linux-kernel - Re: [PATCH v4 4/4] mm: introduce MADV

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Message-ID: <20190712150127.GV29483@dhcp22.suse.cz>
Date:   Fri, 12 Jul 2019 17:01:27 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     Minchan Kim <minchan@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>, linux-api@...r.kernel.org,
        Tim Murray <timmurray@...gle.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Daniel Colascione <dancol@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Sonny Rao <sonnyrao@...gle.com>, oleksandr@...hat.com,
        hdanton@...a.com, lizeb@...gle.com,
        Dave Hansen <dave.hansen@...el.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH v4 4/4] mm: introduce MADV_PAGEOUT

On Fri 12-07-19 09:58:09, Johannes Weiner wrote:
[...]
> > @@ -423,6 +445,12 @@ static int madvise_cold_pte_range(pmd_t *pmd, unsigned long addr,
> >  
> >  		VM_BUG_ON_PAGE(PageTransCompound(page), page);
> >  
> > +		if (pageout) {
> > +			if (isolate_lru_page(page))
> > +				continue;
> > +			list_add(&page->lru, &page_list);
> > +		}
> > +
> >  		if (pte_young(ptent)) {
> >  			ptent = ptep_get_and_clear_full(mm, addr, pte,
> >  							tlb->fullmm);
> 
> One thought on the ordering here.
> 
> When LRU isolation fails, it would still make sense to clear the young
> bit: we cannot reclaim the page as we wanted to, but the user still
> provided a clear hint that the page is cold and she won't be touching
> it for a while. MADV_PAGEOUT is basically MADV_COLD + try_to_reclaim.
> So IMO isolation should go to the end next to deactivate_page().

Make sense to me

-- 
Michal Hocko
SUSE Labs