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

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Message-ID: <20180417112412.GB28901@castle.DHCP.thefacebook.com>
Date:   Tue, 17 Apr 2018 12:24:13 +0100
From:   Roman Gushchin <guro@...com>
To:     Michal Hocko <mhocko@...nel.org>
CC:     Johannes Weiner <hannes@...xchg.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Minchan Kim <minchan@...nel.org>, <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, Apr 16, 2018 at 01:41:44PM +0200, 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 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. 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.

IMO, this approach is much better than duplicating all kmalloc caches.
It's definitely has to be explored and discussed.

Thank you!