Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Wed, 12 Feb 2020 10:26:45 -0800
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Johannes Weiner <hannes@cmpxchg.org>
Cc:     Rik van Riel <riel@surriel.com>, linux-fsdevel@vger.kernel.org,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Dave Chinner <david@fromorbit.com>,
        Yafang Shao <laoar.shao@gmail.com>,
        Michal Hocko <mhocko@suse.com>, Roman Gushchin <guro@fb.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Al Viro <viro@zeniv.linux.org.uk>, kernel-team@fb.com
Subject: Re: [PATCH] vfs: keep inodes with page cache off the inode shrinker
 LRU
Message-Id: <20200212102645.7b2e5b228048b6d22331e47d@linux-foundation.org>
In-Reply-To: <20200212163540.GA180867@cmpxchg.org>
References: <20200211175507.178100-1-hannes@cmpxchg.org>
        <29b6e848ff4ad69b55201751c9880921266ec7f4.camel@surriel.com>
        <20200211193101.GA178975@cmpxchg.org>
        <20200211154438.14ef129db412574c5576facf@linux-foundation.org>
        <20200212163540.GA180867@cmpxchg.org>
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Wed, 12 Feb 2020 11:35:40 -0500 Johannes Weiner <hannes@cmpxchg.org> wrote:

> Since the cache purging code was written for highmem scenarios, how
> about making it specific to CONFIG_HIGHMEM at least?

Why do I have memories of suggesting this a couple of weeks ago ;)

> That way we improve the situation for the more common setups, without
> regressing highmem configurations. And if somebody wanted to improve
> the CONFIG_HIGHMEM behavior as well, they could still do so.
> 
> Somethig like the below delta on top of my patch?

Does it need to be that complicated?  What's wrong with

--- a/fs/inode.c~a
+++ a/fs/inode.c
@@ -761,6 +761,10 @@ static enum lru_status inode_lru_isolate
 		return LRU_ROTATE;
 	}
 
+#ifdef CONFIG_HIGHMEM
+	/*
+	 * lengthy blah
+	 */
 	if (inode_has_buffers(inode) || inode->i_data.nrpages) {
 		__iget(inode);
 		spin_unlock(&inode->i_lock);
@@ -779,6 +783,7 @@ static enum lru_status inode_lru_isolate
 		spin_lock(lru_lock);
 		return LRU_RETRY;
 	}
+#endif
 
 	WARN_ON(inode->i_state & I_NEW);
 	inode->i_state |= I_FREEING;
_

Whatever we do will need plenty of testing.  It wouldn't surprise me
if there are people who unknowingly benefit from this code on
64-bit machines.