linux-kernel - Re: [RFC v2] mm: add page preemption

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Message-ID: <20191028122609.k5suvp7b57oxglvj@box>
Date:   Mon, 28 Oct 2019 15:26:09 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Hillf Danton <hdanton@...a.com>
Cc:     linux-mm <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Michal Hocko <mhocko@...e.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Minchan Kim <minchan@...nel.org>, Mel Gorman <mgorman@...e.de>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Jan Kara <jack@...e.cz>
Subject: Re: [RFC v2] mm: add page preemption

On Sat, Oct 26, 2019 at 07:28:08PM +0800, Hillf Danton wrote:
> @@ -218,6 +219,9 @@ struct page {
>  
>  #ifdef LAST_CPUPID_NOT_IN_PAGE_FLAGS
>  	int _last_cpupid;
> +#else
> +	int prio;
> +#define CONFIG_PAGE_PREEMPTION PP
>  #endif
>  } _struct_page_alignment;
>  

No.

There's a really good reason we trying hard to push the _last_cpuid into
page flags instead of growing the struct page by 4 bytes.

I don't think your feature worth 0.1% of RAM and a lot of cache misses
that this change would generate.

-- 
 Kirill A. Shutemov