Re: [RFC PATCH 2/3] mm/mincore: Use can_pte_batch_count() in mincore_pte_range() for pte batch mincore_pte_range()

Re: [RFC PATCH 2/3] mm/mincore: Use can_pte_batch_count() in mincore_pte_range() for pte batch mincore_pte_range()

[zhangqilong]

 On Mon, Oct 27, 2025 at 10:03:14PM +0800, Zhang Qilong wrote:
> > In current mincore_pte_range(), if pte_batch_hint() return one pte,
> > it's not efficient, just call new added can_pte_batch_count().
> >
> > In ARM64 qemu, with 8 CPUs, 32G memory, a simple test demo like:
> > 1. mmap 1G anon memory
> > 2. write 1G data by 4k step
> > 3. mincore the mmaped 1G memory
> > 4. get the time consumed by mincore
> >
> > Tested the following cases:
> >  - 4k, disabled all hugepage setting.
> >  - 64k mTHP, only enable 64k hugepage setting.
> >
> > Before
> >
> > Case status | Consumed time (us)  |
> > ----------------------------------|
> > 4k          | 7356                |
> > 64k mTHP    | 3670                |
> >
> > Pathed:
> >
> > Case status | Consumed time (us)  |
> > ----------------------------------|
> > 4k          | 4419                |
> > 64k mTHP    | 3061                |
> >
> > The result is evident and demonstrate a significant improvement in the
> > pte batch. While verification within a single environment may have
> > inherent randomness. there is a high probability of achieving positive
> > effects.
> 
> Recent batch PTE series seriously regressed non-arm, so I'm afraid we can't
> accept any series that doesn't show statistics for _other platforms_.
> 
> Please make sure you at least test x86-64.

OK, I will have  a  test on x86-64 as soon and it may yield unexpected results.

> 
> This code is very sensitive and we're not going to accept a patch like this without
> _being sure_ it's ok.

Year, it's a hot path, we should be extremely cautious.

> 
> >
> > Signed-off-by: Zhang Qilong <zhangqilong3@huawei.com>
> > ---
> >  mm/mincore.c | 10 +++-------
> >  1 file changed, 3 insertions(+), 7 deletions(-)
> >
> > diff --git a/mm/mincore.c b/mm/mincore.c index
> > 8ec4719370e1..2cc5d276d1cd 100644
> > --- a/mm/mincore.c
> > +++ b/mm/mincore.c
> > @@ -178,18 +178,14 @@ static int mincore_pte_range(pmd_t *pmd,
> unsigned long addr, unsigned long end,
> >  		/* We need to do cache lookup too for pte markers */
> >  		if (pte_none_mostly(pte))
> >  			__mincore_unmapped_range(addr, addr + PAGE_SIZE,
> >  						 vma, vec);
> >  		else if (pte_present(pte)) {
> > -			unsigned int batch = pte_batch_hint(ptep, pte);
> > -
> > -			if (batch > 1) {
> > -				unsigned int max_nr = (end - addr) >>
> PAGE_SHIFT;
> > -
> > -				step = min_t(unsigned int, batch, max_nr);
> > -			}
> > +			unsigned int max_nr = (end - addr) >> PAGE_SHIFT;
> >
> > +			step = can_pte_batch_count(vma, ptep, &pte,
> > +						   max_nr, 0);
> >  			for (i = 0; i < step; i++)
> >  				vec[i] = 1;
> >  		} else { /* pte is a swap entry */
> >  			*vec = mincore_swap(pte_to_swp_entry(pte), false);
> >  		}
> > --
> > 2.43.0
> >

Re: [RFC PATCH 2/3] mm/mincore: Use can_pte_batch_count() in mincore_pte_range() for pte batch mincore_pte_range()

[zhangqilong]

> On 27.10.25 15:03, Zhang Qilong wrote:
> > In current mincore_pte_range(), if pte_batch_hint() return one pte,
> > it's not efficient, just call new added can_pte_batch_count().
> >
> > In ARM64 qemu, with 8 CPUs, 32G memory, a simple test demo like:
> > 1. mmap 1G anon memory
> > 2. write 1G data by 4k step
> > 3. mincore the mmaped 1G memory
> > 4. get the time consumed by mincore
> >
> > Tested the following cases:
> >   - 4k, disabled all hugepage setting.
> >   - 64k mTHP, only enable 64k hugepage setting.
> >
> > Before
> >
> > Case status | Consumed time (us)  |
> > ----------------------------------|
> > 4k          | 7356                |
> > 64k mTHP    | 3670                |
> >
> > Pathed:
> >
> > Case status | Consumed time (us)  |
> > ----------------------------------|
> > 4k          | 4419                |
> > 64k mTHP    | 3061                |
> >
> 
> I assume you're only lucky in that benchmark because you got consecutive 4k
> pages / 64k mTHP from the buddy, right?

Year, the demo case is relatively simple, which may result in stronger continuity
of allocated physical page addresses. 
This case primarily aims to validate optimization effectiveness in contiguous page
address. Maybe we also need watch side effectiveness in non-contiguous page
address.

> 
> So I suspect that this will mostly just make a micro benchmark happy, because
> the reality where we allocate randomly over time, for the PCP, etc will look
> quite different.
> 
> --
> Cheers
> 
> David / dhildenb
> 

[RFC PATCH 0/3] mm: PTEs batch optimization in mincore and mremap

[Zhang Qilong]

This first patch extract a new interface named can_pte_batch_count()
from folio_pte_batch_flags() for pte batch. Thew new interface avoids
folio access, and counts more pte, not just limited to entries mapped
within a single folio. Caller need pass a range within a single VMA
and a single page and it detect consecutive (present) PTEs that map
consecutive pages. The 2th and 3rd patches use can_pte_batch_count()
do pte batch.

Zhang Qilong (3):
  mm: Introduce can_pte_batch_count() for PTEs batch optimization.
  mm/mincore: Use can_pte_batch_count() in mincore_pte_range() for pte
    batch mincore_pte_range()
  mm/mremap: Use can_pte_batch_count() instead of folio_pte_batch() for
    pte batch

 mm/internal.h | 76 +++++++++++++++++++++++++++++++++++++++------------
 mm/mincore.c  | 10 ++-----
 mm/mremap.c   | 16 ++---------
 3 files changed, 64 insertions(+), 38 deletions(-)

-- 
2.43.0

[RFC PATCH 2/3] mm/mincore: Use can_pte_batch_count() in mincore_pte_range() for pte batch mincore_pte_range()

[Zhang Qilong]

In current mincore_pte_range(), if pte_batch_hint() return one
pte, it's not efficient, just call new added can_pte_batch_count().

In ARM64 qemu, with 8 CPUs, 32G memory, a simple test demo like:
1. mmap 1G anon memory
2. write 1G data by 4k step
3. mincore the mmaped 1G memory
4. get the time consumed by mincore

Tested the following cases:
 - 4k, disabled all hugepage setting.
 - 64k mTHP, only enable 64k hugepage setting.

Before

Case status | Consumed time (us)  |
----------------------------------|
4k          | 7356                |
64k mTHP    | 3670                |

Pathed:

Case status | Consumed time (us)  |
----------------------------------|
4k          | 4419                |
64k mTHP    | 3061                |

The result is evident and demonstrate a significant improvement in
the pte batch. While verification within a single environment may
have inherent randomness. there is a high probability of achieving
positive effects.

Signed-off-by: Zhang Qilong <zhangqilong3@huawei.com>
---
 mm/mincore.c | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/mm/mincore.c b/mm/mincore.c
index 8ec4719370e1..2cc5d276d1cd 100644
--- a/mm/mincore.c
+++ b/mm/mincore.c
@@ -178,18 +178,14 @@ static int mincore_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
 		/* We need to do cache lookup too for pte markers */
 		if (pte_none_mostly(pte))
 			__mincore_unmapped_range(addr, addr + PAGE_SIZE,
 						 vma, vec);
 		else if (pte_present(pte)) {
-			unsigned int batch = pte_batch_hint(ptep, pte);
-
-			if (batch > 1) {
-				unsigned int max_nr = (end - addr) >> PAGE_SHIFT;
-
-				step = min_t(unsigned int, batch, max_nr);
-			}
+			unsigned int max_nr = (end - addr) >> PAGE_SHIFT;
 
+			step = can_pte_batch_count(vma, ptep, &pte,
+						   max_nr, 0);
 			for (i = 0; i < step; i++)
 				vec[i] = 1;
 		} else { /* pte is a swap entry */
 			*vec = mincore_swap(pte_to_swp_entry(pte), false);
 		}
-- 
2.43.0

Re: [RFC PATCH 2/3] mm/mincore: Use can_pte_batch_count() in mincore_pte_range() for pte batch mincore_pte_range()

[David Hildenbrand]

On 27.10.25 15:03, Zhang Qilong wrote:
> In current mincore_pte_range(), if pte_batch_hint() return one
> pte, it's not efficient, just call new added can_pte_batch_count().
> 
> In ARM64 qemu, with 8 CPUs, 32G memory, a simple test demo like:
> 1. mmap 1G anon memory
> 2. write 1G data by 4k step
> 3. mincore the mmaped 1G memory
> 4. get the time consumed by mincore
> 
> Tested the following cases:
>   - 4k, disabled all hugepage setting.
>   - 64k mTHP, only enable 64k hugepage setting.
> 
> Before
> 
> Case status | Consumed time (us)  |
> ----------------------------------|
> 4k          | 7356                |
> 64k mTHP    | 3670                |
> 
> Pathed:
> 
> Case status | Consumed time (us)  |
> ----------------------------------|
> 4k          | 4419                |
> 64k mTHP    | 3061                |
> 

I assume you're only lucky in that benchmark because you got consecutive 
4k pages / 64k mTHP from the buddy, right?

So I suspect that this will mostly just make a micro benchmark happy, 
because the reality where we allocate randomly over time, for the PCP, 
etc will look quite different.

-- 
Cheers

David / dhildenb

Re: [RFC PATCH 2/3] mm/mincore: Use can_pte_batch_count() in mincore_pte_range() for pte batch mincore_pte_range()

[Lorenzo Stoakes]

On Mon, Oct 27, 2025 at 10:03:14PM +0800, Zhang Qilong wrote:
> In current mincore_pte_range(), if pte_batch_hint() return one
> pte, it's not efficient, just call new added can_pte_batch_count().
>
> In ARM64 qemu, with 8 CPUs, 32G memory, a simple test demo like:
> 1. mmap 1G anon memory
> 2. write 1G data by 4k step
> 3. mincore the mmaped 1G memory
> 4. get the time consumed by mincore
>
> Tested the following cases:
>  - 4k, disabled all hugepage setting.
>  - 64k mTHP, only enable 64k hugepage setting.
>
> Before
>
> Case status | Consumed time (us)  |
> ----------------------------------|
> 4k          | 7356                |
> 64k mTHP    | 3670                |
>
> Pathed:
>
> Case status | Consumed time (us)  |
> ----------------------------------|
> 4k          | 4419                |
> 64k mTHP    | 3061                |
>
> The result is evident and demonstrate a significant improvement in
> the pte batch. While verification within a single environment may
> have inherent randomness. there is a high probability of achieving
> positive effects.

Recent batch PTE series seriously regressed non-arm, so I'm afraid we can't
accept any series that doesn't show statistics for _other platforms_.

Please make sure you at least test x86-64.

This code is very sensitive and we're not going to accept a patch like this
without _being sure_ it's ok.

>
> Signed-off-by: Zhang Qilong <zhangqilong3@huawei.com>
> ---
>  mm/mincore.c | 10 +++-------
>  1 file changed, 3 insertions(+), 7 deletions(-)
>
> diff --git a/mm/mincore.c b/mm/mincore.c
> index 8ec4719370e1..2cc5d276d1cd 100644
> --- a/mm/mincore.c
> +++ b/mm/mincore.c
> @@ -178,18 +178,14 @@ static int mincore_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
>  		/* We need to do cache lookup too for pte markers */
>  		if (pte_none_mostly(pte))
>  			__mincore_unmapped_range(addr, addr + PAGE_SIZE,
>  						 vma, vec);
>  		else if (pte_present(pte)) {
> -			unsigned int batch = pte_batch_hint(ptep, pte);
> -
> -			if (batch > 1) {
> -				unsigned int max_nr = (end - addr) >> PAGE_SHIFT;
> -
> -				step = min_t(unsigned int, batch, max_nr);
> -			}
> +			unsigned int max_nr = (end - addr) >> PAGE_SHIFT;
>
> +			step = can_pte_batch_count(vma, ptep, &pte,
> +						   max_nr, 0);
>  			for (i = 0; i < step; i++)
>  				vec[i] = 1;
>  		} else { /* pte is a swap entry */
>  			*vec = mincore_swap(pte_to_swp_entry(pte), false);
>  		}
> --
> 2.43.0
>