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Message-ID: <F54782D6-65A3-4D35-AE03-8ADE636EE258@nvidia.com>
Date: Tue, 19 Aug 2025 12:58:51 -0400
From: Zi Yan <ziy@...dia.com>
To: Andrew Morton <akpm@...ux-foundation.org>,
David Hildenbrand <david@...hat.com>
Cc: Wei Yang <richard.weiyang@...il.com>, wang lian <lianux.mm@...il.com>,
Baolin Wang <baolin.wang@...ux.alibaba.com>, linux-mm@...ck.org,
Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
"Liam R. Howlett" <Liam.Howlett@...cle.com>, Nico Pache <npache@...hat.com>,
Ryan Roberts <ryan.roberts@....com>, Dev Jain <dev.jain@....com>,
Barry Song <baohua@...nel.org>, Vlastimil Babka <vbabka@...e.cz>,
Mike Rapoport <rppt@...nel.org>, Suren Baghdasaryan <surenb@...gle.com>,
Michal Hocko <mhocko@...e.com>, Shuah Khan <shuah@...nel.org>,
linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v5 3/5] selftests/mm: reimplement is_backed_by_thp() with
more precise check
On 19 Aug 2025, at 12:50, Zi Yan wrote:
> On 19 Aug 2025, at 4:54, David Hildenbrand wrote:
>
>> On 18.08.25 20:46, Zi Yan wrote:
>>> and rename it to is_backed_by_folio().
>>>
>>> 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;
>>>
>>> if order is greater than 0:
>>> 3. checking kpageflags of the head pfn;
>>> 4. checking kpageflags of all tail pfns.
>>>
>>> pmd_order is added to split_huge_page_test.c and replaces max_order.
>>>
>>> Signed-off-by: Zi Yan <ziy@...dia.com>
>>> Reviewed-by: Wei Yang <richard.weiyang@...il.com>
>>> Reviewed-by: wang lian <lianux.mm@...il.com>
>>> ---
>>> .../selftests/mm/split_huge_page_test.c | 88 ++++++++++++++-----
>>> tools/testing/selftests/mm/vm_util.c | 13 +++
>>> tools/testing/selftests/mm/vm_util.h | 4 +
>>> 3 files changed, 81 insertions(+), 24 deletions(-)
>>>
>>> diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
>>> index 089e146efeab..56d1eaf9a860 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;
>>> #define SPLIT_DEBUGFS "/sys/kernel/debug/split_huge_pages"
>>> #define SMAP_PATH "/proc/self/smaps"
>>> @@ -34,26 +35,66 @@ uint64_t pmd_pagesize;
>>> #define PID_FMT_OFFSET "%d,0x%lx,0x%lx,%d,%d"
>>> #define PATH_FMT "%s,0x%lx,0x%lx,%d"
>>> -#define PFN_MASK ((1UL<<55)-1)
>>> -#define KPF_THP (1UL<<22)
>>> -
>>> -static int is_backed_by_thp(char *vaddr, int pagemap_file, int kpageflags_file)
>>> +static bool 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;
>>
>> Final nit (sorry!) :)
>>
>> const unsigned long nr_pages = 1ul << order;
>>
>> so you can make some of the code below easier to read.
>
> Sure. Will send a fixup.
>
>>
>> Acked-by: David Hildenbrand <david@...hat.com>
>>
> Thanks.
Hi Andrew,
The fixup below replaced 1 << order with nr_pages based on David's
suggestion. Do you mind folding it in?
Thanks.
From c07eb882465b938a70acb84e4cdc5b6598536322 Mon Sep 17 00:00:00 2001
From: Zi Yan <ziy@...dia.com>
Date: Tue, 19 Aug 2025 12:52:13 -0400
Subject: [PATCH] fixup: selftests/mm: use nr_pages instead of 1UL << order.
Signed-off-by: Zi Yan <ziy@...dia.com>
---
tools/testing/selftests/mm/split_huge_page_test.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/tools/testing/selftests/mm/split_huge_page_test.c b/tools/testing/selftests/mm/split_huge_page_test.c
index 56d1eaf9a860..f2882cfab568 100644
--- a/tools/testing/selftests/mm/split_huge_page_test.c
+++ b/tools/testing/selftests/mm/split_huge_page_test.c
@@ -38,6 +38,7 @@ unsigned int pmd_order;
static bool is_backed_by_folio(char *vaddr, int order, int pagemap_fd,
int kpageflags_fd)
{
+ const unsigned long nr_pages = 1UL << order;
unsigned long pfn_head;
uint64_t pfn_flags;
unsigned long pfn;
@@ -63,7 +64,7 @@ static bool is_backed_by_folio(char *vaddr, int order, int pagemap_fd,
if (!(pfn_flags & KPF_THP))
return false;
- pfn_head = pfn & ~((1 << order) - 1);
+ pfn_head = pfn & ~(nr_pages - 1);
if (pageflags_get(pfn_head, kpageflags_fd, &pfn_flags))
goto fail;
@@ -73,7 +74,7 @@ static bool is_backed_by_folio(char *vaddr, int order, int pagemap_fd,
return false;
/* check all tail PFN flags */
- for (i = 1; i < 1UL << order; i++) {
+ for (i = 1; i < nr_pages; i++) {
if (pageflags_get(pfn_head + i, kpageflags_fd, &pfn_flags))
goto fail;
if (!(pfn_flags & (KPF_THP | KPF_COMPOUND_TAIL)))
@@ -84,7 +85,7 @@ static bool is_backed_by_folio(char *vaddr, int order, int pagemap_fd,
* check the PFN after this folio, but if its flags cannot be obtained,
* assume this folio has the expected order
*/
- if (pageflags_get(pfn_head + (1UL << order), kpageflags_fd, &pfn_flags))
+ if (pageflags_get(pfn_head + nr_pages, kpageflags_fd, &pfn_flags))
return true;
/* this folio is bigger than the given order */
--
2.50.1
--
Best Regards,
Yan, Zi
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