Re: [PATCH] mm/swap_state: Skip meaningless swap cache readahead when ra_info.win == 0

[linmiaohe]

Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Fri, 9 Oct 2020 09:30:59 -0400 Miaohe Lin <linmiaohe@xxxxxxxxxx> wrote:
>
>> swap_ra_info() may leave ra_info untouched in non_swap_entry() case as 
>> page table lock is not held. In this case, we have ra_info.nr_pte == 0 
>> and it is meaningless to continue with swap cache readahead. Skip such 
>> ops by init ra_info.win = 1.
>> 
>
>Looks right.  But I think it would be better to fix this in
>swap_ra_info() - make it more consistent in its return state.
>

I think modernify the struct initializer is better because it means we have to swap in one page at least.
Many thanks.

>Otherwise, let's modernify that struct initializer:
>
>--- a/mm/swap_state.c~mm-swap_state-skip-meaningless-swap-cache-readahead-when-ra_infowin-==-0-fix
>+++ a/mm/swap_state.c
>@@ -839,7 +839,9 @@ static struct page *swap_vma_readahead(s
> 	swp_entry_t entry;
> 	unsigned int i;
> 	bool page_allocated;
>-	struct vma_swap_readahead ra_info = {1,};
>+	struct vma_swap_readahead ra_info = {
>+		.win = 1,
>+	};
> 
> 	swap_ra_info(vmf, &ra_info);
> 	if (ra_info.win == 1)
>_
>