This is a note to let you know that I've just added the patch titled
mm, x86/mm: Fix performance regression in get_user_pages_fast()
to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
mm-x86-mm-fix-performance-regression-in-get_user_pages_fast.patch
and it can be found in the queue-4.14 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From foo@baz Wed Dec 6 18:04:41 CET 2017
From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Date: Sat, 9 Sep 2017 00:56:03 +0300
Subject: mm, x86/mm: Fix performance regression in get_user_pages_fast()
From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
[ Upstream commit 5b65c4677a57a1d4414212f9995aa0e46a21ff80 ]
The 0-day test bot found a performance regression that was tracked down to
switching x86 to the generic get_user_pages_fast() implementation:
http://lkml.kernel.org/r/20170710024020.GA26389@yexl-desktop
The regression was caused by the fact that we now use local_irq_save() +
local_irq_restore() in get_user_pages_fast() to disable interrupts.
In x86 implementation local_irq_disable() + local_irq_enable() was used.
The fix is to make get_user_pages_fast() use local_irq_disable(),
leaving local_irq_save() for __get_user_pages_fast() that can be called
with interrupts disabled.
Numbers for pinning a gigabyte of memory, one page a time, 20 repeats:
Before: Average: 14.91 ms, stddev: 0.45 ms
After: Average: 10.76 ms, stddev: 0.18 ms
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Huang Ying <ying.huang@xxxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Thorsten Leemhuis <regressions@xxxxxxxxxxxxx>
Cc: linux-mm@xxxxxxxxx
Fixes: e585513b76f7 ("x86/mm/gup: Switch GUP to the generic get_user_page_fast() implementation")
Link: http://lkml.kernel.org/r/20170908215603.9189-3-kirill.shutemov@xxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
mm/gup.c | 97 +++++++++++++++++++++++++++++++++++++--------------------------
1 file changed, 58 insertions(+), 39 deletions(-)
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1707,6 +1707,47 @@ static int gup_p4d_range(pgd_t pgd, unsi
return 1;
}
+static void gup_pgd_range(unsigned long addr, unsigned long end,
+ int write, struct page **pages, int *nr)
+{
+ unsigned long next;
+ pgd_t *pgdp;
+
+ pgdp = pgd_offset(current->mm, addr);
+ do {
+ pgd_t pgd = READ_ONCE(*pgdp);
+
+ next = pgd_addr_end(addr, end);
+ if (pgd_none(pgd))
+ return;
+ if (unlikely(pgd_huge(pgd))) {
+ if (!gup_huge_pgd(pgd, pgdp, addr, next, write,
+ pages, nr))
+ return;
+ } else if (unlikely(is_hugepd(__hugepd(pgd_val(pgd))))) {
+ if (!gup_huge_pd(__hugepd(pgd_val(pgd)), addr,
+ PGDIR_SHIFT, next, write, pages, nr))
+ return;
+ } else if (!gup_p4d_range(pgd, addr, next, write, pages, nr))
+ return;
+ } while (pgdp++, addr = next, addr != end);
+}
+
+#ifndef gup_fast_permitted
+/*
+ * Check if it's allowed to use __get_user_pages_fast() for the range, or
+ * we need to fall back to the slow version:
+ */
+bool gup_fast_permitted(unsigned long start, int nr_pages, int write)
+{
+ unsigned long len, end;
+
+ len = (unsigned long) nr_pages << PAGE_SHIFT;
+ end = start + len;
+ return end >= start;
+}
+#endif
+
/*
* Like get_user_pages_fast() except it's IRQ-safe in that it won't fall back to
* the regular GUP. It will only return non-negative values.
@@ -1714,10 +1755,8 @@ static int gup_p4d_range(pgd_t pgd, unsi
int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
struct page **pages)
{
- struct mm_struct *mm = current->mm;
unsigned long addr, len, end;
- unsigned long next, flags;
- pgd_t *pgdp;
+ unsigned long flags;
int nr = 0;
start &= PAGE_MASK;
@@ -1741,45 +1780,15 @@ int __get_user_pages_fast(unsigned long
* block IPIs that come from THPs splitting.
*/
- local_irq_save(flags);
- pgdp = pgd_offset(mm, addr);
- do {
- pgd_t pgd = READ_ONCE(*pgdp);
-
- next = pgd_addr_end(addr, end);
- if (pgd_none(pgd))
- break;
- if (unlikely(pgd_huge(pgd))) {
- if (!gup_huge_pgd(pgd, pgdp, addr, next, write,
- pages, &nr))
- break;
- } else if (unlikely(is_hugepd(__hugepd(pgd_val(pgd))))) {
- if (!gup_huge_pd(__hugepd(pgd_val(pgd)), addr,
- PGDIR_SHIFT, next, write, pages, &nr))
- break;
- } else if (!gup_p4d_range(pgd, addr, next, write, pages, &nr))
- break;
- } while (pgdp++, addr = next, addr != end);
- local_irq_restore(flags);
+ if (gup_fast_permitted(start, nr_pages, write)) {
+ local_irq_save(flags);
+ gup_pgd_range(addr, end, write, pages, &nr);
+ local_irq_restore(flags);
+ }
return nr;
}
-#ifndef gup_fast_permitted
-/*
- * Check if it's allowed to use __get_user_pages_fast() for the range, or
- * we need to fall back to the slow version:
- */
-bool gup_fast_permitted(unsigned long start, int nr_pages, int write)
-{
- unsigned long len, end;
-
- len = (unsigned long) nr_pages << PAGE_SHIFT;
- end = start + len;
- return end >= start;
-}
-#endif
-
/**
* get_user_pages_fast() - pin user pages in memory
* @start: starting user address
@@ -1799,12 +1808,22 @@ bool gup_fast_permitted(unsigned long st
int get_user_pages_fast(unsigned long start, int nr_pages, int write,
struct page **pages)
{
+ unsigned long addr, len, end;
int nr = 0, ret = 0;
start &= PAGE_MASK;
+ addr = start;
+ len = (unsigned long) nr_pages << PAGE_SHIFT;
+ end = start + len;
+
+ if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
+ (void __user *)start, len)))
+ return 0;
if (gup_fast_permitted(start, nr_pages, write)) {
- nr = __get_user_pages_fast(start, nr_pages, write, pages);
+ local_irq_disable();
+ gup_pgd_range(addr, end, write, pages, &nr);
+ local_irq_enable();
ret = nr;
}
Patches currently in stable-queue which might be from kirill.shutemov@xxxxxxxxxxxxxxx are
queue-4.14/mm-x86-mm-fix-performance-regression-in-get_user_pages_fast.patch