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Date:   Thu, 1 Dec 2022 11:28:14 -0800 (PST)
From:   Hugh Dickins <hughd@google.com>
To:     Johannes Weiner <hannes@cmpxchg.org>
cc:     Hugh Dickins <hughd@google.com>,
        Shakeel Butt <shakeelb@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Michal Hocko <mhocko@suse.com>, linux-mm@kvack.org,
        cgroups@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm: remove lock_page_memcg() from rmap
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On Thu, 1 Dec 2022, Johannes Weiner wrote:
> On Wed, Nov 30, 2022 at 04:13:23PM -0800, Hugh Dickins wrote:
> 
> > And I don't know what will be best for the preliminary precharge pass:
> > doesn't really want the page lock at all, but it may be unnecessary
> > complication to avoid taking it then unlocking it in that pass.
> 
> We could make it conditional on target, which precharge doesn't pass,
> but I agree it's likely not worth optimizing that code at this point.

I hadn't noticed that NULL target so easily distinguishes that case:
unless it goes on to uglify things more (which I think it won't, seeing
now how there are already plenty of conditionals on target), I would
prefer to avoid the trylock and unlock in the precharge case; but
decide for yourself.

Hugh