Re: [PATCH 0/3] Optimize mremap() by PTE-batching

[Dev Jain <dev.jain@arm.com>]

On 06/05/25 4:14 pm, Lorenzo Stoakes wrote:
> On Tue, May 06, 2025 at 03:52:39PM +0530, Dev Jain wrote:
>>
>>
>> On 06/05/25 2:46 pm, Anshuman Khandual wrote:
>>> On 5/6/25 10:30, Dev Jain wrote:
>>>> Use PTE batching to optimize mremap().
>>>>
>>>> Mapping 512K of memory, memsetting it, remapping it to src + 512K, and
>>>> munmapping it 10,000 times, the average execution time reduces from 1.9 to
>>>> 1.2 seconds, giving a 37% performance optimization. (Apple M3)
>>>
>>> That's impressive improvement. But could you please re-organize the test
>>> description into a pseudo code format or better provide the test program
>>> itself (which should be compact anyways) just to be more clear about the
>>> scenario where this helps.
>>
>> Sure.
> 
> I echo Ashuman's comment, definitely would like to see that.
> 
> And wrt to perf improvement, whether it's a microbenchmark or not, that's a
> great result so well done :) I echo this also!
> 
> However, it'd be good to see some more detail here also, you're kind of missing
> out - everything - about why this improvement happens - what the intent of the
> series is, anything about large folios, under what circumstances you'll see an
> improvement, etc. etc.
> 
> While this might duplicate comments you've made elsewhere, it's mandatory for a
> series, and Andrew is unlikely to take this without it.
> 
> In mm we place the contents of the cover letter in the first commit in the
> series, so it gets stored for posterity also!
> 
> Cheers, Lorenzo

Thanks for your feedback. I'll make the required changes.

> 
>>
>>>
>>>>
>>>> Dev Jain (3):
>>>>     mm: Call pointers to ptes as ptep
>>>>     mm: Add generic helper to hint a large folio
>>>>     mm: Optimize mremap() by PTE batching
>>>>
>>>>    include/linux/pgtable.h | 16 +++++++++++++++
>>>>    mm/mremap.c             | 44 +++++++++++++++++++++++++++--------------
>>>>    2 files changed, 45 insertions(+), 15 deletions(-)
>>>>
>>