Re: [PATCH] mm/page_alloc: remove prefetchw() on freeing page to buddy system

[Wei Yang <richard.weiyang@gmail.com>]

On Mon, Jul 01, 2024 at 11:22:24PM -0700, Andrew Morton wrote:
>On Tue,  2 Jul 2024 02:09:31 +0000 Wei Yang <richard.weiyang@gmail.com> wrote:
>
>> The prefetchw() is introduced from an ancient patch[1].
>> 
>> The change log says:
>> 
>>     The basic idea is to free higher order pages instead of going
>>     through every single one.  Also, some unnecessary atomic operations
>>     are done away with and replaced with non-atomic equivalents, and
>>     prefetching is done where it helps the most.  For a more in-depth
>>     discusion of this patch, please see the linux-ia64 archives (topic
>>     is "free bootmem feedback patch").
>> 
>> So there are several changes improve the bootmem freeing, in which the
>> most basic idea is freeing higher order pages. And as Matthew says,
>> "Itanium CPUs of this era had no prefetchers."
>> 
>> I did 10 round bootup tests before and after this change, the data
>> doesn't prove prefetchw() help speeding up bootmem freeing. The sum of
>> the 10 round bootmem freeing time after prefetchw() removal even 5.2%
>> faster than before.
>
>I don't think I've ever seen prefetch make a damn bit of difference.
>
>> [1]: https://lore.kernel.org/linux-ia64/40F46962.4090604@sgi.com/
>> 
>> Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
>> Suggested-by: Matthew Wilcox <willy@infradead.org>
>> CC: David Hildenbrand <david@redhat.com>
>> 
>> ---
>> The patch is based on mm-stable with David's change.
>
>Oh help.  David makes many changes.  Please identify patches with much
>care.  Fully quoting the email title works, as does a link.
>

The commit is 3dadec1babf9eee0c67c967df931d6f0cb124a04

  mm: pass meminit_context to __free_pages_core()

The link is, if I am correct.
https://lore.kernel.org/all/20240607090939.89524-2-david@redhat.com/

BTW, how we track the mail link? Just search in lore.kernel.org?

-- 
Wei Yang
Help you, Help me