Re: [PATCH -V13 2/3] NUMA balancing: optimize page placement for memory tiering system

[Oscar Salvador]

On Tue, Mar 01, 2022 at 09:16:18AM +0800, Huang, Ying wrote:
> Hi, Oscar,

Hi Huang Ying

>  b. Make kswapd of the fast memory node to reclaim pages until the free
>     pages are a little more than the high watermark (named as promo
>     watermark).  If we want to promote some hot pages from the slow
>     memory to the fast memory, but the free pages of the fast memory
>     node will become lower than the high watermark after promotion, we
>     will wake up kswapd of the fast memory node to demote more cold
>     pages in the fast memory node to the slow memory node firstly.  This
>     will free some extra space in the fast memory node, so the hot pages
>     in the slow memory node can be promoted to the fast memory node.

What about this? Somehow it sounds clear to me.

"b. Define a new watermark called wmark_promo which is higher than wmark_high,
    and have kswapd reclaiming pages until free pages reach such watermark.
    The scenario is as follows: when we want to promote hot-pages from a slow
    memory to a fast memory, but fast memory's free pages would go lower than
    high watermark with such promotion, we wake up kswapd with wmark_promo
    watermark in order to demote cold pages and free us up some space.
    So, next time we want to promote hot-pages we might have a chance of
    doing so."

But I am fine with your updated write up as well, so if you spin a new
version:

Reviewed-by: Oscar Salvador <osalvador@xxxxxxx>


-- 
Oscar Salvador
SUSE Labs