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Date:   Tue, 21 May 2019 14:01:44 +0900
From:   Minchan Kim <minchan@kernel.org>
To:     Matthew Wilcox <willy@infradead.org>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        LKML <linux-kernel@vger.kernel.org>,
        linux-mm <linux-mm@kvack.org>, Michal Hocko <mhocko@suse.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Tim Murray <timmurray@google.com>,
        Joel Fernandes <joel@joelfernandes.org>,
        Suren Baghdasaryan <surenb@google.com>,
        Daniel Colascione <dancol@google.com>,
        Shakeel Butt <shakeelb@google.com>,
        Sonny Rao <sonnyrao@google.com>,
        Brian Geffon <bgeffon@google.com>
Subject: Re: [RFC 0/7] introduce memory hinting API for external process
Message-ID: <20190521050144.GK10039@google.com>
References: <20190520035254.57579-1-minchan@kernel.org>
 <20190521014452.GA6738@bombadil.infradead.org>
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On Mon, May 20, 2019 at 06:44:52PM -0700, Matthew Wilcox wrote:
> On Mon, May 20, 2019 at 12:52:47PM +0900, Minchan Kim wrote:
> > IMHO we should spell it out that this patchset complements MADV_WONTNEED
> > and MADV_FREE by adding non-destructive ways to gain some free memory
> > space. MADV_COLD is similar to MADV_WONTNEED in a way that it hints the
> > kernel that memory region is not currently needed and should be reclaimed
> > immediately; MADV_COOL is similar to MADV_FREE in a way that it hints the
> > kernel that memory region is not currently needed and should be reclaimed
> > when memory pressure rises.
> 
> Do we tear down page tables for these ranges?  That seems like a good

True for MADV_COLD(reclaiming) but false for MADV_COOL(deactivating) at
this implementation.

> way of reclaiming potentially a substantial amount of memory.

Given that consider refauting are spread out over time and reclaim occurs
in burst, that does make sense to speed up the reclaiming. However, a
concern to me is anonymous pages since they need swap cache insertion,
which would be wasteful if they are not reclaimed, finally.