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

[zhangqilong <zhangqilong3@huawei.com>]

 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
> >