Re: [PATCH v4 8/8] mm/swap: count a new anonymous page as a reclaim_state's rotate

[Joonsoo Kim]

2020ë 3ì 24ì (í) ìì 2:43, Johannes Weiner <hannes@xxxxxxxxxxx>ëì ìì:
>
> On Mon, Mar 23, 2020 at 02:52:12PM +0900, js1304@xxxxxxxxx wrote:
> > From: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> >
> > reclaim_stat's rotate is used for controlling the ratio of scanning page
> > between file and anonymous LRU. All new anonymous pages are counted
> > for rotate before the patch, protecting anonymous pages on active LRU, and,
> > it makes that reclaim on anonymous LRU is less happened than file LRU.
> >
> > Now, situation is changed. all new anonymous pages are not added
> > to the active LRU so rotate would be far less than before. It will cause
> > that reclaim on anonymous LRU happens more and it would result in bad
> > effect on some system that is optimized for previous setting.
> >
> > Therefore, this patch counts a new anonymous page as a reclaim_state's
> > rotate. Although it is non-logical to add this count to
> > the reclaim_state's rotate in current algorithm, reducing the regression
> > would be more important.
> >
> > I found this regression on kernel-build test and it is roughly 2~5%
> > performance degradation. With this workaround, performance is completely
> > restored.
> >
> > v2: fix a bug that reuses the rotate value for previous page
>
> I agree with the rationale, but the magic bit in the page->lru list
> pointers seems pretty ugly.

Yes, pretty ugly.

> I wrote a patch a few years ago that split lru_add_pvecs into an add
> and a putback component. This was to avoid unintentional balancing
> effects of LRU isolations, but I think you can benefit from that
> cleanup here as well. Would you mind taking a look at it and maybe
> take it up into your series?
>
> https://lore.kernel.org/patchwork/patch/685708/

Thanks for pointing that.
I will remove the magic bit and imitate your patch to solve the problem
of this patch.

Thanks.