linux-kernel - Re: why the count nr_file_pages is not equal to nr_inactive_file + nr_active

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Date:	Fri, 13 May 2016 15:00:58 +0800
From:	Aaron Lu <aaron.lu@...el.com>
To:	Xishi Qiu <qiuxishi@...wei.com>, Linux MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: why the count nr_file_pages is not equal to nr_inactive_file +
 nr_active_file ?

On 05/13/2016 11:58 AM, Xishi Qiu wrote:
> I find the count nr_file_pages is not equal to nr_inactive_file + nr_active_file.
> There are 8 cpus, 2 zones in my system.
> 
> I think may be the pagevec trigger the problem, but PAGEVEC_SIZE is only 14.
> Does anyone know the reason?

One thing I can see is the ram backed filesystem where the page is
counted as NR_FILE_PAGE but go into the anonymous LRU list instead of
the file LRU list.

See function shmem_getpage_gfp.

An example:
[aaron@...onlu ~]$ head -11 /proc/vmstat 
nr_free_pages 194472
nr_alloc_batch 58
nr_inactive_anon 483386
nr_active_anon 298161
nr_inactive_file 452791
nr_active_file 1942376
nr_unevictable 84
nr_mlock 84
nr_anon_pages 445332
nr_mapped 93553
nr_file_pages 2731481
[aaron@...onlu ~]$ fallocate -l 400M /dev/shm/test
[aaron@...onlu ~]$ head -11 /proc/vmstat 
nr_free_pages 94808
nr_alloc_batch 838
nr_inactive_anon 582385
nr_active_anon 298371
nr_inactive_file 452795
nr_active_file 1942380
nr_unevictable 84
nr_mlock 84
nr_anon_pages 445543
nr_mapped 93658
nr_file_pages 2830488

The nr_file_pages increased with nr_inactive_anon while the
nr_{in}active_file don't see much change.

Regards,
Aaron

> 
> Thanks,
> Xishi Qiu
> 
> root@...650:/ # cat /proc/vmstat 
> nr_free_pages 54192
> nr_inactive_anon 39830
> nr_active_anon 28794
> nr_inactive_file 432444
> nr_active_file 20659
> nr_unevictable 2363
> nr_mlock 0
> nr_anon_pages 65249
> nr_mapped 19742
> nr_file_pages 462723
> nr_dirty 20
> nr_writeback 0
> ...
> 
> 
> nr_inactive_file 432444
> nr_active_file 20659
> total is 453103
> 
> nr_file_pages 462723
> 
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