.com>,
Kefeng Wang <wangkefeng.wang@...wei.com>
Cc: linux-mm@...ck.org, linux-arm-kernel@...ts.infradead.org,
linux-kernel@...r.kernel.org
Subject: Re: [RESEND PATCH v7 09/10] selftests/mm/cow: Generalize
do_run_with_thp() helper
On 22.11.23 17:29, Ryan Roberts wrote:
> do_run_with_thp() prepares (PMD-sized) THP memory into different states
> before running tests. With the introduction of small-sized THP, we would
> like to reuse this logic to also test those smaller THP sizes. So let's
> add a size parameter which tells the function what size THP it should
> operate on.
>
> A separate commit will utilize this change to add new tests for
> small-sized THP, where available.
>
> Signed-off-by: Ryan Roberts <ryan.roberts@....com>
> ---
> tools/testing/selftests/mm/cow.c | 146 +++++++++++++++++--------------
> 1 file changed, 79 insertions(+), 67 deletions(-)
>
> diff --git a/tools/testing/selftests/mm/cow.c b/tools/testing/selftests/mm/cow.c
> index 7324ce5363c0..d03c453cfd5c 100644
> --- a/tools/testing/selftests/mm/cow.c
> +++ b/tools/testing/selftests/mm/cow.c
> @@ -32,7 +32,7 @@
>
> static size_t pagesize;
> static int pagemap_fd;
> -static size_t thpsize;
> +static size_t pmdsize;
> static int nr_hugetlbsizes;
> static size_t hugetlbsizes[10];
> static int gup_fd;
> @@ -734,14 +734,14 @@ enum thp_run {
> THP_RUN_PARTIAL_SHARED,
> };
>
> -static void do_run_with_thp(test_fn fn, enum thp_run thp_run)
> +static void do_run_with_thp(test_fn fn, enum thp_run thp_run, size_t size)
Nit: can we still call it "thpsize" in this function? That makes it
clearer IMHO and avoids most renaming.
> {
> char *mem, *mmap_mem, *tmp, *mremap_mem = MAP_FAILED;
> - size_t size, mmap_size, mremap_size;
> + size_t mmap_size, mremap_size;
> int ret;
>
> - /* For alignment purposes, we need twice the thp size. */
> - mmap_size = 2 * thpsize;
> + /* For alignment purposes, we need twice the requested size. */
> + mmap_size = 2 * size;
> mmap_mem = mmap(NULL, mmap_size, PROT_READ | PROT_WRITE,
> MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
> if (mmap_mem == MAP_FAILED) {
> @@ -749,36 +749,40 @@ static void do_run_with_thp(test_fn fn, enum thp_run thp_run)
> return;
> }
>
> - /* We need a THP-aligned memory area. */
> - mem = (char *)(((uintptr_t)mmap_mem + thpsize) & ~(thpsize - 1));
> + /* We need to naturally align the memory area. */
> + mem = (char *)(((uintptr_t)mmap_mem + size) & ~(size - 1));
>
> - ret = madvise(mem, thpsize, MADV_HUGEPAGE);
> + ret = madvise(mem, size, MADV_HUGEPAGE);
> if (ret) {
> ksft_test_result_fail("MADV_HUGEPAGE failed\n");
> goto munmap;
> }
>
> /*
> - * Try to populate a THP. Touch the first sub-page and test if we get
> - * another sub-page populated automatically.
> + * Try to populate a THP. Touch the first sub-page and test if
> + * we get the last sub-page populated automatically.
> */
> mem[0] = 0;
> - if (!pagemap_is_populated(pagemap_fd, mem + pagesize)) {
> + if (!pagemap_is_populated(pagemap_fd, mem + size - pagesize)) {
> ksft_test_result_skip("Did not get a THP populated\n");
> goto munmap;
> }
Yes! I have a patch lying around here that does that same. :)
I guess there is no need to set MADV_NOHUGEPAGE on the remainder of the
mmap'ed are:
Assume we want a 64KiB thp. We mmap'ed 128KiB. If we get a reasonably
aligned area, we might populate a 128KiB THP.
But I assume the MADV_HUGEPAGE will in all configurations properly
create a separate 64KiB VMA and we'll never get 128 KiB populated. So
this should work reliably.
> - memset(mem, 0, thpsize);
> + memset(mem, 0, size);
>
> - size = thpsize;
> switch (thp_run) {
> case THP_RUN_PMD:
> case THP_RUN_PMD_SWAPOUT:
> + if (size != pmdsize) {
> + ksft_test_result_fail("test bug: can't PMD-map size\n");
> + goto munmap;
> + }
Maybe rather "assert()" because that's a real BUG in the test?
[...]
> + pmdsize = read_pmd_pagesize();
> + if (pmdsize)
> + ksft_print_msg("[INFO] detected PMD-mapped THP size: %zu KiB\n",
Maybe simply: "detected PMD size". Zes, we read it via the THP
interface, but that shouldn't matter much.
--
Cheers,
David / dhildenb
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