Re: [PATCHv6 05/37] thp: try to free page's buffers before attempt split

Kirill A. Shutemov
2017-02-13T14:32:47Z

On Thu, Feb 09, 2017 at 12:14:16PM -0800, Matthew Wilcox wrote:
> On Thu, Jan 26, 2017 at 02:57:47PM +0300, Kirill A. Shutemov wrote:
> > @@ -2146,6 +2146,23 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
> > goto out;
> > }
> >
> > + /* Try to free buffers before attempt split */
> > + if (!PageSwapBacked(head) && PagePrivate(page)) {
> > + /*
> > + * We cannot trigger writeback from here due possible
> > + * recursion if triggered from vmscan, only wait.
> > + *
> > + * Caller can trigger writeback it on its own, if safe.
> > + */
>
> It took me a few reads to get this. May I suggest:
>
> /*
> * Cannot split a page with buffers. If the caller has
> * already started writeback, we can wait for it to finish,
> * but we cannot start writeback if we were called from vmscan
> */

Yeah, that's better.

> > + if (!PageSwapBacked(head) && PagePrivate(page)) {
>
> Also, it looks weird to test PageSwapBacked of *head* and PagePrivate
> of *page*. I think it's correct, but it still looks weird.

I'll change this.

> Reviewed-by: Matthew Wilcox <mawilcox@microsoft.com>

Thanks!

--
Kirill A. Shutemov