From: John Hubbard <jhubbard@nvidia.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: David Hildenbrand <david@kernel.org>,
Jason Gunthorpe <jgg@ziepe.ca>, Peter Xu <peterx@redhat.com>,
Mike Rapoport <rppt@kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
linux-mm@kvack.org, Sourab Gupta <sougupta@nvidia.com>
Subject: Re: [PATCH] mm/gup: fix GUP-fast fallback for NULL-mapping order-0 folios
Date: Wed, 8 Apr 2026 19:09:34 -0700 [thread overview]
Message-ID: <d957b695-3caa-44ce-9853-f0f221fa0e88@nvidia.com> (raw)
In-Reply-To: <20260408190745.40f0c0231a475e697c970fd4@linux-foundation.org>
On 4/8/26 7:07 PM, Andrew Morton wrote:
> On Wed, 8 Apr 2026 18:46:47 -0700 John Hubbard <jhubbard@nvidia.com> wrote:
>
>> Since commit f002882ca369 ("mm: merge folio_is_secretmem() and
>> folio_fast_pin_allowed() into gup_fast_folio_allowed()"),
>> gup_fast_folio_allowed() falls back to the slow path for any order-0
>> folio with a NULL mapping when CONFIG_SECRETMEM=y. This causes a
>> performance regression for drivers that allocate pages with alloc_page()
>> and insert them into VMAs via vm_insert_page(). These pages legitimately
>> have a NULL folio->mapping, but they cannot be secretmem pages.
>
> How significant is the slowdown?
About 2x!
Sourab has a bunch of peer to peer IO cases that use 4K pages,
that he ran.
thanks,
--
John Hubbard
prev parent reply other threads:[~2026-04-09 2:09 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-09 1:46 John Hubbard
2026-04-09 2:07 ` Andrew Morton
2026-04-09 2:09 ` John Hubbard [this message]
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