linux-kernel - Re: [PATCH v4 1/4] mm: memcontrol: use helpers to access page's memcg data

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Message-ID: <20201001182739.GA2706729@carbon.DHCP.thefacebook.com>
Date:   Thu, 1 Oct 2020 11:27:39 -0700
From:   Roman Gushchin <guro@...com>
To:     Johannes Weiner <hannes@...xchg.org>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Michal Hocko <mhocko@...nel.org>,
        <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
        <kernel-team@...com>
Subject: Re: [PATCH v4 1/4] mm: memcontrol: use helpers to access page's
 memcg data

On Thu, Oct 01, 2020 at 09:46:38AM -0400, Johannes Weiner wrote:
> On Wed, Sep 30, 2020 at 05:27:07PM -0700, Roman Gushchin wrote:
> > +/*
> > + * set_page_memcg - associate a page with a memory cgroup
> > + * @page: a pointer to the page struct
> > + * @memcg: a pointer to the memory cgroup
> > + *
> > + * Associates a page with a memory cgroup.
> > + */
> > +static inline void set_page_memcg(struct page *page, struct mem_cgroup *memcg)
> > +{
> > +	VM_BUG_ON_PAGE(PageSlab(page), page);
> > +
> > +	/*
> > +	 * Please, refer to page_memcg()'s description for the page and memcg
> > +	 * binding stability requirements.
> > +	 */
> > +	page->memcg_data = (unsigned long)memcg;
> > +}
> 
> Please delete and inline this as per previous feedback, thanks.

Why it's better?
It's ok for set_page_memcg(), but obviously worse for set_page_objcgs():
it was nice to have all bit magic in one place, in few helper functions.
And now it spills into several places. What's the win?

Thanks.