Re: [PATCH 2/2 - v2] MM: Discard NR_UNSTABLE_NFS, use NR_WRITEBACK instead.

From: Michal Hocko <mhocko@kernel.org>
To: Jan Kara <jack@suse.cz>
Cc: NeilBrown <neilb@suse.de>, Christoph Hellwig <hch@infradead.org>,
	Trond Myklebust <trondmy@hammerspace.com>,
	"Anna.Schumaker@Netapp.com" <Anna.Schumaker@netapp.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	linux-mm@kvack.org, linux-nfs@vger.kernel.org,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/2 - v2] MM: Discard NR_UNSTABLE_NFS, use NR_WRITEBACK instead.
Date: Fri, 3 Apr 2020 13:03:58 +0200	[thread overview]
Message-ID: <20200403110358.GB22681@dhcp22.suse.cz> (raw)
In-Reply-To: <20200403094220.GA29920@quack2.suse.cz>

On Fri 03-04-20 11:42:20, Jan Kara wrote:
[...]
> > diff --git a/mm/vmstat.c b/mm/vmstat.c
> > index 78d53378db99..d1291537bbb9 100644
> > --- a/mm/vmstat.c
> > +++ b/mm/vmstat.c
> > @@ -1162,7 +1162,6 @@ const char * const vmstat_text[] = {
> >  	"nr_file_hugepages",
> >  	"nr_file_pmdmapped",
> >  	"nr_anon_transparent_hugepages",
> > -	"nr_unstable",
> >  	"nr_vmscan_write",
> >  	"nr_vmscan_immediate_reclaim",
> >  	"nr_dirtied",
> 
> This is probably the most tricky to deal with given how /proc/vmstat is
> formatted. OTOH for this file there's good chance we'd get away with just
> deleting nr_unstable line because there are entries added to it in the
> middle (e.g. in 60fbf0ab5da1 last September) and nobody complained yet.
> 
> What do mm people think? How were changes to vmstat counters handled in the
> past?

Adding new counters in the middle seems to be generally OK. I would be
more worried about removing counters though. So if we can simply print a
phone value at the very end then this should be a reasonable workaround.
-- 
Michal Hocko
SUSE Labs