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Message-ID: <a98bc945-0020-40ce-a650-47dcd0274001@redhat.com>
Date: Fri, 30 May 2025 13:31:26 +0200
From: David Hildenbrand <david@...hat.com>
To: lizhe.67@...edance.com, akpm@...ux-foundation.org, jgg@...pe.ca,
jhubbard@...dia.com, peterx@...hat.com
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org, muchun.song@...ux.dev
Subject: Re: [PATCH] gup: optimize longterm pin_user_pages() for large folio
On 30.05.25 11:23, lizhe.67@...edance.com wrote:
> From: Li Zhe <lizhe.67@...edance.com>
>
> In the current implementation of the longterm pin_user_pages() function,
> we invoke the collect_longterm_unpinnable_folios() function. This function
> iterates through the list to check whether each folio belongs to the
> "longterm_unpinnabled" category. The folios in this list essentially
> correspond to a contiguous region of user-space addresses, with each folio
> representing a physical address in increments of PAGESIZE. If this
> user-space address range is mapped with large folio, we can optimize the
> performance of function pin_user_pages() by reducing the number of if-else
> branches and the frequency of memory accesses using READ_ONCE. This patch
> leverages this approach to achieve performance improvements.
>
> The performance test results obtained through the gup_test tool from the
> kernel source tree are as follows. We achieve an improvement of over 75%
> for large folio with pagesize=2M. For normal page, we have only observed
> a very slight degradation in performance.
>
> Without this patch:
>
> [root@...alhost ~] ./gup_test -HL -m 8192 -n 512
> TAP version 13
> 1..1
> # PIN_LONGTERM_BENCHMARK: Time: get:13623 put:10799 us#
> ok 1 ioctl status 0
> # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
> [root@...alhost ~]# ./gup_test -LT -m 8192 -n 512
> TAP version 13
> 1..1
> # PIN_LONGTERM_BENCHMARK: Time: get:129733 put:31753 us#
> ok 1 ioctl status 0
> # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
>
> With this patch:
>
> [root@...alhost ~] ./gup_test -HL -m 8192 -n 512
> TAP version 13
> 1..1
> # PIN_LONGTERM_BENCHMARK: Time: get:3386 put:10844 us#
> ok 1 ioctl status 0
> # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
> [root@...alhost ~]# ./gup_test -LT -m 8192 -n 512
> TAP version 13
> 1..1
> # PIN_LONGTERM_BENCHMARK: Time: get:131652 put:31393 us#
> ok 1 ioctl status 0
> # Totals: pass:1 fail:0 xfail:0 xpass:0 skip:0 error:0
>
> Signed-off-by: Li Zhe <lizhe.67@...edance.com>
> ---
> mm/gup.c | 31 +++++++++++++++++++++++--------
> 1 file changed, 23 insertions(+), 8 deletions(-)
>
> diff --git a/mm/gup.c b/mm/gup.c
> index 84461d384ae2..8c11418036e2 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -2317,6 +2317,25 @@ static void pofs_unpin(struct pages_or_folios *pofs)
> unpin_user_pages(pofs->pages, pofs->nr_entries);
> }
>
> +static struct folio *pofs_next_folio(struct folio *folio,
> + struct pages_or_folios *pofs, long *index_ptr)
> +{
> + long i = *index_ptr + 1;
> + unsigned long nr_pages = folio_nr_pages(folio);
> +
> + if (!pofs->has_folios)
> + while ((i < pofs->nr_entries) &&
> + /* Is this page part of this folio? */
> + (folio_page_idx(folio, pofs->pages[i]) < nr_pages))
passing in a page that does not belong to the folio looks shaky and not
future proof.
folio_page() == folio
is cleaner
--
Cheers,
David / dhildenb
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