On 2020-06-29 08:19, Matthew Wilcox (Oracle) wrote:
Tail page flags contain very little useful information. Print the head
page's flags instead (even though PageHead is a little misleading).
You are right about the tail page. And the raw output provides the tail
page flags, in case someone *really* needs to dig into tail page problems,
so that's all good.
However, I just gave this a spin, and seeing the "|head" in the list for
my "tail page: dump_page test" is also slightly misleading for me, too.
Sure, one can eventually work through it and conclude "my dump_page output
is misleading", but I think a small tweak would avoid that:
Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
---
mm/debug.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/debug.c b/mm/debug.c
index 4f376514744d..44d843b3b07c 100644
--- a/mm/debug.c
+++ b/mm/debug.c
@@ -163,7 +163,7 @@ void __dump_page(struct page *page, const char *reason)
out_mapping:
BUILD_BUG_ON(ARRAY_SIZE(pageflag_names) != __NR_PAGEFLAGS + 1);
- pr_warn("%sflags: %#lx(%pGp)%s\n", type, page->flags, &page->flags,
+ pr_warn("%sflags: %#lx(%pGp)%s\n", type, head->flags, &head->flags,
page_cma ? " CMA" : "");
Perhaps just adding "head " to the above will clear it all up:
diff --git a/mm/debug.c b/mm/debug.c
index fcf3a16902b2..b7ac8af71940 100644
--- a/mm/debug.c
+++ b/mm/debug.c
@@ -165,7 +165,7 @@ void __dump_page(struct page *page, const char *reason)
out_mapping:
BUILD_BUG_ON(ARRAY_SIZE(pageflag_names) != __NR_PAGEFLAGS + 1);
- pr_warn("%sflags: %#lx(%pGp)%s\n", type, head->flags, &head->flags,
+ pr_warn("head %sflags: %#lx(%pGp)%s\n", type, head->flags, &head->flags,
page_cma ? " CMA" : "");
hex_only:
Sample output:
[ 62.064271] page:000000001c8f0c3e refcount:513 mapcount:1 mapping:0000000000000000 index:0x11
head:00000000ba9ccef2 order:9 compound_mapcount:1 compound_pincount:512
[ 62.078432] head anon flags: 0x17ffe000001000e(referenced|uptodate|dirty|head)
[ 62.088454] raw: 017ffe0000000000 ffffea00209e8001 ffffea00209e8448 dead000000000400
[ 62.095356] raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
[ 62.102289] head: 017ffe000001000e ffffffff83649ca0 ffffea00209e0008 ffff88889663c001
[ 62.109286] head: 0000000000000000 0000000000000000 00000201ffffffff 0000000000000000
[ 62.116301] page dumped because: gup_benchmark: tail page: dump_page test
thanks,
--
John Hubbard
NVIDIA
