linux-kernel - Re: [PATCH v1 4/4] mm: introduce MADV

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Date:   Tue, 4 Jun 2019 15:38:20 +0000
From:   Christopher Lameter <cl@...ux.com>
To:     Minchan Kim <minchan@...nel.org>
cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>, linux-api@...r.kernel.org,
        Michal Hocko <mhocko@...e.com>,
        Johannes Weiner <hannes@...xchg.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>,
        Brian Geffon <bgeffon@...gle.com>, jannh@...gle.com,
        oleg@...hat.com, christian@...uner.io, oleksandr@...hat.com,
        hdanton@...a.com
Subject: Re: [PATCH v1 4/4] mm: introduce MADV_PAGEOUT

On Mon, 3 Jun 2019, Minchan Kim wrote:

> @@ -415,6 +416,128 @@ static long madvise_cold(struct vm_area_struct *vma,
>  	return 0;
>  }
>
> +static int madvise_pageout_pte_range(pmd_t *pmd, unsigned long addr,
> +				unsigned long end, struct mm_walk *walk)
> +{
> +	pte_t *orig_pte, *pte, ptent;
> +	spinlock_t *ptl;
> +	LIST_HEAD(page_list);
> +	struct page *page;
> +	int isolated = 0;
> +	struct vm_area_struct *vma = walk->vma;
> +	unsigned long next;
> +
> +	if (fatal_signal_pending(current))
> +		return -EINTR;
> +
> +	next = pmd_addr_end(addr, end);
> +	if (pmd_trans_huge(*pmd)) {
> +		ptl = pmd_trans_huge_lock(pmd, vma);
> +		if (!ptl)
> +			return 0;
> +
> +		if (is_huge_zero_pmd(*pmd))
> +			goto huge_unlock;
> +
> +		page = pmd_page(*pmd);
> +		if (page_mapcount(page) > 1)
> +			goto huge_unlock;
> +
> +		if (next - addr != HPAGE_PMD_SIZE) {
> +			int err;
> +
> +			get_page(page);
> +			spin_unlock(ptl);
> +			lock_page(page);
> +			err = split_huge_page(page);
> +			unlock_page(page);
> +			put_page(page);
> +			if (!err)
> +				goto regular_page;
> +			return 0;
> +		}

I have seen this before multiple times. Is there a way to avoid
replicating the whole shebang?