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Message-ID: <20250530092351.32709-1-lizhe.67@bytedance.com>
Date: Fri, 30 May 2025 17:23:51 +0800
From: lizhe.67@...edance.com
To: akpm@...ux-foundation.org,
david@...hat.com,
jgg@...pe.ca,
jhubbard@...dia.com,
peterx@...hat.com
Cc: linux-mm@...ck.org,
linux-kernel@...r.kernel.org,
muchun.song@...ux.dev,
lizhe.67@...edance.com
Subject: [PATCH] gup: optimize longterm pin_user_pages() for large folio
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))
+ i++;
+
+ if (unlikely(i == pofs->nr_entries))
+ return NULL;
+ *index_ptr = i;
+
+ return pofs_get_folio(pofs, i);
+}
+
/*
* Returns the number of collected folios. Return value is always >= 0.
*/
@@ -2324,16 +2343,12 @@ 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;
- if (folio == prev_folio)
- continue;
- prev_folio = folio;
+ for (folio = pofs_get_folio(pofs, 0); folio;
+ folio = pofs_next_folio(folio, pofs, &i)) {
if (folio_is_longterm_pinnable(folio))
continue;
--
2.20.1
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