Re: [patch v3] swap: virtual swap readahead

KAMEZAWA Hiroyuki
2009-06-11T05:33:15Z

On Tue, 9 Jun 2009 21:01:28 +0200
Johannes Weiner <hannes@cmpxchg.org> wrote:
> [resend with lists cc'd, sorry]
>
> +static int swap_readahead_ptes(struct mm_struct *mm,
> + unsigned long addr, pmd_t *pmd,
> + swp_entry_t *entries,
> + unsigned long cluster)
> +{
> + unsigned long window, min, max, limit;
> + spinlock_t *ptl;
> + pte_t *ptep;
> + int i, nr;
> +
> + window = cluster << PAGE_SHIFT;
> + min = addr & ~(window - 1);
> + max = min + cluster;

Johannes, I wonder there is no reason to use "alignment".
I think we just need to read "nearby" pages. Then, this function's
scan range should be

[addr - window/2, addr + window/2)
or some.

And here, too
> + if (!entries) /* XXX: shmem case */
> + return swapin_readahead_phys(entry, gfp_mask, vma, addr);
> + pmin = swp_offset(entry) & ~(cluster - 1);
> + pmax = pmin + cluster;

pmin = swp_offset(entry) - cluster/2.
pmax = swp_offset(entry) + cluster/2.

I'm sorry if I miss a reason for using "alignment".

Thanks,
-Kame