Re: [PATCH -mm -v10 1/3] mm, THP, swap: Delay splitting THP during swap out

[Minchan Kim]

On Thu, May 11, 2017 at 08:50:01AM +0800, Huang, Ying wrote:
< snip >

> >> > @@ -1125,8 +1125,28 @@ static unsigned long shrink_page_list(struct list_head *page_list,
> >> >  		    !PageSwapCache(page)) {
> >> >  			if (!(sc->gfp_mask & __GFP_IO))
> >> >  				goto keep_locked;
> >> > -			if (!add_to_swap(page, page_list))
> >> > +swap_retry:
> >> > +			/*
> >> > +			 * Retry after split if we fail to allocate
> >> > +			 * swap space of a THP.
> >> > +			 */
> >> > +			if (!add_to_swap(page)) {
> >> > +				if (!PageTransHuge(page) ||
> >> > +				    split_huge_page_to_list(page, page_list))
> >> > +					goto activate_locked;
> >> > +				goto swap_retry;
> >> > +			}
> >> 
> >> This is definitely better.
> >
> > Thanks.
> >
> >> 
> >> However, I think it'd be cleaner without the label here:
> >> 
> >> 			if (!add_to_swap(page)) {
> >> 				if (!PageTransHuge(page))
> >> 					goto activate_locked;
> >> 				/* Split THP and swap individual base pages */
> >> 				if (split_huge_page_to_list(page, page_list))
> >> 					goto activate_locked;
> >> 				if (!add_to_swap(page))
> >> 					goto activate_locked;
> >
> > Yes.
> >
> >> 			}
> >> 
> >> > +			/*
> >> > +			 * Got swap space successfully. But unfortunately,
> >> > +			 * we don't support a THP page writeout so split it.
> >> > +			 */
> >> > +			if (PageTransHuge(page) &&
> >> > +				  split_huge_page_to_list(page, page_list)) {
> >> > +				delete_from_swap_cache(page);
> >> >  				goto activate_locked;
> >> > +			}
> >> 
> >> Pulling this out of add_to_swap() is an improvement for sure. Add an
> >> XXX: before that "we don't support THP writes" comment for good
> >> measure :)
> >
> > Sure.
> >
> > It could be a separate patch which makes add_to_swap clean via
> > removing page_list argument but I hope Huang take/fold it when he
> > resend it because it would be more important with THP swap.
> 
> Sure.  I will take this patch as one patch of the THP swap series.
> Because the first patch of the THP swap series is a little big, I don't
> think it is a good idea to fold this patch into it.  Could you update
> the patch according to Johannes' comments and resend it?

Okay, I will resend this clean-up patch against on yours patch
after finishing this discussion.

Thanks.