From: Minchan Kim <minchan@kernel.org>
Date: Fri, 14 Oct 2016 22:46:04 +0900
To: Michal Hocko <mhocko@kernel.org>
Cc: Ming Ling <ming.ling@spreadtrum.com>, akpm@linux-foundation.org,
        mgorman@techsingularity.net, vbabka@suse.cz, hannes@cmpxchg.org,
        baiyaowei@cmss.chinamobile.com, iamjoonsoo.kim@lge.com,
        minchan@kernel.org, rientjes@google.com, hughd@google.com,
        kirill.shutemov@linux.intel.com, riel@redhat.com, mgorman@suse.de,
        aquini@redhat.com, corbet@lwn.net, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, orson.zhai@spreadtrum.com,
        geng.ren@spreadtrum.com, chunyan.zhang@spreadtrum.com,
        zhizhou.tian@spreadtrum.com, yuming.han@spreadtrum.com,
        xiajing@spreadst.com
Subject: Re: [PATCH v2] mm: exclude isolated non-lru pages from
 NR_ISOLATED_ANON or NR_ISOLATED_FILE.
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 <20161014083219.GA20260@spreadtrum.com>
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Hi, Michal,

On Fri, Oct 14, 2016 at 01:30:44PM +0200, Michal Hocko wrote:

< snip>

> > void putback_movable_pages(struct list_head *l)
> > {
> > 	......
> > 	/*
> > 	 * We isolated non-lru movable page so here we can use
> >  	 * __PageMovable because LRU page's mapping cannot have
> > 	 * PAGE_MAPPING_MOVABLE.
> > 	 */
> > 	if (unlikely(__PageMovable(page))) {
> > 		VM_BUG_ON_PAGE(!PageIsolated(page), page);
> > 		lock_page(page);
> > 		if (PageMovable(page))
> > 			putback_movable_page(page);
> > 		else
> > 			__ClearPageIsolated(page);
> > 		unlock_page(page);
> > 		put_page(page);
> > 	} else {
> > 		putback_lru_page(page);
> > 	}
> > }
> 
> I am not familiar with this code enough to comment but to me it all
> sounds quite subtle.

It was due to lacking of page flags on 32bit machine, sadly.
Better idea is always welcome.

> 
> > > Why don't you simply mimic what shrink_inactive_list does? Aka count the
> > > number of isolated pages and then account them when appropriate?
> > >
> > I think i am correcting clearly wrong part. So, there is no need to
> > describe it too detailed. It's a misunderstanding, and i will add
> > more comments as you suggest.
> 
> OK, so could you explain why you prefer to relyon __PageMovable rather
> than do a trivial counting during the isolation?

I don't get it. Could you elaborate it a bit more?

> -- 
> Michal Hocko
> SUSE Labs