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Date: Wed, 15 Apr 2009 18:22:41 +0900
From: FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To: mingo@...e.hu
Cc: fujita.tomonori@....ntt.co.jp, linux-kernel@...r.kernel.org,
joerg.roedel@....com, akpm@...ux-foundation.org
Subject: Re: [PATCH 1/2] dma-debug: add dma_debug_resize_entries() to
adjust the number of dma_debug_entries
On Tue, 14 Apr 2009 12:58:23 +0200
Ingo Molnar <mingo@...e.hu> wrote:
>
> * FUJITA Tomonori <fujita.tomonori@....ntt.co.jp> wrote:
>
> > +int dma_debug_resize_entries(u32 num_entries)
> > +{
> > + int i, delta, ret = 0;
> > + unsigned long flags;
> > + struct dma_debug_entry *entry;
> > +
> > + spin_lock_irqsave(&free_entries_lock, flags);
> > +
> > + if (nr_total_entries < num_entries) {
> > + delta = num_entries - nr_total_entries;
> > +
> > + for (i = 0; i < delta; i++) {
> > + entry = kzalloc(sizeof(*entry), GFP_ATOMIC);
> > + if (!entry)
> > + break;
>
> hm, using GFP_ATOMIC within a spinlock is not a very nice thing to
> do in general. While this is boot-only and the GFP_ATOMIC will
> likely succeed, this could become non-boot functionality and then
> it's exposed to the momentary VM pressure situation that might make
> GFP_ATOMIC fail.
>
> Please fix this to be GFP_KERNEL.
Ok, fixed though I'm not sure it matters. It's unlikely that this could
become non-boot functionality so I chose a simple way.
I've attached a fixed patch. It's unlikely that this function is
called concurrently so I don't try hard.
> a small detail:
>
> > + delta = nr_total_entries - num_entries;
> > +
> > + for (i = 0; i < delta && !list_empty(&free_entries); i++) {
> > + entry = __dma_entry_alloc();
> > + kfree(entry);
> > + }
> > +
> > + nr_total_entries -= i;
> > + }
>
> Can i != delta ever happen? It would suggest the list length being
> out of sync with the nr_total_entries counter.
Yes, it can happen because only free entries are linked to
free_entries list. If some entries are already used, then it's
possible that we can't find enough entries in free_entries list here.
=
From: FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
Subject: [PATCH] dma-debug: add dma_debug_resize_entries() to adjust the number of dma_debug_entries
We use a static value for the number of dma_debug_entries. It can be
overwritten by a kernel command line option.
Some IOMMUs (e.g. GART) can't set an appropriate value by a kernel
command line option because they can't know such value until they
finish initializing up their hardware.
This patch adds dma_debug_resize_entries() enables IOMMUs to adjust
the number of dma_debug_entries anytime.
Signed-off-by: FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
---
include/linux/dma-debug.h | 7 ++++
lib/dma-debug.c | 72 +++++++++++++++++++++++++++++++++++++++++----
2 files changed, 73 insertions(+), 6 deletions(-)
diff --git a/include/linux/dma-debug.h b/include/linux/dma-debug.h
index 28d53cb..171ad8a 100644
--- a/include/linux/dma-debug.h
+++ b/include/linux/dma-debug.h
@@ -32,6 +32,8 @@ extern void dma_debug_add_bus(struct bus_type *bus);
extern void dma_debug_init(u32 num_entries);
+extern int dma_debug_resize_entries(u32 num_entries);
+
extern void debug_dma_map_page(struct device *dev, struct page *page,
size_t offset, size_t size,
int direction, dma_addr_t dma_addr,
@@ -91,6 +93,11 @@ static inline void dma_debug_init(u32 num_entries)
{
}
+static inline int dma_debug_resize_entries(u32 num_entries)
+{
+ return 0;
+}
+
static inline void debug_dma_map_page(struct device *dev, struct page *page,
size_t offset, size_t size,
int direction, dma_addr_t dma_addr,
diff --git a/lib/dma-debug.c b/lib/dma-debug.c
index d3da7ed..5d61019 100644
--- a/lib/dma-debug.c
+++ b/lib/dma-debug.c
@@ -85,6 +85,7 @@ static u32 show_num_errors = 1;
static u32 num_free_entries;
static u32 min_free_entries;
+static u32 nr_total_entries;
/* number of preallocated entries requested by kernel cmdline */
static u32 req_entries;
@@ -257,6 +258,21 @@ static void add_dma_entry(struct dma_debug_entry *entry)
put_hash_bucket(bucket, &flags);
}
+static struct dma_debug_entry *__dma_entry_alloc(void)
+{
+ struct dma_debug_entry *entry;
+
+ entry = list_entry(free_entries.next, struct dma_debug_entry, list);
+ list_del(&entry->list);
+ memset(entry, 0, sizeof(*entry));
+
+ num_free_entries -= 1;
+ if (num_free_entries < min_free_entries)
+ min_free_entries = num_free_entries;
+
+ return entry;
+}
+
/* struct dma_entry allocator
*
* The next two functions implement the allocator for
@@ -276,9 +292,7 @@ static struct dma_debug_entry *dma_entry_alloc(void)
goto out;
}
- entry = list_entry(free_entries.next, struct dma_debug_entry, list);
- list_del(&entry->list);
- memset(entry, 0, sizeof(*entry));
+ entry = __dma_entry_alloc();
#ifdef CONFIG_STACKTRACE
entry->stacktrace.max_entries = DMA_DEBUG_STACKTRACE_ENTRIES;
@@ -286,9 +300,6 @@ static struct dma_debug_entry *dma_entry_alloc(void)
entry->stacktrace.skip = 2;
save_stack_trace(&entry->stacktrace);
#endif
- num_free_entries -= 1;
- if (num_free_entries < min_free_entries)
- min_free_entries = num_free_entries;
out:
spin_unlock_irqrestore(&free_entries_lock, flags);
@@ -310,6 +321,53 @@ static void dma_entry_free(struct dma_debug_entry *entry)
spin_unlock_irqrestore(&free_entries_lock, flags);
}
+int dma_debug_resize_entries(u32 num_entries)
+{
+ int i, delta, ret = 0;
+ unsigned long flags;
+ struct dma_debug_entry *entry;
+ LIST_HEAD(tmp);
+
+ spin_lock_irqsave(&free_entries_lock, flags);
+
+ if (nr_total_entries < num_entries) {
+ delta = num_entries - nr_total_entries;
+
+ spin_unlock_irqrestore(&free_entries_lock, flags);
+
+ for (i = 0; i < delta; i++) {
+ entry = kzalloc(sizeof(*entry), GFP_KERNEL);
+ if (!entry)
+ break;
+
+ list_add_tail(&entry->list, &tmp);
+ }
+
+ spin_lock_irqsave(&free_entries_lock, flags);
+
+ list_splice(&tmp, &free_entries);
+ nr_total_entries += i;
+ num_free_entries += i;
+ } else {
+ delta = nr_total_entries - num_entries;
+
+ for (i = 0; i < delta && !list_empty(&free_entries); i++) {
+ entry = __dma_entry_alloc();
+ kfree(entry);
+ }
+
+ nr_total_entries -= i;
+ }
+
+ if (nr_total_entries != num_entries)
+ ret = 1;
+
+ spin_unlock_irqrestore(&free_entries_lock, flags);
+
+ return ret;
+}
+EXPORT_SYMBOL(dma_debug_resize_entries);
+
/*
* DMA-API debugging init code
*
@@ -490,6 +548,8 @@ void dma_debug_init(u32 num_entries)
return;
}
+ nr_total_entries = num_free_entries;
+
printk(KERN_INFO "DMA-API: debugging enabled by kernel config\n");
}
--
1.6.0.6
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