linux-kernel - Re: [PATCH] mm, swap: VMA based swap readahead

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Date:   Sun, 19 Mar 2017 18:01:41 -0700
From:   Tim Chen <tim.c.chen@...ux.intel.com>
To:     "Huang, Ying" <ying.huang@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Shaohua Li <shli@...nel.org>, Rik van Riel <riel@...hat.com>,
        Ingo Molnar <mingo@...nel.org>, Michal Hocko <mhocko@...e.com>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Minchan Kim <minchan@...nel.org>,
        Dmitry Safonov <dsafonov@...tuozzo.com>,
        Mark Rutland <mark.rutland@....com>,
        Vegard Nossum <vegard.nossum@...cle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Johannes Weiner <hannes@...xchg.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Jan Kara <jack@...e.cz>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Lorenzo Stoakes <lstoakes@...il.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Hugh Dickins <hughd@...gle.com>,
        Gerald Schaefer <gerald.schaefer@...ibm.com>,
        Aaron Lu <aaron.lu@...el.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH] mm, swap: VMA based swap readahead

On Tue, Mar 14, 2017 at 05:25:29PM +0800, Huang, Ying wrote:
> +struct page *do_swap_page_readahead(struct vm_fault *vmf,
> +				    struct vma_swap_readahead *swap_ra,
> +				    swp_entry_t fentry,
> +				    struct page *fpage)
> +{
> +	struct blk_plug plug;
> +	struct vm_area_struct *vma = vmf->vma;
> +	struct page *page;
> +	unsigned long addr;
> +	pte_t *pte, pentry;
> +	gfp_t gfp_mask;
> +	swp_entry_t entry;
> +	int i, alloc = 0, count;
> +	bool page_allocated;
> +
> +	addr = vmf->address & PAGE_MASK;
> +	blk_start_plug(&plug);
> +	if (!fpage) {
> +		fpage = __read_swap_cache_async(fentry, GFP_HIGHUSER_MOVABLE,
> +						vma, addr, &page_allocated);
> +		if (!fpage) {
> +			blk_finish_plug(&plug);
> +			return NULL;
> +		}
> +		if (page_allocated) {
> +			alloc++;
> +			swap_readpage(fpage);
> +		}

Do you need to add here a put_page as there's a get_page
in __read-swap_cache_async?

		put_page(fpage);

I think there is no put_page on the returned page when you return from
do_swap_page_readahead.

Thanks.

Tim

> +	}
> +	/* fault page has been checked */
> +	count = 1;
> +	addr += PAGE_SIZE * swap_ra->direction;
> +	pte = swap_ra->ptes;
> +	if (swap_ra->direction < 0)
> +		pte += swap_ra->nr_pte - 1;