| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <20250604091131.32908-1-lizhe.67@bytedance.com>
Date: Wed, 4 Jun 2025 17:11:31 +0800
From: lizhe.67@...edance.com
To: david@...hat.com
Cc: akpm@...ux-foundation.org,
dev.jain@....com,
jgg@...pe.ca,
jhubbard@...dia.com,
linux-kernel@...r.kernel.org,
linux-mm@...ck.org,
lizhe.67@...edance.com,
muchun.song@...ux.dev,
peterx@...hat.com
Subject: Re: [PATCH v2] gup: optimize longterm pin_user_pages() for large folio
On Wed, 4 Jun 2025 10:12:00 +0200, david@...hat.com wrote:
> On 04.06.25 05:15, 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 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 70%
> > 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:4075 put:10792 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:130727 put:31763 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>
> > ---
> > Changelogs:
> >
> > v1->v2:
> > - Modify some unreliable code.
> > - Update performance test data.
> >
> > v1 patch: https://lore.kernel.org/all/20250530092351.32709-1-lizhe.67@bytedance.com/
> >
> > mm/gup.c | 37 +++++++++++++++++++++++++++++--------
> > 1 file changed, 29 insertions(+), 8 deletions(-)
> >
> > diff --git a/mm/gup.c b/mm/gup.c
> > index 84461d384ae2..57fd324473a1 100644
> > --- a/mm/gup.c
> > +++ b/mm/gup.c
> > @@ -2317,6 +2317,31 @@ 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;
> > +
> > + if (!pofs->has_folios) {
>
> && folio_test_large(folio)
>
> To avoid all that for small folios.
Great! This approach will minimize the impact on small folios.
> > + unsigned long start_pfn = folio_pfn(folio);> + unsigned long end_pfn = start_pfn + folio_nr_pages(folio);
>
> I guess both could be const
>
> > +> + for (; i < pofs->nr_entries; i++) {
> > + unsigned long pfn = page_to_pfn(pofs->pages[i]);
> > +
> > + /* Is this page part of this folio? */
> > + if ((pfn < start_pfn) || (pfn >= end_pfn))
>
> No need for the inner ()
>
> > + break;
> > + }
> > + }
> > +
> > + if (unlikely(i == pofs->nr_entries))
> > + return NULL;
> > + *index_ptr = i;> +
> > + return pofs_get_folio(pofs, i);
>
> We're now doing two "pofs->has_folios" checks. Maybe the compiler is
> smart enough to figure that out.
I also hope that the compiler can optimize this logic.
> > +}
> > +
> > /*> * Returns the number of collected folios. Return value is always >= 0.
> > */
> > @@ -2324,16 +2349,12 @@ static void collect_longterm_unpinnable_folios(
> > struct list_head *movable_folio_list,
> > struct pages_or_folios *pofs)
> > {
> > - struct folio *prev_folio = NULL;
> > bool drain_allow = true;
> > - unsigned long i;
> > -
> > - for (i = 0; i < pofs->nr_entries; i++) {
> > - struct folio *folio = pofs_get_folio(pofs, i);
> > + long i = 0;
> > + struct folio *folio;
>
> Please keep the reverse christmas tree where we have it. Why
> the change from "unsigned long" -> "long" ?
This is because I want to match the type of pages_or_folios->nr_entries.
I'm not sure if it's necessary.
> >
> > - if (folio == prev_folio)
> > - continue;
> > - prev_folio = folio;
> > + for (folio = pofs_get_folio(pofs, 0); folio;
> > + folio = pofs_next_folio(folio, pofs, &i)) {
>
> Please indent as
>
> for (folio = pofs_get_folio(pofs, 0); folio;
> folio = pofs_next_folio(folio, pofs, &i)) {
>
> But the usage of "0" and "&i" is a bit suboptimal.
>
> for (folio = pofs_get_folio(pofs, i); folio;
> folio = pofs_next_folio(folio, pofs, &i)) {
>
> Might be better.
Thank you for all your suggestions! I will complete the amendments
as you advised.
Thanks,
Zhe
Powered by blists - more mailing lists