linux-kernel - Re: [linus:master] [mm] f822a9a81a: stress-ng.bigheap.realloc_calls_per

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Message-ID: <d8e0f3b3-6ea7-492b-bb94-4f5d1ab28ef2@redhat.com>
Date: Thu, 7 Aug 2025 20:31:18 +0200
From: David Hildenbrand <david@...hat.com>
To: Jann Horn <jannh@...gle.com>
Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 kernel test robot <oliver.sang@...el.com>, Dev Jain <dev.jain@....com>,
 oe-lkp@...ts.linux.dev, lkp@...el.com, linux-kernel@...r.kernel.org,
 Andrew Morton <akpm@...ux-foundation.org>, Barry Song <baohua@...nel.org>,
 Pedro Falcato <pfalcato@...e.de>,
 Anshuman Khandual <anshuman.khandual@....com>,
 Bang Li <libang.li@...group.com>, Baolin Wang
 <baolin.wang@...ux.alibaba.com>, bibo mao <maobibo@...ngson.cn>,
 Hugh Dickins <hughd@...gle.com>, Ingo Molnar <mingo@...nel.org>,
 Lance Yang <ioworker0@...il.com>, Liam Howlett <liam.howlett@...cle.com>,
 Matthew Wilcox <willy@...radead.org>, Peter Xu <peterx@...hat.com>,
 Qi Zheng <zhengqi.arch@...edance.com>, Ryan Roberts <ryan.roberts@....com>,
 Vlastimil Babka <vbabka@...e.cz>, Yang Shi <yang@...amperecomputing.com>,
 Zi Yan <ziy@...dia.com>, linux-mm@...ck.org
Subject: Re: [linus:master] [mm] f822a9a81a:
 stress-ng.bigheap.realloc_calls_per_sec 37.3% regression

On 07.08.25 20:07, Jann Horn wrote:
> On Thu, Aug 7, 2025 at 8:02 PM David Hildenbrand <david@...hat.com> wrote:
>> Sure, we could use pte_batch_hint(), but I'm curious if x86 would also
>> benefit with larger folios (e.g., 64K, 128K) with this patch.
> 
> Where would you expect such a benefit to come from? This function is
> more or less a memcpy(), except it has to read PTEs with xchg(), write
> them atomically, and set softdirty flags. For x86, what the associated
> folios look like and whether the PTEs are contiguous shouldn't matter.
> 

Good point, I was assuming TLB flushing as well, but that doesn't really 
apply here because we are already batching that.

-- 
Cheers,

David / dhildenb