linux-kernel - Re: [PATCH v4 6/8] mm/swap: implement workingset detection for anonymous LRU

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Message-ID: <20200402151413.GC2089@cmpxchg.org>
Date:   Thu, 2 Apr 2020 11:14:13 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     Joonsoo Kim <js1304@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Michal Hocko <mhocko@...nel.org>,
        Hugh Dickins <hughd@...gle.com>,
        Minchan Kim <minchan@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Mel Gorman <mgorman@...hsingularity.net>, kernel-team@....com,
        Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH v4 6/8] mm/swap: implement workingset detection for
 anonymous LRU

On Thu, Apr 02, 2020 at 02:50:28PM +0900, Joonsoo Kim wrote:
> 2020년 3월 24일 (화) 오후 3:25, Joonsoo Kim <js1304@...il.com>님이 작성:
> > The problem looks not that easy. Hmm...
> >
> > In current code, there is a large time gap between the shadow entries
> > are poped up and the page is charged to the memcg, especially,
> > for readahead-ed pages. We cannot maintain the shadow entries of
> > the readahead-ed pages until the pages are charged.
> >
> > My plan to solve this problem is propagating the charged mm to
> > __read_swap_cache_async(), like as file cache, charging when
> > the page is added on to the swap cache and calling workingset_refault()
> > there. Charging will only occur if:
> >
> > 1. faulted page
> > 2. readahead-ed page with the shadow entry for the same memcg
> >
> > Also, readahead only happens when shadow entry's memcg is the same
> > with the charged memcg. If not the same, it's mostly not ours so
> > readahead isn't needed.
> >
> > Please let me know how you think of the feasibility of this idea.
> 
> Hello, Johannes.
> 
> Could you let me know your opinion about the idea above?
> In fact, since your reply is delayed, I completed the solution about the
> above idea. If you want, I will submit it first. Then, we could discuss
> the solution more easily.

It's probably easiest if you send out your implementation and we
discuss it over the code.

Thanks!