linux-kernel - Re: [PATCH] mm/vmscan: restore zone_reclaim

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Message-Id: <20200630194755.61f56a55d46222f8d0c84bdd@linux-foundation.org>
Date:   Tue, 30 Jun 2020 19:47:55 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Baoquan He <bhe@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        ben.widawsky@...el.com, alex.shi@...ux.alibaba.com,
        dwagner@...e.de, tobin@...nel.org, cl@...ux.com, stable@...nel.org
Subject: Re: [PATCH] mm/vmscan: restore zone_reclaim_mode ABI

On Mon, 29 Jun 2020 16:37:37 -0700 Dave Hansen <dave.hansen@...el.com> wrote:

> On 6/29/20 4:30 PM, Baoquan He wrote:
> >> The only way I can plausibly think of "cleaning up" the RECLAIM_ZONE bit
> >> would be to raise our confidence that it is truly unused.  That takes
> >> time, and probably a warning if we see it being set.  If we don't run
> >> into anybody setting it or depending on it being set in a few years, we
> >> can remove it.
> > So adding the old bit back for compatibility looks good, thanks.
> > 
> > Then we have to be very careful when adding and reviewing new
> > interface introducing, should not leave one which might be used
> > in the future.
> > 
> > In fact, RECLAIM_ZONE is not completely useless. At least, when the old
> > bit 0 is set, it may enter into node_reclaim() in get_page_from_freelist(),
> > that makes it like a switch.
> > 
> > get_page_from_freelist {
> > 
> > 	...
> >                         if (node_reclaim_mode == 0 ||                                                                                             
> >                             !zone_allows_reclaim(ac->preferred_zoneref->zone, zone))
> >                                 continue;
> > 	...
> > }
> 
> Oh, that's a very good point.  There are a couple of those around.  Let
> me circle back and update the documentation and the variable name.  I'll
> send out another version.

Was the omission of cc:stable deliberate?