Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:18 as permitted sender) client-ip=2620:137:e000::1:18;
Date:   Wed, 30 Mar 2022 11:45:56 -0400
From:   Johannes Weiner <hannes@cmpxchg.org>
To:     Christoph Hellwig <hch@infradead.org>
Cc:     CGEL <cgel.zte@gmail.com>, axboe@kernel.dk,
        viro@zeniv.linux.org.uk, linux-block@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        akpm@linux-foundation.org, Yang Yang <yang.yang29@zte.com.cn>,
        Ran Xiaokai <ran.xiaokai@zte.com.cn>
Subject: Re: [PATCH] block/psi: make PSI annotations of submit_bio only work
 for file pages
Message-ID: <YkR7NPFIQ9h2AK9h@cmpxchg.org>
References: <20220316063927.2128383-1-yang.yang29@zte.com.cn>
 <YjiMsGoXoDU+FwsS@cmpxchg.org>
 <623938d1.1c69fb81.52716.030f@mx.google.com>
 <YjnO3p6vvAjeMCFC@cmpxchg.org>
 <20220323061058.GA2343452@cgel.zte@gmail.com>
 <62441603.1c69fb81.4b06b.5a29@mx.google.com>
 <YkRUfuT3jGcqSw1Q@cmpxchg.org>
 <YkRVSIG6QKfDK/ES@infradead.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <YkRVSIG6QKfDK/ES@infradead.org>
Precedence: bulk

On Wed, Mar 30, 2022 at 06:04:08AM -0700, Christoph Hellwig wrote:
> On Wed, Mar 30, 2022 at 09:00:46AM -0400, Johannes Weiner wrote:
> > If you want type distinction, we should move it all into MM code, like
> > Christoph is saying. Were swap code handles anon refaults and the page
> > cache code handles file refaults. This would be my preferred layering,
> > and my original patch did that: https://lkml.org/lkml/2019/7/22/1070.
> 
> FYI, I started redoing that version and I think with all the cleanups
> to filemap.c and the readahead code this can be done fairly nicely now:
> 
> http://git.infradead.org/users/hch/block.git/commitdiff/666abb29c6db870d3941acc5ac19e83fbc72cfd4

Yes, it's definitely much nicer now with the MM instantiating the
pages for ->readpage(s).

But AFAICS this breaks compressed btrfs (and erofs?) because those
still do additional add_to_page_cache_lru() and bio submissions.