linux-kernel - [RFC] mm: direct mapping count in /proc/meminfo is error

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Date:	Fri, 20 Nov 2015 16:17:12 +0800
From:	Xishi Qiu <qiuxishi@...wei.com>
To:	Andrew Morton <akpm@...ux-foundation.org>,
	Tang Chen <tangchen@...fujitsu.com>,
	zhong jiang <zhongjiang@...wei.com>,
	Minchan Kim <minchan@...nel.org>, Mel Gorman <mgorman@...e.de>
CC:	Linux MM <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>
Subject: [RFC] mm: direct mapping count in /proc/meminfo is error

I find the direct mapping count in /proc/meminfo is error. 
The value should be equal to the size of init_memory_mapping which
showed in boot log. 

I add some print to show direct_pages_count[] immediately after
init_memory_mapping(). The reason is that we double counting.

Here is the log(kernel v4.4):
...
[    0.000000] init_memory_mapping: [mem 0x00000000-0x000fffff]  // called from "init_memory_mapping(0, ISA_END_ADDRESS);"
[    0.000000]  [mem 0x00000000-0x000fffff] page 4k
[    0.000000] BRK [0x01ebf000, 0x01ebffff] PGTABLE
[    0.000000] BRK [0x01ec0000, 0x01ec0fff] PGTABLE
[    0.000000] BRK [0x01ec1000, 0x01ec1fff] PGTABLE
[    0.000000] init_memory_mapping: [mem 0xc3fe00000-0xc3fffffff]  // called from "memory_map_top_down(ISA_END_ADDRESS, end);"
[    0.000000]  [mem 0xc3fe00000-0xc3fffffff] page 1G  // increase count of PG_LEVEL_1G in c00000000(48G)-c3fffffff(49G) one time
[    0.000000] init_memory_mapping: [mem 0xc20000000-0xc3fdfffff]
[    0.000000]  [mem 0xc20000000-0xc3fdfffff] page 1G  // increase count of PG_LEVEL_1G in c00000000(48G)-c3fffffff(49G) two time
[    0.000000] init_memory_mapping: [mem 0x00100000-0xbf78ffff]
[    0.000000]  [mem 0x00100000-0x001fffff] page 4k
[    0.000000]  [mem 0x00200000-0x3fffffff] page 2M
[    0.000000]  [mem 0x40000000-0x7fffffff] page 1G
[    0.000000]  [mem 0x80000000-0xbf5fffff] page 2M
[    0.000000]  [mem 0xbf600000-0xbf78ffff] page 4k
[    0.000000] init_memory_mapping: [mem 0x100000000-0xc1fffffff]
[    0.000000]  [mem 0x100000000-0xc1fffffff] page 1G  // increase count of PG_LEVEL_1G in c00000000(48G)-c3fffffff(49G) three time
...
[    0.000000] DirectMap4k:        3648 kB
[    0.000000] DirectMap2M:     2084864 kB
[    0.000000] DirectMap1G:    50331648 kB

euler-linux:~ # cat /proc/meminfo | grep DirectMap
DirectMap4k:       91712 kB
DirectMap2M:     4093952 kB
DirectMap1G:    48234496 kB


total DirectMap is 48234496 + 4093952 + 91712 = 52420160kb
		    50331648 + 2084864 + 3648 = 52420160kb
total init_memory_mapping is 50323008kb

52420160kb - 50323008kb = 2097152kb = 2G

However I haven't find a better way to fix it, any ideas?

Thanks,
Xishi Qiu


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