linux-kernel - Re: [PATCH] block/psi: make PSI annotations of submit

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Date:   Wed, 30 Mar 2022 11:45:56 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     CGEL <cgel.zte@...il.com>, axboe@...nel.dk,
        viro@...iv.linux.org.uk, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        akpm@...ux-foundation.org, Yang Yang <yang.yang29@....com.cn>,
        Ran Xiaokai <ran.xiaokai@....com.cn>
Subject: Re: [PATCH] block/psi: make PSI annotations of submit_bio only work
 for file pages

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.