linux-kernel - Re: [PATCH 2/2 - v2] MM: Discard NR_UNSTABLE_NFS, use NR

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Date:   Mon, 06 Apr 2020 10:14:16 +1000
From:   NeilBrown <neilb@...e.de>
To:     Michal Hocko <mhocko@...nel.org>, Jan Kara <jack@...e.cz>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Trond Myklebust <trondmy@...merspace.com>,
        "Anna.Schumaker\@Netapp.com" <Anna.Schumaker@...app.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-nfs@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2 - v2] MM: Discard NR_UNSTABLE_NFS, use NR_WRITEBACK instead.

On Fri, Apr 03 2020, Michal Hocko wrote:

> 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.

At the very end?
Do you mean not have "nr_unstable 0" appear at all, but having "dummy 0"
appear at the end just so that the number of lines doesn't decrease?
Am I misunderstanding?

Thanks,
NeilBrown

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