linux-kernel - Re: [PATCH 2/2] mm/madvise: skip MADV_PAGEOUT on shared swap cache pages

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Date:   Thu, 26 Mar 2020 23:42:44 -0700
From:   Minchan Kim <minchan@...nel.org>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        linux-kernel@...r.kernel.org, mhocko@...e.com, jannh@...gle.com,
        vbabka@...e.cz, dancol@...gle.com, joel@...lfernandes.org,
        akpm@...ux-foundation.org
Subject: Re: [PATCH 2/2] mm/madvise: skip MADV_PAGEOUT on shared swap cache
 pages

On Thu, Mar 26, 2020 at 04:00:09PM -0700, Dave Hansen wrote:
> On 3/25/20 11:28 PM, Minchan Kim wrote:
> >> diff -puN mm/madvise.c~madv-pageout-ignore-shared-swap-cache mm/madvise.c
> >> --- a/mm/madvise.c~madv-pageout-ignore-shared-swap-cache	2020-03-23 16:30:52.022385888 -0700
> >> +++ b/mm/madvise.c	2020-03-23 16:41:15.448384333 -0700
> >> @@ -261,6 +261,7 @@ static struct page *pte_get_reclaim_page
> >>  {
> >>  	swp_entry_t entry;
> >>  	struct page *page;
> >> +	int nr_page_references = 0;
> > nit: just 'referenced' would be enough.
> 
> I guess I could track one bit like that.  But, it would require checking
> both page_mapcount() and page_swapcount() for being >1.  This way, I
> just accumulate the count and have a check at a single place.
> 
> I think it ends up much simpler this way.

I meant the variable name. 'referenced' would be enough for indication
like rmap.c and khugepaged.c. Anyway, it's up to you.