From: Linus Torvalds <torvalds@linux-foundation.org>
To: Nicholas Piggin <npiggin@gmail.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>,
Bob Peterson <rpeterso@redhat.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Steven Whitehouse <swhiteho@redhat.com>,
Andrew Lutomirski <luto@kernel.org>,
Andreas Gruenbacher <agruenba@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
linux-mm <linux-mm@kvack.org>,
Mel Gorman <mgorman@techsingularity.net>
Subject: Re: [PATCH 2/2] mm: add PageWaiters indicating tasks are waiting for a page bit
Date: Tue, 27 Dec 2016 11:24:16 -0800 [thread overview]
Message-ID: <CA+55aFzNU53+9PT_xzrPRYdbUYP6V4Y52wCo8V_tANB0tLStnw@mail.gmail.com> (raw)
In-Reply-To: <CA+55aFzKuiLS0CvTTqo5=8eyoksC1==30+XMiXZhQqzXr9JM3A@mail.gmail.com>
[-- Attachment #1: Type: text/plain, Size: 342 bytes --]
On Tue, Dec 27, 2016 at 11:23 AM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> Of course, none of this is *tested*, but it looks superficially
> correct, and allows other architectures to do the same optimization if
> they want.
Oops. I should include the actual patch I was talking about too, shouldn't I?
Linus
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[-- Type: text/plain, Size: 2820 bytes --]
arch/x86/include/asm/bitops.h | 13 +++++++++++++
include/linux/page-flags.h | 2 +-
mm/filemap.c | 24 +++++++++++++++++++++---
3 files changed, 35 insertions(+), 4 deletions(-)
diff --git a/arch/x86/include/asm/bitops.h b/arch/x86/include/asm/bitops.h
index 68557f52b961..34eae484a173 100644
--- a/arch/x86/include/asm/bitops.h
+++ b/arch/x86/include/asm/bitops.h
@@ -139,6 +139,19 @@ static __always_inline void __clear_bit(long nr, volatile unsigned long *addr)
asm volatile("btr %1,%0" : ADDR : "Ir" (nr));
}
+static __always_inline bool clear_bit_unlock_is_negative_byte(long nr, volatile unsigned long *addr)
+{
+ bool negative;
+ asm volatile(LOCK_PREFIX "andb %2,%1\n\t"
+ CC_SET(s)
+ : CC_OUT(s) (negative), ADDR
+ : "Ir" (1 << nr) : "memory");
+ return negative;
+}
+
+// Let everybody know we have it
+#define clear_bit_unlock_is_negative_byte clear_bit_unlock_is_negative_byte
+
/*
* __clear_bit_unlock - Clears a bit in memory
* @nr: Bit to clear
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index c56b39890a41..6b5818d6de32 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -73,13 +73,13 @@
*/
enum pageflags {
PG_locked, /* Page is locked. Don't touch. */
- PG_waiters, /* Page has waiters, check its waitqueue */
PG_error,
PG_referenced,
PG_uptodate,
PG_dirty,
PG_lru,
PG_active,
+ PG_waiters, /* Page has waiters, check its waitqueue. Must be bit #7 and in the same byte as "PG_locked" */
PG_slab,
PG_owner_priv_1, /* Owner use. If pagecache, fs may use*/
PG_arch_1,
diff --git a/mm/filemap.c b/mm/filemap.c
index 82f26cde830c..01a2d4a6571c 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -912,6 +912,25 @@ void add_page_wait_queue(struct page *page, wait_queue_t *waiter)
}
EXPORT_SYMBOL_GPL(add_page_wait_queue);
+#ifndef clear_bit_unlock_is_negative_byte
+
+/*
+ * PG_waiters is the high bit in the same byte as PG_lock.
+ *
+ * On x86 (and on many other architectures), we can clear PG_lock and
+ * test the sign bit at the same time. But if the architecture does
+ * not support that special operation, we just do this all by hand
+ * instead.
+ */
+static inline bool clear_bit_unlock_is_negative_byte(long nr, volatile void *mem)
+{
+ clear_bit_unlock(PG_locked, mem);
+ smp_mb__after_atomic();
+ return test_bit(PG_waiters);
+}
+
+#endif
+
/**
* unlock_page - unlock a locked page
* @page: the page
@@ -928,9 +947,8 @@ void unlock_page(struct page *page)
{
page = compound_head(page);
VM_BUG_ON_PAGE(!PageLocked(page), page);
- clear_bit_unlock(PG_locked, &page->flags);
- smp_mb__after_atomic();
- wake_up_page(page, PG_locked);
+ if (clear_bit_unlock_is_negative_byte(PG_locked, &page->flags))
+ wake_up_page_bit(page, PG_locked);
}
EXPORT_SYMBOL(unlock_page);
next prev parent reply other threads:[~2016-12-27 19:33 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-25 3:00 [PATCH 0/2] PageWaiters again Nicholas Piggin
2016-12-25 3:00 ` [PATCH 1/2] mm: Use owner_priv bit for PageSwapCache, valid when PageSwapBacked Nicholas Piggin
2016-12-25 5:13 ` Hugh Dickins
2016-12-25 3:00 ` [PATCH 2/2] mm: add PageWaiters indicating tasks are waiting for a page bit Nicholas Piggin
2016-12-25 21:51 ` Linus Torvalds
2016-12-26 1:16 ` Nicholas Piggin
2016-12-26 19:07 ` Linus Torvalds
2016-12-27 11:19 ` Nicholas Piggin
2016-12-27 18:58 ` Linus Torvalds
2016-12-27 19:23 ` Linus Torvalds
2016-12-27 19:24 ` Linus Torvalds [this message]
2016-12-27 19:40 ` Linus Torvalds
2016-12-27 20:17 ` Linus Torvalds
2016-12-28 3:53 ` Nicholas Piggin
2016-12-28 19:17 ` Linus Torvalds
2016-12-29 4:08 ` Nicholas Piggin
2016-12-29 4:16 ` Linus Torvalds
2016-12-29 5:26 ` Nicholas Piggin
2017-01-03 10:24 ` Mel Gorman
2017-01-03 12:29 ` Nicholas Piggin
2017-01-03 17:18 ` Mel Gorman
2016-12-29 22:16 ` [PATCH] mm/filemap: fix parameters to test_bit() Olof Johansson
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