Re: [PATCH 1/3] mm, page_owner: record page owner for each subpage

[Vlastimil Babka <vbabka@suse.cz>]

On 8/16/19 4:04 PM, Kirill A. Shutemov wrote:
> On Fri, Aug 16, 2019 at 12:13:59PM +0200, Vlastimil Babka wrote:
>> Currently, page owner info is only recorded for the first page of a high-order
>> allocation, and copied to tail pages in the event of a split page. With the
>> plan to keep previous owner info after freeing the page, it would be benefical
>> to record page owner for each subpage upon allocation. This increases the
>> overhead for high orders, but that should be acceptable for a debugging option.
>>
>> The order stored for each subpage is the order of the whole allocation. This
>> makes it possible to calculate the "head" pfn and to recognize "tail" pages
>> (quoted because not all high-order allocations are compound pages with true
>> head and tail pages). When reading the page_owner debugfs file, keep skipping
>> the "tail" pages so that stats gathered by existing scripts don't get inflated.
>>
>> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
> 
> Hm. That's all reasonable, but I have a question: do you see how page
> owner thing works for THP now?
> 
> I don't see anything in split_huge_page() path (do not confuse it with
> split_page() path) that would copy the information to tail pages. Do you?
 
You're right, it's missing. This patch fixes that and can be added e.g.
at the end of the series.

----8<----
From 56ac1b41559eecf52a2d453c49ce66dbbb227c64 Mon Sep 17 00:00:00 2001
From: Vlastimil Babka <vbabka@suse.cz>
Date: Mon, 19 Aug 2019 13:38:29 +0200
Subject: [PATCH] mm, page_owner: handle THP splits correctly

THP splitting path is missing the split_page_owner() call that split_page()
has. As a result, split THP pages are wrongly reported in the page_owner file
as order-9 pages. Furthermore when the former head page is freed, the remaining
former tail pages are not listed in the page_owner file at all. This patch
fixes that by adding the split_page_owner() call into __split_huge_page().

Reported-by: Kirill A. Shutemov <kirill@shutemov.name>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
---
 mm/huge_memory.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 738065f765ab..d727a0401484 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -32,6 +32,7 @@
 #include <linux/shmem_fs.h>
 #include <linux/oom.h>
 #include <linux/numa.h>
+#include <linux/page_owner.h>
 
 #include <asm/tlb.h>
 #include <asm/pgalloc.h>
@@ -2533,6 +2534,8 @@ static void __split_huge_page(struct page *page, struct list_head *list,
 
 	remap_page(head);
 
+	split_page_owner(head, HPAGE_PMD_ORDER);
+
 	for (i = 0; i < HPAGE_PMD_NR; i++) {
 		struct page *subpage = head + i;
 		if (subpage == page)
-- 
2.22.0