linux-kernel - Re: [PATCH 3/3] dcache: account external names as indirectly reclaimable memory

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Message-ID: <20180416122747.GM17484@dhcp22.suse.cz>
Date:   Mon, 16 Apr 2018 14:27:47 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Minchan Kim <minchan@...nel.org>, Roman Gushchin <guro@...com>,
        linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-team@...com
Subject: Re: [PATCH 3/3] dcache: account external names as indirectly
 reclaimable memory

On Mon 16-04-18 14:06:21, Vlastimil Babka wrote:
> On 04/16/2018 01:41 PM, Michal Hocko wrote:
> > On Fri 13-04-18 10:37:16, Johannes Weiner wrote:
> >> On Fri, Apr 13, 2018 at 04:28:21PM +0200, Michal Hocko wrote:
> >>> On Fri 13-04-18 16:20:00, Vlastimil Babka wrote:
> >>>> We would need kmalloc-reclaimable-X variants. It could be worth it,
> >>>> especially if we find more similar usages. I suspect they would be more
> >>>> useful than the existing dma-kmalloc-X :)
> >>>
> >>> I am still not sure why __GFP_RECLAIMABLE cannot be made work as
> >>> expected and account slab pages as SLAB_RECLAIMABLE
> >>
> >> Can you outline how this would work without separate caches?
> > 
> > I thought that the cache would only maintain two sets of slab pages
> > depending on the allocation reuquests. I am pretty sure there will be
> > other details to iron out and
> 
> For example the percpu (and other) array caches...
> 
> > maybe it will turn out that such a large
> > portion of the chache would need to duplicate the state that a
> > completely new cache would be more reasonable.
> 
> I'm afraid that's the case, yes.
> 
> > Is this worth exploring
> > at least? I mean something like this should help with the fragmentation
> > already AFAIU. Accounting would be just free on top.
> 
> Yep. It could be also CONFIG_urable so smaller systems don't need to
> deal with the memory overhead of this.
> 
> So do we put it on LSF/MM agenda?

If you volunteer to lead the discussion, then I do not have any
objections.

-- 
Michal Hocko
SUSE Labs