On Tue, 27 Jan 2015 00:52:12 +0300 Sergei Rogachev <rogachevser...@gmail.com>
wrote:
> Page owner uses the page_ext structure to keep meta-information
> for every page in the system. The structure also contains a field
> of type 'struct stack_trace', page owner uses this field during
> invocation of the function save_stack_trace. It is easy to notice
> that keeping a copy of this structure for every page in the system
> is very inefficiently in terms of memory.
>
> The patch removes this unnecessary field of page_ext and forces
> page owner to use a stack_trace structure allocated on the stack.
>
Fair enough.
What do you think of the below tweaks? Seems a bit neater, and it will
cause all unmentioned fields to be zeroed out. It's not a bug to leave
.max_entries uninitialised in print_page_owner(), but it's nice not to
leave loose ends.
--- a/mm/page_owner.c~mm-page_ext-remove-unnecessary-stack_trace-field-fix
+++ a/mm/page_owner.c
@@ -59,15 +59,14 @@ void __reset_page_owner(struct page *pag
void __set_page_owner(struct page *page, unsigned int order, gfp_t gfp_mask)
{
- struct page_ext *page_ext;
- struct stack_trace trace;
+ struct page_ext *page_ext = lookup_page_ext(page);
+ struct stack_trace trace = {
+ .nr_entries = 0,
+ .max_entries = ARRAY_SIZE(page_ext->trace_entries),
+ .entries = &page_ext->trace_entries[0],
+ .skip = 3,
+ };
- page_ext = lookup_page_ext(page);
-
- trace.nr_entries = 0;
- trace.max_entries = ARRAY_SIZE(page_ext->trace_entries);
- trace.entries = &page_ext->trace_entries[0];
- trace.skip = 3;
save_stack_trace(&trace);
page_ext->order = order;
@@ -83,8 +82,11 @@ print_page_owner(char __user *buf, size_
{
int ret;
int pageblock_mt, page_mt;
- struct stack_trace trace;
char *kbuf;
+ struct stack_trace trace = {
+ .nr_entries = page_ext->nr_entries,
+ .entries = &page_ext->trace_entries[0],
+ };
kbuf = kmalloc(count, GFP_KERNEL);
if (!kbuf)
@@ -122,9 +124,6 @@ print_page_owner(char __user *buf, size_
if (ret >= count)
goto err;
- trace.nr_entries = page_ext->nr_entries;
- trace.entries = &page_ext->trace_entries[0];
-
ret += snprint_stack_trace(kbuf + ret, count - ret, &trace, 0);
if (ret >= count)
goto err;
_
--
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