Re: [LSF/MM/BPF TOPIC] State Of The Page

From: David Rientjes <rientjes@google.com>
To: Matthew Wilcox <willy@infradead.org>,
	Pasha Tatashin <tatashin@google.com>
Cc: Gao Xiang <hsiangkao@linux.alibaba.com>,
	lsf-pc@lists.linux-foundation.org, linux-fsdevel@vger.kernel.org,
	linux-mm@kvack.org, linux-block@vger.kernel.org,
	linux-ide@vger.kernel.org, linux-scsi@vger.kernel.org,
	linux-nvme@lists.infradead.org, bpf@vger.kernel.org
Subject: Re: [LSF/MM/BPF TOPIC] State Of The Page
Date: Wed, 1 Mar 2023 19:17:13 -0800 (PST)	[thread overview]
Message-ID: <a94384e5-cad2-fbdb-9187-7b626557e93a@google.com> (raw)
In-Reply-To: <Y/UiY/08MuA/tBku@casper.infradead.org>

On Tue, 21 Feb 2023, Matthew Wilcox wrote:

> On Wed, Feb 22, 2023 at 02:08:28AM +0800, Gao Xiang wrote:
> > On 2023/1/27 00:40, Matthew Wilcox wrote:
> > > I'd like to do another session on how the struct page dismemberment
> > > is going and what remains to be done.  Given how widely struct page is
> > > used, I think there will be interest from more than just MM, so I'd
> > > suggest a plenary session.
> > 
> > I'm interested in this topic too, also I'd like to get some idea of the
> > future of the page dismemberment timeline so that I can have time to keep
> > the pace with it since some embedded use cases like Android are
> > memory-sensitive all the time.
> 
> As you all know, I'm absolutely amazing at project management & planning
> and can tell you to the day when a feature will be ready ;-)
> 
> My goal for 2023 is to get to a point where we (a) have struct page
> reduced to:
> 
> struct page {
> 	unsigned long flags;
> 	struct list_head lru;
> 	struct address_space *mapping;
> 	pgoff_t index;
> 	unsigned long private;
> 	atomic_t _mapcount;
> 	atomic_t _refcount;
> 	unsigned long memcg_data;
> #ifdef LAST_CPUPID_NOT_IN_PAGE_FLAGS
> 	int _last_cpupid;
> #endif
> };
> 
> and (b) can build an allnoconfig kernel with:
> 
> struct page {
> 	unsigned long flags;
> 	unsigned long padding[5];
> 	atomic_t _mapcount;
> 	atomic_t _refcount;
> 	unsigned long padding2;
> #ifdef LAST_CPUPID_NOT_IN_PAGE_FLAGS
> 	int _last_cpupid;
> #endif
> };
> 

This is exciting to see and I'd definitely like to participate in the 
discussion.  Reducing struct page overhead is an important investment area 
for large hyperscalers from an efficiency standpoint, we strand a massive 
amount of memory due to struct page today.  I'd be particularly interested 
in a division-of-work discussion so that we can help to bridge any gaps 
that exist in realizing Matthew's vision, both short term and long term.