Re: [PATCH] mm, swap: VMA based swap readahead

["Huang\, Ying" <ying.huang@intel.com>]

Hi, Tim,

Tim Chen <tim.c.chen@linux.intel.com> writes:

> 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?

I don't call put_page() here because the page will be mapped to process
page table.

> 		put_page(fpage);
>
> I think there is no put_page on the returned page when you return from
> do_swap_page_readahead.

In the original swapin_readahead(), the read_swap_cache_async() will be
called for the fault swap entry again in the end of the function, and
pug_page() is not called there.

Best Regards,
Huang, Ying

> 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;

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