Messages in this thread |  | | Date | Wed, 8 Apr 2026 19:09:34 -0700 | | Subject | Re: [PATCH] mm/gup: fix GUP-fast fallback for NULL-mapping order-0 folios | | From | John Hubbard <> |
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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
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