linux-kernel - Re: [PATCH RESEND 1/2] mm: swap: clean up swap readahead

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Date:   Fri, 23 Feb 2018 16:02:27 +0800
From:   "Huang\, Ying" <ying.huang@...el.com>
To:     <minchan@...nel.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        lkml <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>, Hugh Dickins <hughd@...gle.com>
Subject: Re: [PATCH RESEND 1/2] mm: swap: clean up swap readahead

<minchan@...nel.org> writes:
[snip]

> diff --git a/mm/swap_state.c b/mm/swap_state.c
> index 39ae7cfad90f..c56cce64b2c3 100644
> --- a/mm/swap_state.c
> +++ b/mm/swap_state.c
> @@ -332,32 +332,38 @@ struct page *lookup_swap_cache(swp_entry_t entry, struct vm_area_struct *vma,
>  			       unsigned long addr)
>  {
>  	struct page *page;
> -	unsigned long ra_info;
> -	int win, hits, readahead;
>  
>  	page = find_get_page(swap_address_space(entry), swp_offset(entry));
>  
>  	INC_CACHE_INFO(find_total);
>  	if (page) {
> +		bool vma_ra = swap_use_vma_readahead();
> +		bool readahead = TestClearPageReadahead(page);
> +

TestClearPageReadahead() cannot be called for compound page.  As in

PAGEFLAG(Readahead, reclaim, PF_NO_COMPOUND)
	TESTCLEARFLAG(Readahead, reclaim, PF_NO_COMPOUND)

>  		INC_CACHE_INFO(find_success);
>  		if (unlikely(PageTransCompound(page)))
>  			return page;
> -		readahead = TestClearPageReadahead(page);

So we can only call it here after checking whether page is compound.

Best Regards,
Huang, Ying

> -		if (vma) {
> -			ra_info = GET_SWAP_RA_VAL(vma);
> -			win = SWAP_RA_WIN(ra_info);
> -			hits = SWAP_RA_HITS(ra_info);
> +
> +		if (vma && vma_ra) {
> +			unsigned long ra_val;
> +			int win, hits;
> +
> +			ra_val = GET_SWAP_RA_VAL(vma);
> +			win = SWAP_RA_WIN(ra_val);
> +			hits = SWAP_RA_HITS(ra_val);
>  			if (readahead)
>  				hits = min_t(int, hits + 1, SWAP_RA_HITS_MAX);
>  			atomic_long_set(&vma->swap_readahead_info,
>  					SWAP_RA_VAL(addr, win, hits));
>  		}
> +
>  		if (readahead) {
>  			count_vm_event(SWAP_RA_HIT);
> -			if (!vma)
> +			if (!vma || !vma_ra)
>  				atomic_inc(&swapin_readahead_hits);
>  		}
>  	}
> +
>  	return page;
>  }
>

[snip]