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Message-ID: <15c288aa-feab-4d3a-af33-b87481eaffe3@arm.com>
Date: Mon, 27 Nov 2023 10:48:13 +0000
From: Ryan Roberts <ryan.roberts@....com>
To: David Hildenbrand <david@...hat.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 24/11/2023 17:48, David Hildenbrand wrote:
> 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.
Yep no problem. Will fix in next version.
>
>> {
>> 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.
Yes agreed. And also, we explicitly only enable a single THP size at a time so
should only allocate a THP of the expected size. Perhaps we should mark the
whole mmap area with MADV_HUGEPAGE since that will serve as a test that we only
get the smaller size we configured?
>
>> - 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?
Yep will do.
>
> [...]
>
>> + 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.
Err, just want to clarify what you are suggesting. With the current patch you
will see something like:
[INFO] detected PMD-mapped THP size: 2048 KiB
[INFO] detected small-sized THP size: 64 KiB
[INFO] detected small-sized THP size: 128 KiB
...
[INFO] detected small-sized THP size: 1024 KiB
Are you suggesting something like this:
[INFO] detected PMD size: 2048 KiB
[INFO] detected THP size: 64 KiB
[INFO] detected THP size: 128 KiB
...
[INFO] detected THP size: 2048 KiB
>
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