Re: [PATCH] lazy freeing of memory through MADV_FREE

[Rik van Riel <riel@redhat.com>]

Andrew Morton wrote:

> I've also merged Nick's "mm: madvise avoid exclusive mmap_sem".
> 
> - Nick's patch also will help this problem.  It could be that your patch
>   no longer offers a 2x speedup when combined with Nick's patch.
> 
>   It could well be that the combination of the two is even better, but it
>   would be nice to firm that up a bit.  

I'll test that.

>   I do go on about that.  But we're adding page flags at about one per
>   year, and when we run out we're screwed - we'll need to grow the
>   pageframe.

If you want, I can take a look at folding this into the
->mapping pointer.  I can guarantee you it won't be
pretty, though :)

> - I need to update your patch for Nick's patch.  Please confirm that
>   down_read(mmap_sem) is sufficient for MADV_FREE.

It is.  MADV_FREE needs no more protection than MADV_DONTNEED.

> Stylistic nit:
> 
>> +	if (PageLazyFree(page) && !migration) {
>> +		/* There is new data in the page.  Reinstate it. */
>> +		if (unlikely(pte_dirty(pteval))) {
>> +			set_pte_at(mm, address, pte, pteval);
>> +			ret = SWAP_FAIL;
>> +			goto out_unmap;
>> +		}
> 
> The comment should be inside the second `if' statement.  As it is, It
> looks like we reinstate the page if (PageLazyFree(page) && !migration).

Want me to move it?

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