linux-kernel - Re: [PATCH] mm: don't show nr_indirectly

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Message-ID: <20180427105549.GA8127@castle.DHCP.thefacebook.com>
Date:   Fri, 27 Apr 2018 11:55:54 +0100
From:   Roman Gushchin <guro@...com>
To:     Vlastimil Babka <vbabka@...e.cz>
CC:     David Rientjes <rientjes@...gle.com>,
        Michal Hocko <mhocko@...nel.org>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>, <linux-api@...r.kernel.org>,
        <kernel-team@...com>, Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH] mm: don't show nr_indirectly_reclaimable in /proc/vmstat

On Fri, Apr 27, 2018 at 11:17:01AM +0200, Vlastimil Babka wrote:
> On 04/26/2018 11:55 PM, David Rientjes wrote:
> > On Thu, 26 Apr 2018, Michal Hocko wrote:
> > 
> >>> Don't show nr_indirectly_reclaimable in /proc/vmstat,
> >>> because there is no need in exporting this vm counter
> >>> to the userspace, and some changes are expected
> >>> in reclaimable object accounting, which can alter
> >>> this counter.
> >>>
> >>> Signed-off-by: Roman Gushchin <guro@...com>
> >>> Cc: Vlastimil Babka <vbabka@...e.cz>
> >>> Cc: Matthew Wilcox <willy@...radead.org>
> >>> Cc: Andrew Morton <akpm@...ux-foundation.org>
> >>> Cc: Alexander Viro <viro@...iv.linux.org.uk>
> >>> Cc: Michal Hocko <mhocko@...e.com>
> >>> Cc: Johannes Weiner <hannes@...xchg.org>
> >>
> >> This is quite a hack. I would much rather revert the counter and fixed
> >> it the way Vlastimil has proposed. But if there is a strong opposition
> >> to the revert then this is probably the simples thing to do. Therefore
> >>
> > 
> > Implementing this counter as a vmstat doesn't make much sense based on how 
> > it's used.  Do you have a link to what Vlastimil proposed?  I haven't seen 
> > mention of alternative ideas.
> 
> It was in the original thread, see e.g.
> <08524819-14ef-81d0-fa90-d7af13c6b9d5@...e.cz>
> 
> However it will take some time to get that in mainline, and meanwhile
> the current implementation does prevent a DOS. So I doubt it can be
> fully reverted - as a compromise I just didn't want the counter to
> become ABI. TBH though, other people at LSF/MM didn't seem concerned
> that /proc/vmstat is an ABI that we can't change (i.e. counters have
> been presumably removed in the past already).
> 

Thank you, Vlastimil!
That pretty much matches my understanding of the case.

BTW, are you planning to work on supporting reclaimable objects
by slab allocators?

Thanks!