linux-kernel - Re: [PATCH 4/4] vfs: keep inodes with page cache off the inode shrinker LRU

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Message-ID: <YMzTSteDJkZkVziO@cmpxchg.org>
Date:   Fri, 18 Jun 2021 13:09:30 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Dave Chinner <david@...morbit.com>, Roman Gushchin <guro@...com>,
        Tejun Heo <tj@...nel.org>, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-team@...com
Subject: Re: [PATCH 4/4] vfs: keep inodes with page cache off the inode
 shrinker LRU

On Wed, Jun 16, 2021 at 06:30:43PM -0700, Andrew Morton wrote:
> On Wed, 16 Jun 2021 00:54:15 -0400 Johannes Weiner <hannes@...xchg.org> wrote:
> > On Wed, Jun 16, 2021 at 11:20:08AM +1000, Dave Chinner wrote:
> > > On Tue, Jun 15, 2021 at 02:50:09PM -0400, Johannes Weiner wrote:
> > > > On Tue, Jun 15, 2021 at 04:26:40PM +1000, Dave Chinner wrote:
> > > > > On Mon, Jun 14, 2021 at 05:19:04PM -0400, Johannes Weiner wrote:
> > > > > > @@ -1123,6 +1125,9 @@ static int __remove_mapping(struct address_space *mapping, struct page *page,
> > > > > >  			shadow = workingset_eviction(page, target_memcg);
> > > > > >  		__delete_from_page_cache(page, shadow);
> > > > > >  		xa_unlock_irq(&mapping->i_pages);
> > > > > > +		if (mapping_shrinkable(mapping))
> > > > > > +			inode_add_lru(mapping->host);
> > > > > > +		spin_unlock(&mapping->host->i_lock);
> > > > > >  
> > > > > 
> > > > > No. Inode locks have absolutely no place serialising core vmscan
> > > > > algorithms.
> > > > 
> > > > What if, and hear me out on this one, core vmscan algorithms change
> > > > the state of the inode?
> > > 
> > > Then the core vmscan algorithm has a layering violation.
> > 
> > You're just playing a word game here.
> 
> Don't think so.  David is quite correct in saying that vmscan shouldn't
> mess with inode state unless it's via address_space_operations?

It seemed to me the complaint was more about vmscan propagating this
state into the inode in general - effecting fs inode acquisitions and
LRU manipulations from the page reclaim callstack - regardless of
whether they are open-coded or indirect through API functions?

Since I mentioned better encapsulation but received no response...