Madhavan Srinivasan wrote:
On Tuesday 20 May 2014 03:57 PM, Kirill A. Shutemov wrote:
quoted
Rusty Russell wrote:
quoted
"Kirill A. Shutemov" [off-list ref] writes:
quoted
Andrew Morton wrote:
quoted
On Mon, 19 May 2014 16:23:07 -0700 (PDT) Hugh Dickins [off-list ref] wrote:
quoted
Shouldn't FAULT_AROUND_ORDER and fault_around_order be changed to be
the order of the fault-around size in bytes, and fault_around_pages()
use 1UL << (fault_around_order - PAGE_SHIFT)
Yes. And shame on me for missing it (this time!) at review.
There's still time to fix this. Patches, please.
Here it is. Made at 3.30 AM, build tested only.
Prefer on top of Maddy's patch which makes it always a variable, rather
than CONFIG_DEBUG_FS. It's got enough hair as it is.
Something like this?
From: "Kirill A. Shutemov" <redacted>
Date: Tue, 20 May 2014 13:02:03 +0300
Subject: [PATCH] mm: nominate faultaround area in bytes rather then page order
There are evidences that faultaround feature is less relevant on
architectures with page size bigger then 4k. Which makes sense since
page fault overhead per byte of mapped area should be less there.
Let's rework the feature to specify faultaround area in bytes instead of
page order. It's 64 kilobytes for now.
The patch effectively disables faultaround on architectures with
page size >= 64k (like ppc64).
It's possible that some other size of faultaround area is relevant for a
platform. We can expose `fault_around_bytes' variable to arch-specific
code once such platforms will be found.
Signed-off-by: Kirill A. Shutemov <redacted>
---
mm/memory.c | 62 +++++++++++++++++++++++--------------------------------------
1 file changed, 23 insertions(+), 39 deletions(-)
diff --git a/mm/memory.c b/mm/memory.c
index 037b812a9531..252b319e8cdf 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3402,63 +3402,47 @@ void do_set_pte(struct vm_area_struct *vma, unsigned long address,
update_mmu_cache(vma, address, pte);
}
-#define FAULT_AROUND_ORDER 4
+static unsigned long fault_around_bytes = 65536;
+
+static inline unsigned long fault_around_pages(void)
+{
+ return rounddown_pow_of_two(fault_around_bytes) / PAGE_SIZE;
+}
+
+static inline unsigned long fault_around_mask(void)
+{
+ return ~(rounddown_pow_of_two(fault_around_bytes) - 1) & PAGE_MASK;
+}
-#ifdef CONFIG_DEBUG_FS
-static unsigned int fault_around_order = FAULT_AROUND_ORDER;
-static int fault_around_order_get(void *data, u64 *val)
+#ifdef CONFIG_DEBUG_FS
+static int fault_around_bytes_get(void *data, u64 *val)
{
- *val = fault_around_order;
+ *val = fault_around_bytes;
return 0;
}
-static int fault_around_order_set(void *data, u64 val)
+static int fault_around_bytes_set(void *data, u64 val)
{
Kindly ignore the question if not relevant. Even though we need root
access to alter the value, will we be fine with
negative value?.
val is u64. or I miss something?
--
Kirill A. Shutemov