On Wed, Aug 31, 2022 at 10:46 AM Kent Overstreet
[off-list ref] wrote:

On Wed, Aug 31, 2022 at 11:11:03AM +0100, Mel Gorman wrote:

quoted

On Tue, Aug 30, 2022 at 02:48:59PM -0700, Suren Baghdasaryan wrote:

quoted

Redefine alloc_pages, __get_free_pages to record allocations done by
these functions. Instrument deallocation hooks to record object freeing.

Signed-off-by: Suren Baghdasaryan <surenb@google.com>
+#ifdef CONFIG_PAGE_ALLOC_TAGGING
+
 #include <linux/alloc_tag.h>
 #include <linux/page_ext.h>

@@ -25,4 +27,37 @@ static inline void pgalloc_tag_dec(struct page *page, unsigned int order)
            alloc_tag_sub(get_page_tag_ref(page), PAGE_SIZE << order);
 }

+/*
+ * Redefinitions of the common page allocators/destructors
+ */
+#define pgtag_alloc_pages(gfp, order)                                      \
+({                                                                 \
+   struct page *_page = _alloc_pages((gfp), (order));              \
+                                                                   \
+   if (_page)                                                      \
+           alloc_tag_add(get_page_tag_ref(_page), PAGE_SIZE << (order));\
+   _page;                                                          \
+})
+

Instead of renaming alloc_pages, why is the tagging not done in
__alloc_pages()? At least __alloc_pages_bulk() is also missed. The branch
can be guarded with IS_ENABLED.

It can't be in a function, it has to be in a wrapper macro.

Ah, right. __FILE__, __LINE__ and others we use to record the call
location would point to include/linux/gfp.h instead of the location
allocation is performed at.

alloc_tag_add() is a macro that defines a static struct in a special elf
section. That struct holds the allocation counters, and putting it in a special
elf section is how the code to list it in debugfs finds it.

Look at the dynamic debug code for prior precedence for this trick in the kernel
- that's how it makes pr_debug() calls dynamically controllable at runtime, from
debugfs. We're taking that method and turning it into a proper library.

Because all the counters are statically allocated, without even a pointer deref
to get to them in the allocation path (one pointer deref to get to them in the
deallocate path), that makes this _much, much_ cheaper than anything that could
be done with tracing - cheap enough that I expect many users will want to enable
it in production.

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