Re: [PATCH -rt] Fix kmap_high_get()

Uwe Kleine-König
2009-08-14T20:13:11Z

Hello,

On Fri, Aug 14, 2009 at 11:58:59AM -0400, Nicolas Pitre wrote:
> On Fri, 14 Aug 2009, Peter Zijlstra wrote:
>
> > As to the patch, its not quite right.
... on irc Peter and me agreed it's not that wrong :-) Anyhow, I merged
the two patches to get the benefits from both. See below.

> > From what I understand kmap_high_get() is used to pin a page's kmap iff
> > it has one, whereas the result of your patch seems to be that it'll
> > actually create one if its not found.
>
> I don't have enough context to review this patch, but your understanding
> of the kmap_high_get() purpose is right.
The patch with all it's dependencies based on -rc6 is available on

git://git.pengutronix.de/git/ukl/linux-2.6.git kmap-testing

Niko: Your review would be very welcome because neither Peter nor me
have a machine with highmem.

Best regards
Uwe

>From fafb2e9964cd01535a61f20a45093ba053169f06 Mon Sep 17 00:00:00 2001
From: =?utf-8?q?Uwe=20Kleine-K=C3=B6nig?= <u.kleine-koenig@pengutronix.de>
Date: Fri, 14 Aug 2009 21:45:55 +0200
Subject: [PATCH] Fix kmap_high_get() as kmap locking is gone
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
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This has the pros of both Peter's and my patch:

- It obsoletes ARCH_NEEDS_KMAP_HIGH_GET without introducing a big
overhead for the archs not having defined that symbol.
- no code duplication between kmap_high_get and kmap_high
- a nice kmap_high_put function that does the same as kunmap_high
without accounting
- no compiler warning about mismatched declarations

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Cc: Nicolas Pitre <nico@marvell.com>
Cc: MinChan Kim <minchan.kim@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Li Zefan <lizf@cn.fujitsu.com>
Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
---
arch/arm/include/asm/highmem.h | 3 +-
arch/arm/mm/dma-mapping.c | 2 +-
mm/highmem.c | 98 +++++++++++++++++-----------------------
3 files changed, 43 insertions(+), 60 deletions(-)

diff --git a/arch/arm/include/asm/highmem.h b/arch/arm/include/asm/highmem.h
index 7f36d00..2082ed8 100644
--- a/arch/arm/include/asm/highmem.h
+++ b/arch/arm/include/asm/highmem.h
@@ -15,10 +15,9 @@

extern pte_t *pkmap_page_table;

-#define ARCH_NEEDS_KMAP_HIGH_GET
-
extern void *kmap_high(struct page *page);
extern void *kmap_high_get(struct page *page);
+extern void kmap_high_put(struct page *page);
extern void kunmap_high(struct page *page);

extern void *kmap(struct page *page);
diff --git a/arch/arm/mm/dma-mapping.c b/arch/arm/mm/dma-mapping.c
index 510c179..d71aff9 100644
--- a/arch/arm/mm/dma-mapping.c
+++ b/arch/arm/mm/dma-mapping.c
@@ -551,7 +551,7 @@ static void dma_cache_maint_contiguous(struct page *page, unsigned long offset,
if (vaddr) {
vaddr += offset;
inner_op(vaddr, vaddr + size);
- kunmap_high(page);
+ kmap_high_put(page);
}
}

diff --git a/mm/highmem.c b/mm/highmem.c
index 4aa9eea..1043938 100644
--- a/mm/highmem.c
+++ b/mm/highmem.c
@@ -75,26 +75,6 @@ pte_t * pkmap_page_table;

static DECLARE_WAIT_QUEUE_HEAD(pkmap_wait);

-
-/*
- * Most architectures have no use for kmap_high_get(), so let's abstract
- * the disabling of IRQ out of the locking in that case to save on a
- * potential useless overhead.
- */
-#ifdef ARCH_NEEDS_KMAP_HIGH_GET
-#define lock_kmap() spin_lock_irq(&kmap_lock)
-#define unlock_kmap() spin_unlock_irq(&kmap_lock)
-#define lock_kmap_any(flags) spin_lock_irqsave(&kmap_lock, flags)
-#define unlock_kmap_any(flags) spin_unlock_irqrestore(&kmap_lock, flags)
-#else
-#define lock_kmap() spin_lock(&kmap_lock)
-#define unlock_kmap() spin_unlock(&kmap_lock)
-#define lock_kmap_any(flags) \
- do { spin_lock(&kmap_lock); (void)(flags); } while (0)
-#define unlock_kmap_any(flags) \
- do { spin_unlock(&kmap_lock); (void)(flags); } while (0)
-#endif
-
/*
* Try to free a given kmap slot.
*
@@ -313,22 +293,32 @@ static void kunmap_account(void)
wake_up(&pkmap_wait);
}

-void *kmap_high(struct page *page)
+/**
+ * kmap_high_get - pin a highmem page into memory
+ * @page: &struct page to pin
+ *
+ * Returns the page's current virtual memory address, or NULL if no mapping
+ * exists. When and only when a non null address is returned then a
+ * matching call to kmap_high_put() is necessary.
+ *
+ * This can be called from any context.
+ */
+void *kmap_high_get(struct page *page)
{
unsigned long vaddr;

-
- kmap_account();
again:
vaddr = (unsigned long)page_address(page);
if (vaddr) {
atomic_t *counter = &pkmap_count[PKMAP_NR(vaddr)];
if (atomic_inc_not_zero(counter)) {
/*
- * atomic_inc_not_zero implies a (memory) barrier on success
- * so page address will be reloaded.
+ * atomic_inc_not_zero implies a (memory) barrier on
+ * success, so page address will be reloaded.
*/
- unsigned long vaddr2 = (unsigned long)page_address(page);
+ unsigned long vaddr2 =
+ (unsigned long)page_address(page);
+
if (likely(vaddr == vaddr2))
return (void *)vaddr;

@@ -345,46 +335,40 @@ again:
}
}

+ return NULL;
+}
+EXPORT_SYMBOL(kmap_high_get);
+
+void kmap_high_put(struct page *page)
+{
+ unsigned long vaddr = (unsigned long)page_address(page);
+
+ BUG_ON(!vaddr);
+ pkmap_put(&pkmap_count[PKMAP_NR(vaddr)]);
+}
+EXPORT_SYMBOL(kmap_high_put);
+
+void *kmap_high(struct page *page)
+{
+ unsigned long vaddr;
+
+ kmap_account();
+again:
+ vaddr = (unsigned long)kmap_high_get(page);
+ if (vaddr)
+ return (void *)vaddr;
+
vaddr = pkmap_insert(page);
if (!vaddr)
goto again;

return (void *)vaddr;
}
-
EXPORT_SYMBOL(kmap_high);

-#ifdef ARCH_NEEDS_KMAP_HIGH_GET
-/**
- * kmap_high_get - pin a highmem page into memory
- * @page: &struct page to pin
- *
- * Returns the page's current virtual memory address, or NULL if no mapping
- * exists. When and only when a non null address is returned then a
- * matching call to kunmap_high() is necessary.
- *
- * This can be called from any context.
- */
-void *kmap_high_get(struct page *page)
-{
- unsigned long vaddr, flags;
-
- lock_kmap_any(flags);
- vaddr = (unsigned long)page_address(page);
- if (vaddr) {
- BUG_ON(atomic_read(&pkmap_count[PKMAP_NR(vaddr)]) < 1);
- atomic_add(1, pkmap_count[PKMAP_NR(vaddr)]);
- }
- unlock_kmap_any(flags);
- return (void*) vaddr;
-}
-#endif
-
- void kunmap_high(struct page *page)
+void kunmap_high(struct page *page)
{
- unsigned long vaddr = (unsigned long)page_address(page);
- BUG_ON(!vaddr);
- pkmap_put(&pkmap_count[PKMAP_NR(vaddr)]);
+ kmap_high_put(page);
kunmap_account();
}

--
1.6.3.3

--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | http://www.pengutronix.de/ |

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