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Sender: Minchan Kim <minchan.kim@gmail.com>
Date:   Wed, 18 Jan 2023 09:15:34 -0800
From:   Minchan Kim <minchan@kernel.org>
To:     Michal Hocko <mhocko@suse.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Suren Baghdasaryan <surenb@google.com>,
        Matthew Wilcox <willy@infradead.org>,
        linux-mm <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>,
        SeongJae Park <sj@kernel.org>
Subject: Re: [PATCH 3/3] mm: add vmstat statistics for madvise_[cold|pageout]
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References: <20230117231632.2734737-1-minchan@kernel.org>
 <20230117231632.2734737-3-minchan@kernel.org>
 <Y8e30ujUGLwDfes8@dhcp22.suse.cz>
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On Wed, Jan 18, 2023 at 10:11:46AM +0100, Michal Hocko wrote:
> On Tue 17-01-23 15:16:32, Minchan Kim wrote:
> > madvise LRU manipulation APIs need to scan address ranges to find
> > present pages at page table and provides advice hints for them.
> > 
> > Likewise pg[scan/steal] count on vmstat, madvise_pg[scanned/hinted]
> > shows the proactive reclaim efficiency so this patch addes those
> > two statistics in vmstat.
> 
> Please describe the usecase for those new counters.

I wanted to know the proactive reclaim efficieny using MADV_COLD/MDDV_PAGEOUT.
Userspace has several policy which when/which vmas need to be hinted by the call
and they are evolving. I needed to know how effectively their policy works since
the vma ranges are huge(i.e., nr_hinted/nr_scanned).