I just spotted this in /proc/meminfo on an old Core2 machine with 4G.
DirectMap2M: 18446744073709543424 kB
Looks like we subtracted 8192 from 0 somewhere.
Should split_page_count() be checking that direct_pages_count > 0 ?

Ok, this diff makes that number print out as 0.

If this looks ok, I'll submit it properly, though I'd like to better understand what's happening here. Shouldn't I have 2M pages ?

Dave

arch/x86/mm/pageattr.c +3 -0

index a3137a4feed1..ff0e0c6c350e 100644
@@ -66,6 +66,9 @@ void update_page_count(int level, unsigned long pages)
 
 static void split_page_count(int level)
 {
+	if (direct_pages_count[level] == 0)
+		return;
+
 	direct_pages_count[level]--;
 	direct_pages_count[level - 1] += PTRS_PER_PTE;
 }

Dave Jones

author

2016-01-07 00:18 UTC #2 lore raw

Quoted 5 lines · Dave Jones

Quoted 4 lines · Dave Jones
I just spotted this in /proc/meminfo on an old Core2 machine with 4G.
DirectMap2M: 18446744073709543424 kB

Quoted 8 lines

Quoted 3 lines
Looks like we subtracted 8192 from 0 somewhere.
Should split_page_count() be checking that direct_pages_count > 0 ?
Ok, this diff makes that number print out as 0.
If this looks ok, I'll submit it properly, though I'd like to better understand what's happening here. Shouldn't I have 2M pages ?

Ah. We disable them when compiling with DEBUG_PAGEALLOC.
So this is only needed in that case.
If people think it's worth an ifdef for those two added lines I'll add it, but it seems pretty benign to just always check.

thoughts?

Dave

Thomas Gleixner

2016-01-11 08:58 UTC #3 lore raw

Quoted 12 lines · Dave Jones

Quoted 11 lines · Dave Jones
Quoted 7 lines · Dave Jones
I just spotted this in /proc/meminfo on an old Core2 machine with 4G.
DirectMap2M: 18446744073709543424 kB
Looks like we subtracted 8192 from 0 somewhere.
Should split_page_count() be checking that direct_pages_count > 0 ?
Ok, this diff makes that number print out as 0.

Quoted 7 lines

Quoted 2 lines
If this looks ok, I'll submit it properly, though I'd like to better understand what's happening here. Shouldn't I have 2M pages ?
Ah. We disable them when compiling with DEBUG_PAGEALLOC.
So this is only needed in that case.
If people think it's worth an ifdef for those two added lines I'll add it, but it seems pretty benign to just always check.

Agreed.

tglx