On 08/10/2016 08:16 AM, js1304@xxxxxxxxx wrote:
From: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Until now, if some page_ext users want to use it's own field on page_ext,
it should be defined in struct page_ext by hard-coding. It has a problem
that wastes memory in following situation.
struct page_ext {
#ifdef CONFIG_A
int a;
#endif
#ifdef CONFIG_B
int b;
#endif
};
Assume that kernel is built with both CONFIG_A and CONFIG_B.
Even if we enable feature A and doesn't enable feature B at runtime,
each entry of struct page_ext takes two int rather than one int.
It's undesirable result so this patch tries to fix it.
To solve above problem, this patch implements to support extra space
allocation at runtime. When need() callback returns true, it's extra
memory requirement is summed to entry size of page_ext. Also, offset
for each user's extra memory space is returned. With this offset,
user can use this extra space and there is no need to define needed
field on page_ext by hard-coding.
This patch only implements an infrastructure. Following patch will use it
for page_owner which is only user having it's own fields on page_ext.
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
Fine, but...
static void __init invoke_init_callbacks(void)
@@ -91,6 +102,16 @@ static void __init invoke_init_callbacks(void)
}
}
+static unsigned long get_entry_size(void)
+{
+ return sizeof(struct page_ext) + extra_mem;
+}
+
+static inline struct page_ext *get_entry_base(void *base, unsigned long offset)
+{
+ return base + get_entry_size() * offset;
+}
Why _base()? Why not just get_entry?
Also I find it confusing that the word offset here is different than the
offset in page_ext_operations. Maybe use "index" instead?
Vlastimil
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