From: Johannes Weiner <hannes@cmpxchg.org>
To: Roman Gushchin <guro@fb.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Shakeel Butt <shakeelb@google.com>,
Michal Hocko <mhocko@kernel.org>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
kernel-team@fb.com
Subject: Re: [PATCH v4 1/4] mm: memcontrol: use helpers to access page's memcg data
Date: Thu, 1 Oct 2020 14:59:50 -0400 [thread overview]
Message-ID: <20201001185950.GB500308@cmpxchg.org> (raw)
In-Reply-To: <20201001182739.GA2706729@carbon.DHCP.thefacebook.com>
On Thu, Oct 01, 2020 at 11:27:39AM -0700, Roman Gushchin wrote:
> 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?
set_page_objcgs() is a worthwhile abstraction because it includes the
synchronization primitives that make it safe to use wrt
page_objcgs(). They encapsulate the cmpxchg and the READ_ONCE().
set_page_memcg() doesn't do any synchronization and relies fully on
the contextual locking. The name implies that it includes things to
make it safe wrt page_memcg(), which isn't true at all. It's a long
and misleading name for '='.
Btw, I really don't mind having this discussion, but please don't send
revisions that silently ignore feedback you don't agree with.
Thanks
next prev parent reply other threads:[~2020-10-01 19:01 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-01 0:27 [PATCH v4 0/4] mm: allow mapping accounted kernel pages to userspace Roman Gushchin
2020-10-01 0:27 ` [PATCH v4 1/4] mm: memcontrol: use helpers to access page's memcg data Roman Gushchin
2020-10-01 13:46 ` Johannes Weiner
2020-10-01 18:27 ` Roman Gushchin
2020-10-01 18:59 ` Johannes Weiner [this message]
2020-10-01 20:51 ` Roman Gushchin
2020-10-02 14:22 ` Johannes Weiner
2020-10-01 0:27 ` [PATCH v4 2/4] mm: memcontrol/slab: use helpers to access slab page's memcg_data Roman Gushchin
2020-10-01 0:27 ` [PATCH v4 3/4] mm: introduce page memcg flags Roman Gushchin
2020-10-01 13:44 ` Johannes Weiner
2020-10-01 0:27 ` [PATCH v4 4/4] mm: convert page kmemcg type to a page memcg flag Roman Gushchin
2020-10-01 13:48 ` Johannes Weiner
2020-10-01 17:00 ` Michal Koutný
2020-10-01 17:27 ` Johannes Weiner
2020-10-02 10:03 ` Michal Koutný
2020-10-02 13:25 ` Johannes Weiner
2020-10-01 18:30 ` Roman Gushchin
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