linux-ext4 - Re: [PATCH] fs/writeback: convert wbc_account_cgroup

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Message-ID: <ZvVrmBYTyNL3UDyR@casper.infradead.org>
Date: Thu, 26 Sep 2024 15:11:36 +0100
From: Matthew Wilcox <willy@...radead.org>
To: "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>
Cc: Theodore Ts'o <tytso@....edu>, Chao Yu <chao@...nel.org>,
	Jonathan Corbet <corbet@....net>,
	Josef Bacik <josef@...icpanda.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Koutný <mkoutny@...e.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	"Darrick J . Wong" <djwong@...nel.org>,
	Zefan Li <lizefan.x@...edance.com>, Tejun Heo <tj@...nel.org>,
	akpm@...ux-foundation.org, Christian Brauner <brauner@...nel.org>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	Jaegeuk Kim <jaegeuk@...nel.org>, Jan Kara <jack@...e.cz>,
	Chris Mason <clm@...com>, David Sterba <dsterba@...e.com>,
	cgroups@...r.kernel.org, linux-btrfs@...r.kernel.org,
	linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-f2fs-devel@...ts.sourceforge.net,
	linux-fsdevel@...r.kernel.org, mcgrof@...nel.org,
	gost.dev@...sung.com, linux-doc@...r.kernel.org,
	linux-xfs@...r.kernel.org, Pankaj Raghav <p.raghav@...sung.com>
Subject: Re: [PATCH] fs/writeback: convert wbc_account_cgroup_owner to take a
 folio

On Thu, Sep 26, 2024 at 04:01:21PM +0200, Pankaj Raghav (Samsung) wrote:
> Convert wbc_account_cgroup_owner() to take a folio instead of a page,
> and convert all callers to pass a folio directly except f2fs.
> 
> Convert the page to folio for all the callers from f2fs as they were the
> only callers calling wbc_account_cgroup_owner() with a page. As f2fs is
> already in the process of converting to folios, these call sites might
> also soon be calling wbc_account_cgroup_owner() with a folio directly in
> the future.

I was hoping for more from f2fs.  I still don't have an answer from them
whether they're going to support large folios.  There's all kinds of
crud already in these functions like:

        f2fs_set_bio_crypt_ctx(bio, fio->page->mapping->host,
                        page_folio(fio->page)->index, fio, GFP_NOIO);

and this patch is making it worse, not better.  A series of patches
which at least started to spread folios throughout f2fs would be better.
I think that struct f2fs_io_info should have its page converted to
a folio, for example.  Although maybe not; perhaps this structure can
carry data which doesn't belong to a folio that came from the page cache.
It's very hard to tell because f2fs is so mind-numbingly complex and
riddled with stupid abstraction layers.

But I don't know what the f2fs maintainers have planned.  And they won't
tell me despite many times of asking.