From: Pedro Falcato <pfalcato@suse.de>
To: "David Hildenbrand (Arm)" <david@kernel.org>
Cc: Luke Yang <luyang@redhat.com>,
dev.jain@arm.com, jhladky@redhat.com, akpm@linux-foundation.org,
Liam.Howlett@oracle.com, willy@infradead.org, surenb@google.com,
vbabka@suse.cz, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [REGRESSION] mm/mprotect: 2x+ slowdown for >=400KiB regions since PTE batching (cac1db8c3aad)
Date: Fri, 13 Feb 2026 16:24:32 +0000 [thread overview]
Message-ID: <dhoz2eeqdx44sf2epeorxs67v5zohutgxniourumsouz22qbl7@gijuj43edjb4> (raw)
In-Reply-To: <c450ee86-4c34-449d-b144-6b4dcb996998@kernel.org>
On Fri, Feb 13, 2026 at 04:47:29PM +0100, David Hildenbrand (Arm) wrote:
> On 2/13/26 16:08, Luke Yang wrote:
> > Hello,
>
> Hi!
>
> >
> > we have bisected a significant mprotect() performance regression in
> > 6.17-rc1 to:
> >
> > cac1db8c3aad ("mm: optimize mprotect() by PTE batching")
> >
> > The regression becomes clearly visible starting around 400 KiB region
> > sizes and above. It is also still present in the latest 6.19 kernel.
> >
>
> Micro-benchmark results are nice. But what is the real word impact? IOW, why
> should we care?
Well, mprotect is widely used in thread spawning, code JITting,
and even process startup. And we don't want to pay for a feature we can't
even use (on x86).
In any case, I think I see the problem. Namely, that we now need to call
vm_normal_folio() for every single PTE (this seems similar to the mremap
problem caught in 0b5be138ce00f421bd7cc5a226061bd62c4ab850). I'll try to
draft up a patch over the weekend if I can.
--
Pedro
next prev parent reply other threads:[~2026-02-13 16:24 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-02-13 15:08 Luke Yang
2026-02-13 15:47 ` David Hildenbrand (Arm)
2026-02-13 16:24 ` Pedro Falcato [this message]
2026-02-13 17:16 ` Suren Baghdasaryan
2026-02-13 17:26 ` David Hildenbrand (Arm)
2026-02-16 10:12 ` Dev Jain
2026-02-16 14:56 ` Pedro Falcato
2026-02-17 17:43 ` Luke Yang
2026-02-17 18:08 ` Pedro Falcato
2026-02-18 5:01 ` Dev Jain
2026-02-18 10:06 ` Pedro Falcato
2026-02-18 10:38 ` Dev Jain
2026-02-18 10:46 ` David Hildenbrand (Arm)
2026-02-18 11:58 ` Pedro Falcato
2026-02-18 12:24 ` David Hildenbrand (Arm)
2026-02-19 12:15 ` Pedro Falcato
2026-02-19 13:02 ` David Hildenbrand (Arm)
2026-02-19 15:00 ` Pedro Falcato
2026-02-19 15:29 ` David Hildenbrand (Arm)
2026-02-20 4:12 ` Dev Jain
2026-02-18 11:52 ` Pedro Falcato
2026-02-18 4:50 ` Dev Jain
2026-02-18 13:29 ` David Hildenbrand (Arm)
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