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From: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
To: Wu Fengguang <fengguang.wu@intel.com>
Subject: Re: [PATCH 1/4] Properly account for the number of page cache pages zone_reclaim() can reclaim
Cc: kosaki.motohiro@jp.fujitsu.com, Mel Gorman <mel@csn.ul.ie>,
       Rik van Riel <riel@redhat.com>,
       Christoph Lameter <cl@linux-foundation.org>,
       "Zhang, Yanmin" <yanmin.zhang@intel.com>,
       "linuxram@us.ibm.com" <linuxram@us.ibm.com>,
       linux-mm <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>
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> We are not talking about NR_TMPFS_PAGES, but NR_TMPFS_MAPPED :)
> 
> We only need to account it in page_add_file_rmap() and page_remove_rmap(),
> I don't think they are too hot paths. And the relative cost is low enough.
> 
> It will look like this.
> 
> ---
>  include/linux/mmzone.h |    1 +
>  mm/rmap.c              |    4 ++++
>  2 files changed, 5 insertions(+)
> 
> --- linux.orig/include/linux/mmzone.h
> +++ linux/include/linux/mmzone.h
> @@ -99,6 +99,7 @@ enum zone_stat_item {
>  	NR_VMSCAN_WRITE,
>  	/* Second 128 byte cacheline */
>  	NR_WRITEBACK_TEMP,	/* Writeback using temporary buffers */
> +	NR_TMPFS_MAPPED,
>  #ifdef CONFIG_NUMA
>  	NUMA_HIT,		/* allocated in intended node */
>  	NUMA_MISS,		/* allocated in non intended node */
> --- linux.orig/mm/rmap.c
> +++ linux/mm/rmap.c
> @@ -844,6 +844,8 @@ void page_add_file_rmap(struct page *pag
>  {
>  	if (atomic_inc_and_test(&page->_mapcount)) {
>  		__inc_zone_page_state(page, NR_FILE_MAPPED);
> +		if (PageSwapBacked(page))
> +			__inc_zone_page_state(page, NR_TMPFS_MAPPED);
>  		mem_cgroup_update_mapped_file_stat(page, 1);
>  	}
>  }
> @@ -894,6 +896,8 @@ void page_remove_rmap(struct page *page)
>  			mem_cgroup_uncharge_page(page);
>  		__dec_zone_page_state(page,
>  			PageAnon(page) ? NR_ANON_PAGES : NR_FILE_MAPPED);
> +		if (!PageAnon(page) && PageSwapBacked(page))
> +			__dec_zone_page_state(page, NR_TMPFS_MAPPED);
>  		mem_cgroup_update_mapped_file_stat(page, -1);
>  		/*
>  		 * It would be tidy to reset the PageAnon mapping here,

I think this patch looks good. thanks :)

but I have one request. 
Could you please rename NR_FILE_MAPPED to NR_SWAP_BACKED_FILE_MAPPED?

I mean, mm/shmem isn't only used for tmpfs, but also be used ipc/shm and
/dev/zero.
NR_TMPFS_MAPPED seems a bit misleading.